The definition of nonalcoholic fatty liver disease (NAFLD) requires that (a) there is evidence of hepatic steatosis, either by imaging or by histology and (b) there are no causes for secondary hepatic fat accumulation such as significant alcohol consumption, use of steatogenic medication or hereditary disorders (Table 2). In the majority of patients, NAFLD is associated with metabolic risk factors such as obesity, diabetes mellitus, and dyslipidemia. NAFLD is histologically further categorized into nonalcoholic fatty liver (NAFL) and nonalcoholic steatohepatitis (NASH) (Table 3). NAFL is defined as the presence of hepatic steatosis with no evidence of hepatocellular injury in the form of ballooning of the hepatocytes. NASH is defined as the presence of hepatic steatosis and inflammation with hepatocyte injury (ballooning) with or without fibrosis.
Table 2. Common Causes of Secondary Hepatic Steatosis
|- Excessive alcohol consumption|
|- Hepatitis C (genotype 3)|
|- Wilson's disease|
|- Parenteral nutrition|
|- Medications (e.g., amiodarone, methotrexate, tamoxifen, corticosteroids)|
|- Reye's syndrome|
|- Medications (valproate, anti-retroviral medicines)|
|- Acute fatty liver of pregnancy|
|- HELLP syndrome|
|- Inborn errors of metabolism (e.g., LCAT deficiency, cholesterol ester storage disease, Wolman disease)|
Table 3. Nonalcoholic Fatty Liver Disease and related definitions
|Nonalcoholic Fatty Liver Disease (NAFLD)||Encompasses the entire spectrum of fatty liver disease in individuals without significant alcohol consumption, ranging from fatty liver to steatohepatitis and cirrhosis.|
|Nonalcoholic Fatty Liver (NAFL)||Presence of hepatic steatosis with no evidence of hepatocellular injury in the form of ballooning of the hepatocytes or no evidence of fibrosis. The risk of progression to cirrhosis and liver failure is minimal.|
|Nonalcoholic steatohepatitis (NASH)||Presence of hepatic steatosis and inflammation with hepatocyte injury (ballooning) with or without fibrosis. This can progress to cirrhosis, liver failure and rarely liver cancer.|
|NASH Cirrhosis||Presence of cirrhosis with current or previous histological evidence of steatosis or steatohepatitis|
|Cryptogenic Cirrhosis||Presence of cirrhosis with no obvious etiology. Patients with cryptogenic cirrhosis are heavily enriched with metabolic risk factors such as obesity and metabolic syndrome.|
|NAFLD Activity Score (NAS)||An unweighted composite of steatosis, inflammation, and ballooning scores. It is a useful tool to measure changes in liver histology in patients with NAFLD in clinical trials.|
Incidence and Prevalence in the General Population
The incidence of NAFLD has been investigated in a limited number of studies. Two Japanese studies9, 10 reported an incidence rate of 31 and 86 cases of suspected NAFLD per 1,000 person-years respectively, whereas another study from England showed a much lower incidence rate of 29 cases per 100,000 person-years.11 More studies are needed to better understand the incidence of NAFLD across different age, ethnic, and geographic groups.
The reported prevalence of NAFLD varies widely depending on the population studied and the definition used. The prevalence of histologically-defined NAFLD was 20% and 51% in two different studies comprised of potential living liver donors.12, 13 The reported prevalence of NAFLD when defined by liver ultrasound ranged between 17% and 46% depending on the population studied.4 In a study consisting of nearly 400 middle aged individuals, the prevalence of NAFLD defined by ultrasonography was 46% and the prevalence of histologically confirmed NASH was 12.2%.14 In the Dallas Heart Study, when assessed by MR spectroscopy the prevalence of NAFLD in the general population was 31%.15 The prevalence of suspected NAFLD when estimated using aminotransferases alone without imaging or histology ranged between 7% and 11%, but aminotransferases can be normal in individuals with NAFLD.4 In summary, estimates of the worldwide prevalence of NAFLD ranges from 6.3% to 33% with a median of 20% in the general population, based on a variety of assessment methods.4 On the other hand, the estimated prevalence of NASH is lower, ranging from 3 to 5%.4 The prevalence of NASH cirrhosis in the general population is not known.
Prevalence of NAFLD in High Risk Groups (Table 4)
Obesity is a common and well documented risk factor for NAFLD. Both excessive BMI and visceral obesity are recognized risk factors for NAFLD. In patients with severe obesity undergoing bariatric surgery, the prevalence of NAFLD can exceed 90% and up to 5% of patients may have unsuspected cirrhosis.4, 16-20 There is a very high prevalence of NAFLD in individuals with type 2 diabetes mellitus (T2DM).4 An ultrasonographic study of patients with T2DM showed a 69% prevalence of NAFLD.21 In another study, 127 of 204 diabetic patients displayed fatty infiltration on ultrasound, and 87% of the patients with fatty infiltration who consented to biopsy had histologic confirmation of NAFLD.22 High serum triglyceride levels and low serum HDL levels are very common in patients with NAFLD. The prevalence of NAFLD in individuals with dyslipidemia attending lipid clinics was estimated to be 50%.23
Table 4. Risk Factors Associated with NAFLD
|Obesity||Polycystic ovary syndrome|
|Type 2 diabetes mellitus||Hypothyroidism|
|Dyslipidemia||Obstructive Sleep apnea|
Age, gender and ethnicity are also associated with a differential prevalence for NAFLD.4 A number of studies have shown that the prevalence of NAFLD increases with age.24-28 The likelihood of disease progression to advanced fibrosis or mortality increases in older patients with NAFLD.29-31 Many recent studies have reported that male gender is a risk factor for fatty liver disease.4 For example, in a study of 26,527 subjects undergoing medical checkups, the prevalence of NAFLD was 31% in men and 16% in women.32 Compared to non-Hispanic whites, Hispanic individuals have significantly higher and non-Hispanic blacks have significantly lower prevalence of NAFLD.15, 33-35 The prevalence of NAFLD in American-Indian and Alaskan-Native populations appears lower, ranging from 0.6% to 2.2%, although the lack of histologic definition makes it likely that is an underestimate.36, 37
There are data to suggest that hypothyroidism, hypopituitarism, hypogonadism, sleep apnea, and polycystic ovary syndrome independent of obesity are important risk factors for the presence of NAFLD (Table 4).3
The evolution of hepatic histologic changes in patients with NAFL and NASH has been investigated by several studies, but these generally included smaller number of patients and had relatively modest duration of follow-up.4, 7 Nonetheless, it is generally agreed that patients with simple steatosis have very slow, if any, histological progression, while patients with NASH can exhibit histological progression to cirrhotic-stage disease.4, 7
The long term outcomes of patients with NAFLD and NASH have been reported in several studies.31, 38-45 Their detailed discussion is beyond the scope of this guideline, but their findings can be summarized as follows; (a) patients with NAFLD have increased overall mortality compared to matched control populations, (b) the most common cause of death in patients with NAFLD, NAFL and NASH is cardiovascular disease, and (c) patients with NASH (but not NAFL) have an increased liver-related mortality rate.
Another piece of indirect evidence that supports the progressive nature of NASH is in the features of cryptogenic cirrhosis which is closely related to NAFLD.46, 47 Patients with cryptogenic cirrhosis have disproportionately high prevalence of metabolic risk factors (T2DM, obesity, metabolic syndrome) typical of patients with NAFLD, their liver biopsies frequently show one or more features of NASH, and studies have demonstrated the loss of histological features of NASH with the development of cirrhosis.4, 7, 46, 47
Patients with NAFLD are at increased risk for HCC, but this risk is likely limited to those with advanced fibrosis and cirrhosis.48-53 Several studies investigated the natural history of NASH cirrhosis in comparison to patients with hepatitis C cirrhosis.54-57 One large prospective US-based study55 observed a lower rate of decompensation and mortality in patients with NASH cirrhosis as compared to patients with hepatitis C cirrhosis. However, a more recent international study56 of 247 NAFLD patients with advanced fibrosis and cirrhosis followed over a mean duration of 85.6 ± 54.5 months showed an overall 10-year survival of 81.5% that was not different from matched patients with hepatitis C cirrhosis. Importantly, both studies have shown that patients with NASH cirrhosis are at significantly lower risk for HCC than patients with hepatitis C cirrhosis.55, 56
Alcohol Consumption & Definition of NAFLD
By definition, NAFLD indicates the lack of any evidence of ongoing or recent consumption of significant quantities of alcohol. However, the precise definition of significant alcohol consumption in patients with suspected NAFLD is uncertain. A recent consensus meeting58 concluded that, for NASH clinical trials candidate eligibility purposes, significant alcohol consumption be defined as >21 drinks per week in men and >14 drinks per week in women over a 2-year period prior to baseline liver histology. Furthermore, this group recommended that validated questionnaires should be used to quantify the amount of alcohol consumption in the context of clinical trials. The definition of significant alcohol consumption in the published NAFLD literature has been inconsistent and ranged from > 1 alcoholic drink (∼ 10 grams of alcohol per one drink unit) per day to > 40 grams per day, and published studies have not always used gender-specific definitions.59 If self-reported alcohol consumption details are not consistent with clinical suspicion when evaluating a patient with suspected NAFLD, confirmation with a family member or a close friend should be considered.
1. Ongoing or recent alcohol consumption > 21 drinks on average per week in men and > 14 drinks on average per week in women is a reasonable definition for significant alcohol consumption when evaluating patients with suspected NAFLD in clinical practice. (Strength – 2, Quality - C)
Evaluation of Incidentally Discovered Hepatic Steatosis
Some patients undergoing thoracic and abdominal imaging for reasons other than liver symptoms, signs or biochemistry may demonstrate unsuspected hepatic steatosis. While this phenomenon is not uncommon in clinical practice, studies have not systematically examined the characteristics or natural history of NAFLD in this patient population.
2. When patients with unsuspected hepatic steatosis detected on imaging have symptoms or signs attributable to liver disease or have abnormal liver biochemistries, they should be evaluated as though they have suspected NAFLD and worked-up accordingly. (Strength – 1, Evidence -A)
3. In patients with unsuspected hepatic steatosis detected on imaging who lack any liver-related symptoms or signs and have normal liver biochemistries, it is reasonable to assess for metabolic risk factors (e.g., obesity, glucose intolerance, dyslipidemia) and alternate causes for hepatic steatosis such as significant alcohol consumption or medications. (Strength – 1, Evidence -A)
4. In patients with unsuspected hepatic steatosis detected on imaging who are asymptomatic and have normal liver biochemistries, a liver biopsy cannot be recommended. (Strength – 1, Evidence -B)
Screening in Primary Care, Diabetes, and Obesity Clinics
It can be argued that there should be systematic screening for NAFLD, at least among higher-risk individuals attending diabetes and obesity clinics. However, at present there are significant gaps in our knowledge regarding the diagnosis, natural history, and treatment of NAFLD. As liver biochemistries can be within normal ranges in patients with NAFLD and NASH, they may not be sufficiently sensitive to serve as screening tests, whereas liver ultrasound is potentially more sensitive but it is expensive and cumbersome as a screening test.
5. Screening for NAFLD in adults attending primary care clinics or high-risk groups attending diabetes or obesity clinics is not advised at this time due to uncertainties surrounding diagnostic tests and treatment options, along with lack of knowledge related to the long-term benefits and cost-effectiveness of screening. (Strength – 1, Evidence -B)
Screening of Family Members
Anecdotal experience and some published studies suggest familial clustering and heritability of NAFLD,60-63 but conclusive studies are lacking. In a retrospective cohort study, Willner et al. observed that 18% of patients with NASH have a similarly affected first degree relative.61 A small familial aggregation study observed that patients with NAFLD have a significantly higher number of first degree relatives with cirrhosis and a trend towards familial clustering of NAFLD or cryptogenic cirrhosis than matched healthy controls.62 In another familial aggregation study63 of overweight children with and without NAFLD, after adjusting for age, gender, race, and BMI, the heritability of MR-measured liver fat fraction was 0.386, and fatty liver was present in 18% of family members of children with NAFLD despite normal ALT and lack of obesity.
6. Systematic screening of family members for NAFLD is currently not recommended. (Strength – 1, Evidence - B)
The diagnosis of NAFLD requires that (a) there is hepatic steatosis by imaging or histology, (b) there is no significant alcohol consumption, (c) there are no competing etiologies for hepatic steatosis, and (d) there are no co-existing causes for chronic liver disease.
Common alternative causes of hepatic steatosis are significant alcohol consumption, hepatitis C, medications, parenteral nutrition, Wilson's disease, and severe malnutrition (Table 2). When evaluating a patient with newly suspected NAFLD, it is important to exclude co-existing etiologies for chronic liver disease including hemochromatosis, autoimmune liver disease, chronic viral hepatitis, and Wilson's disease.3 Mildly elevated serum ferritin is common in patients with NAFLD and it does not necessarily indicate increased iron stores.3, 64 Elevated serum ferritin and transferrin saturation in patients with suspected NAFLD should lead to testing for genetic hemochromatosis. Mutations in the HFE gene occur with variable frequency in patients with NAFLD and their clinical significance is unclear.64 One should consider a liver biopsy to assess hepatic iron concentration and to exclude significant hepatic injury and fibrosis in a patient with suspected NAFLD with elevated serum ferritin and a homozygote or compound heterozygote C282Y mutation in the HFE gene.65 Elevated serum autoantibodies are common in patients with NAFLD and are generally considered to be an epiphenomenon.3 In a recently published large study from the NASH Clinical Research Network, positive serum autoantibodies, defined as ANA > 1:160 or ASMA >1:40 were present in 21% of patients with well-phenotyped NAFLD and were not associated with more advanced histologic features.66
7. When evaluating a patient with suspected NAFLD, it is essential to exclude competing etiologies for steatosis and co-existing common chronic liver disease. (Strength – 1, Evidence - A)
8. Persistently high serum ferritin and increased iron saturation, especially in the context of homozygote or heterozygote C282Y HFE mutations may warrant a liver biopsy. (Strength – 1, Evidence - B)
9. High serum titers of autoantibodies in association with other features suggestive of autoimmune liver disease (very high aminotransferases, high globulin) should prompt a more complete work-up for autoimmune liver disease. (Strength – 1, Evidence - B)
Non-invasive assessment of steatohepatitis and advanced fibrosis in NAFLD
The natural history of NAFLD is fairly dichotomous – NAFL is generally benign whereas NASH can progress to cirrhosis, liver failure, and liver cancer. Existing dogma posits that liver biopsy is the most reliable approach for identifying the presence of steatohepatitis and fibrosis in patients with NAFLD, but it is generally acknowledged that biopsy is limited by cost, sampling error, and procedure-related morbidity and mortality. Serum aminotransferase levels and imaging tests such as ultrasound, CT, and MR do not reliably assess steatohepatitis and fibrosis in patients with NAFLD. Therefore, there has been significant interest in developing clinical prediction rules and non-invasive biomarkers for identifying steatohepatitis in patients with NAFLD,7 but their detailed discussion is beyond the scope of this practice guideline.
The presence of metabolic syndrome is a strong predictor for the presence of steatohepatitis in patients with NAFLD3, 7, 67-69 and may be used to best identify patients with persistently abnormal liver biochemistries who would benefit diagnostically and prognostically from a liver biopsy.
There has been intense interest in non-invasive methods to identify advanced fibrosis in patients with NAFLD7;these include the NAFLD Fibrosis Score70, Enhanced Liver Fibrosis (ELF) panel70 and transient elastography. The NAFLD Fibrosis Score is based on six readily available variables (age, BMI, hyperglycemia, platelet count, albumin, AST/ALT ratio) and it is calculated using the published formula (http://nafldscore.com). In a meta-analysis of 13 studies consisting of 3,064 patients,7 NAFLD Fibrosis Score has an AUROC of 0.85 for predicting advanced fibrosis (i.e., bridging fibrosis or cirrhosis) and a score < −1.455 had 90% sensitivity and 60% specificity to exclude advanced fibrosis whereas a score > 0.676 had 67% sensitivity and 97% specificity to identify the presence of advanced fibrosis. The ELF panel consists of plasma levels of three matrix turnover proteins (hyaluronic acid, TIMP-1, and PIIINP) had an AUROC of 0.90 with 80% sensitivity and 90% specificity for detecting advanced fibrosis.71
Circulating levels of cytokeratin-18 (CK18) fragments have been investigated extensively as novel biomarkers for the presence of steatohepatitis in patients with NAFLD.7, 72 Wieckowska et al., measured CK18 fragments in plasma that had been obtained from 44 consecutive patients with suspected NAFLD at the time of liver biopsy, and correlated the findings with hepatic immunohistochemistry data.70 Plasma CK18 fragments were markedly increased in patients with NASH compared with patients with simple steatosis or normal biopsies (median 765.7 U/L versus 202.4 U/L or 215.5 U/L, respectively; P < 0.001), and independently predicted NASH (OR 1.95; 95% CI 1.18-3.22 for every 50 U/L increase). This observation was reproduced in several subsequent studies and a recent meta-analysis estimated that plasma CK18 levels have a sensitivity of 78%, specificity of 87%, and an area under the receiver operating curve (AUROC) of 0.82 (95% CI: 0.78-0.88) for steatohepatitis in patients with NAFLD.7 Although these are very encouraging results, currently this assay is not commercially available. Furthermore, as each study utilized a study-specific cut-off value, there is not an established cut-off value for identifying steatohepatitis.
Transient elastography, which measures liver stiffness non-invasively, has been successful in identifying advanced fibrosis in patients with hepatitis B and hepatitis C. Although a recent meta-analysis showed high sensitivity and specificity for identifying fibrosis in NAFLD,7 it has a high failure rate in individuals with a higher BMI. Furthermore, it is not commercially available in the United States. Other imaging tools such as MR elastography, although commercially available in the United States, is rarely used in clinical practice.
A major limitation of these prediction models and biomarkers is that they have largely been investigated in cross-sectional studies and thus their utility in monitoring disease natural history, predicting outcomes or response to therapeutic intervention is unknown.
10. As the metabolic syndrome predicts the presence of steatohepatitis in patients with NAFLD, its presence can be used to target patients for a liver biopsy. (Strength – 1, Evidence - B)
11. NAFLD Fibrosis Score is a clinically useful tool for identifying NAFLD patients with higher likelihood of having bridging fibrosis and/or cirrhosis. (Strength – 1, Evidence - B)
12. Although serum/plasma CK18 is a promising biomarker for identifying steatohepatitis, it is premature to recommend in routine clinical practice. (Strength – 1, Evidence - B)
When to obtain a liver biopsy in patients with NAFLD?
Liver biopsy remains the gold standard for characterizing liver histology in patients with NAFLD. However, it is expensive and carries some morbidity and very rare mortality risk. Thus, it should be performed in those who would benefit the most from diagnostic, therapeutic guidance, and prognostic perspectives.
13. Liver biopsy should be considered in patients with NAFLD who are at increased risk to have steatohepatitis and advanced fibrosis. (Strength – 1, Evidence - B)
14. The presence of metabolic syndrome and the NAFLD Fibrosis Score may be used for identifying patients who are at risk for steatohepatitis and advanced fibrosis. (Strength – 1, Evidence - B)
15. Liver biopsy should be considered in patients with suspected NAFLD in whom competing etiologies for hepatic steatosis and co-existing chronic liver diseases cannot be excluded without a liver biopsy. (Strength – 1, Evidence - B)
MANAGEMENT OF PATIENTS WITH NAFLD
The management of patients with NAFLD consists of treating liver disease as well as the associated metabolic co-morbidities such as obesity, hyperlipidemia, insulin resistance and T2DM. As patients with NAFLD without steatohepatitis have excellent prognosis from a liver standpoint, treatments aimed at improving liver disease should be limited to those with NASH.
Many studies indicate that lifestyle modification may reduce aminotransferases and improve hepatic steatosis when measured either by ultrasound73-80 or MR imaging and spectroscopy.81-94 In a meta-analysis of 15 early case series and clinical studies spanning between 1967 through 2000, most studies reported reductions in aminotransferases and hepatic steatosis by ultrasound across a broad spectrum of diets of different caloric restriction intensities and macronutrient composition (low vs. high carbohydrate, low vs. high fat, saturated vs. unsaturated fat diets).95 However, these early studies were inconclusive as a result of being small, largely uncontrolled and few using histology as the primary endpoint. More recent uncontrolled studies also showed an improvement in aminotransferases and hepatic steatosis on histology with lifestyle modification.96-98
Orlistat (an enteric lipase inhibitor) in conjunction with lifestyle modification was investigated in two randomized controlled trials. In the study by Ziegler-Sagi et al.,99 orlistat reportedly improved ALT and steatosis by US, but its effect on liver histology could not be evaluated because the majority of patients did not undergo a follow-up liver biopsy. However, in the study by Harrison et al.,100 orlistat did not improve body weight or liver histology.
The best evidence for weight loss as a means to improve liver histology in NASH comes from a trial that randomized 31 obese persons with NASH to intensive lifestyle changes (diet, behaviour modification and 200 minutes a week of moderate physical activity for 48 weeks) versus structured basic education alone.101 The intensive arm had 9.3% weight loss (versus 0.2% in the dietary counseling alone arm) and led to an improvement in steatosis, necrosis and inflammation, but not fibrosis. Importantly, participants with ≥ 7% weight loss had significant improvement in steatosis, lobular inflammation, ballooning, and NAFLD Activity Score (NAS).101 There was a similar pattern in the study by Harrison et al.,100 where participants who lost > 5% body weight improved steatosis, whereas individuals with ≥ 9% weight loss had significant improvement in steatosis, lobular inflammation, ballooning, and NAS.
A number of recent studies used MR spectroscopy to assess changes in hepatic fat in response to lifestyle modification. The results from these studies using a variety of interventions, either by diet alone81, 83, 84, 89, 92, 93 or in combination with different exercise prescriptions,82, 85-88, 92, 94 have consistently reported a significant reduction in liver fat by an average of ∼40% (ranging from 20% to 81%). The degree of hepatic fat reduction was proportional to the intensity of the lifestyle intervention and generally required a body weight loss between ∼5 to 10%.82, 88, 92
The effect of exercise without dietary modification on hepatic steatosis was investigated in four studies using MR spectroscopy.102-105 Exercise programs consisted of 2-3 sessions a week of 30-60 minutes over a period of 6 to 12 weeks. In all but one study101 liver fat content diminished without a significant change in body weight.
16. Weight loss generally reduces hepatic steatosis, achieved either by hypocaloric diet alone or in conjunction with increased physical activity. (Strength – 1, Evidence - A)
17. Loss of at least 3-5% of body weight appears necessary to improve steatosis, but a greater weight loss (up to 10%) may be needed to improve necroinflammation. (Strength – 1, Evidence - B)
18. Exercise alone in adults with NAFLD may reduce hepatic steatosis but its ability to improve other aspects of liver histology remains unknown. (Strength – 1, Evidence - B)
INSULIN SENSITIZING AGENTS
Several studies investigated the effect of metformin on aminotransferases and liver histology in patients with NASH. Early small, open-label studies demonstrated a reduction in insulin resistance and aminotransferases106-108 but no significant improvement in liver histology.107, 108 An open-label trial consisting of 110 patients with NASH received either metformin 2 grams/day (55 patients), vitamin E 800 IU/day (28 patients) or dietary-induced weight loss (27 patients) for 12 months.109 Aminotransferases improved more with metformin than with vitamin E or diet alone. However, there was only a modest improvement in hepatic steatosis and inflammation in the subset of 17 patients undergoing paired liver biopsies with metformin treatment. In a 48-week open-label study in 26 patients, metformin improved NASH activity in only 30% of patients, although interpretation of the study was confounded by a significant weight loss in the responders (19% lost more than 10 kilograms).110 Haukeland et al.112 reported a similar lack of efficacy in a larger (n=48) randomized control trial (RCT) of metformin vs. placebo with a similar dietary and exercise intervention in both groups. Other studies also failed to show major benefit for metformin on hepatic insulin sensitivity, aminotransferases111-116 or liver histology.111, 113, 116 A recent meta-analysis4 concluded that 6-12 months of metformin plus lifestyle intervention did not improve aminotransferases or liver histology, compared with lifestyle intervention alone, independently of metformin dose or the presence of diabetes.
19. Metformin has no significant effect on liver histology and is not recommended as a specific treatment for liver disease in adults with NASH. (Strength – 1, Evidence - A)
Several studies investigated the effect of pioglitazone and rosiglitazone on aminotransferases and liver histology in adults with NASH. In an early uncontrolled open-label study117 in 22 subjects with biopsy-proven NASH, rosiglitazone improved aminotransferases and hepatic steatosis, ballooning and inflammation scores, but not fibrosis. But in a subsequent RCT, Ratziu et al.118 observed that rosiglitazone improved aminotransferases and hepatic steatosis, but not necroinflammation or fibrosis and its two-year open-label extension phase also showed similar results.119 Belfort et al.120 conducted a RCT of pioglitazone (45 mg/day) in patients with NASH who had impaired glucose tolerance or T2DM. Although there was a significant weight gain (2.5 ± 0.5 kg) with pioglitazone, it significantly improved aminotransferases, steatosis, ballooning, and inflammation. The NAS improved with pioglitazone in 73% compared to 24% of placebo-treated patients (P<0.001) and there was a trend towards improvement in fibrosis among patients randomized to pioglitazone (P=0.08). Aithal et al.121 performed a RCT of lifestyle intervention with either pioglitazone 30 mg/day or placebo for 12 months in a total of 74 patients with NASH. While steatosis did not improve significantly compared to placebo, hepatocellular injury and fibrosis improved significantly.1210 The PIVENS122 study is a large multicenter RCT that randomized 247 non-diabetic patients with NASH to pioglitazone (30 mg/day), vitamin E (800 IU/day), or placebo for 24 months. The primary endpoint was an improvement in NAS ≥ 2 points with at least 1 point improvement in hepatocellular ballooning and 1-point improvement in either the lobular inflammation or steatosis score, and no increase in the fibrosis score.122 It was achieved in 19% in the placebo group compared to 34% in the pioglitazone group (P=0.04 vs. placebo) and 43% in the vitamin E group (P=0.001 vs. placebo).122 Because this study consisted of two primary comparisons (pioglitazone vs. placebo and vitamin E vs. placebo), a P-value of 0.025 was considered to be significant a priori. Therefore, although there were histological benefits associated with pioglitazone, this study concluded that pioglitazone did not meet the primary end point. However, resolution of NASH, a key secondary end point, was achieved in significantly higher number of patients receiving pioglitazone than receiving placebo (47% vs. 21%, P=0.001).122 Of note, pioglitazone was associated with a 4.7 kg weight gain compared to placebo (P<0.001). Vitamin E and pioglitazone were well tolerated and there were no differences in other adverse events.
A recent meta-analysis4 that included 5 RCTs showed that pioglitazone significantly improved steatosis (OR 4.05, 95% CI 2.58-6.35) and inflammation (OR 3.53, 95% CI 2.21-5.64), but not fibrosis (OR 1.40, 95% CI 0.87-2.24).
There has been considerable debate about the long-term safety of TZDs regarding cardiovascular disease, congestive heart failure (CHF), bladder cancer, and bone loss. In a recent meta-analysis123 of 19 trials enrolling a total of 16,390 patients with T2DM, pioglitazone treatment was associated with a significant reduction (∼18%) in the primary outcome of death, myocardial infarction, or stroke (P=0.005). However, there was also a higher rate of CHF with pioglitazone (2.3% vs. 1.8% in the control group, P=0.002), so caution must be exercised when considering its use in patients with impaired myocardial function. Due to increased risk of coronary events, rosiglitazone is no longer marketed in Europe and its use is highly restricted in the United States.
20. Pioglitazone can be used to treat steatohepatitis in patients with biopsy-proven NASH. However, it should be noted that majority of the patients who participated in clinical trials that investigated pioglitazone for NASH were non-diabetic and that long term safety and efficacy of pioglitazone in patients with NASH is not established. (Strength – 1, Evidence - B)
Oxidative stress is considered to be a key mechanism of hepatocellular injury and disease progression in subjects with NASH. Vitamin E is an anti-oxidant and has been investigated to treat NASH.124-128 Comparison between these trials is difficult due to varying criteria for entry into the study, different doses of vitamin E and unclear formulations of vitamin E used which could affect its bioavailability, the additional use of other anti-oxidants or other drugs and limited histologic data to assess outcomes. Also, most studies were relatively under-powered and did not meet or publish CONSORT criteria for clinical trials. Despite these limitations, it can be summarized that (1) the use of vitamin E is associated with a decrease in aminotransferases in subjects with NASH, (2) studies where histologic endpoints were evaluated indicate that vitamin E causes improvement in steatosis, inflammation, and ballooning and resolution of steatohepatitis in adults with NASH, and (3) vitamin E has no effect on hepatic fibrosis. Although two meta-analyses8, 129 failed to observe significant histological benefits with vitamin E in patients with NASH, these analyses were conducted before PIVENS122 and TONIC130 trials were published. In the largest clinical trial (PIVENS)122 reported to date, the pure form of rrr α-tocopherol was orally administered at a dose of 800 IU/day for 96 weeks. The primary endpoint as stated previously was achieved in a significantly greater number of participants receiving vitamin E compared to placebo (42% vs. 19%, P< 0.001, number needed to treat= 4.4).
One concern with vitamin E is the controversial issue of whether it increases all-cause mortality. Some meta-analyses have reported an increase in all-cause mortality with high dose vitamin E,131, 132 but others failed to confirm such an association.133-135 A recently published RCT showed that vitamin E administered at a dose of 400 IU/day increased the risk of prostate cancer in relatively healthy men (absolute increase of 1.6 per 1000 person years of vitamin E use).136
21. Vitamin E (α-tocopherol) administered at daily dose of 800 IU/day improves liver histology in non-diabetic adults with biopsy-proven NASH and therefore it should be considered as a first-line pharmacotherapy for this patient population. (Strength -1, Quality - B)
22. Until further data supporting its effectiveness become available, vitamin E is not recommended to treat NASH in diabetic patients, NAFLD without liver biopsy, NASH cirrhosis, or cryptogenic cirrhosis (Strength - 1, Quality - C)
Ursodeoxycholic acid (UDCA), Omega-3 fatty acids, and Miscellaneous Agents
Several studies126, 137-140 investigated UDCA (conventional and high doses) to improve aminotransferases and steatosis in patients with NAFLD and liver histology in patients with NASH. All but one study139 have been proof-of-concept studies with small numbers of participants and/or surrogate endpoints. Notably, a single large multicenter RCT convincingly showed that UDCA offers no histological benefit over placebo in patients with NASH.139 Omega-3 fatty acids, currently approved in the United States to treat hypertriglyceridemia, have been investigated to treat NAFLD both in animal models and in humans.141 A recent review by Masterton et al.,142 of published literature related to omega-3 fatty acids in NAFLD, found experimental evidence to support their use but the interpretation of human studies was limited by small sample size and methodological flaws. A large multicenter study of one omega-3 fatty acid (eicosapentanoic acid) to treat NASH is ongoing in the United States.. More than a dozen other miscellaneous agents have been investigated in small, proof-of-concept studies and their detailed evaluation is beyond the scope of this guideline.
23. UDCA is not recommended for the treatment of NAFLD or NASH. (Strength – 1, Quality – B)
24. It is premature to recommend omega-3 fatty acids for the specific treatment of NAFLD or NASH but they may be considered as the first line agents to treat hypertriglyceridemia in patients with NAFLD. (Strength – 1, Quality – B)
As the majority of patients undergoing bariatric surgery have associated fatty liver disease, there has been an interest in foregut bariatric surgery as a potential treatment option for NASH. There are no RCTs that evaluated any type of foregut bariatric surgical procedure to specifically treat NAFLD or NASH. However, there are several retrospective and prospective cohort studies that compared liver histology in the severely obese individuals before and after bariatric surgery. Unfortunately, in the majority of these studies, post-bypass liver biopsies were performed at varying intervals and only in selected patients undergoing surgical procedures such as hernia repair or adhesiolysis. One exception is the study by Mathurin et al.,143 that prospectively correlated clinical and metabolic data with liver histology before and 1 and 5 years after bariatric surgery in 381 adult patients with severe obesity. Gastric band, bilio-intestinal bypass, and gastric bypass were done in 56%, 23%, and 21%, respectively. Compared to baseline, there was a significant improvement in the prevalence and severity of steatosis and ballooning at 1 and 5 years following bariatric surgery. In patients with probable or definite NASH at baseline (n=99), there was a significant improvement in steatosis, ballooning, and NAS and resolution of probable or definite NASH at 1 and 5 years following bariatric surgery. Most histological benefits were evident at 1 year with no differences in liver histology between 1 and 5 years following bariatric surgery. Intriguingly, a minor but statistically significant increase in mean fibrosis score was noted at 5 years after the bariatric surgery (from 0.27± 0.55 at baseline to 0.36 ± 0.59, P=0.001). Despite this increase, at 5 years 96% of patients exhibited fibrosis score ≤ F1 and 0.5% had F3, indicating there is no clinically significant worsening in fibrosis that can be attributed directly to the procedure. In the important subgroup of patients with probable or definite NASH at baseline, there was no worsening of fibrosis at 1 and 5 years, compared to baseline liver biopsy. As no patient in the study had F3 or F4 at baseline, the effect of bariatric surgery in those with advanced fibrosis and cirrhosis could not be evaluated.
Two meta-analyses144, 145 evaluated the effect of bariatric surgery on the liver histology in patients with NAFLD. The meta-analysis by Mummadi et al.,144 showed that steatosis, steatohepatitis, and fibrosis appear to improve or completely resolve after bariatric surgery. However, a recently published Cochrane review145 concluded that lack of randomized clinical trials or quasi-randomized clinical studies prevents definitive assessment of benefits and harms of bariatric surgery as a therapeutic approach for patients with NASH.
25. Foregut bariatric surgery is not contraindicated in otherwise eligible obese individuals with NAFLD or NASH (but without established cirrhosis). (Strength – 1, Quality – A)
26. The type, safety and efficacy of foregut bariatric surgery in otherwise eligible obese individuals with established cirrhosis due to NAFLD are not established. (Strength – 1, Quality – B)
27. It is premature to consider foregut bariatric surgery as an established option to specifically treat NASH (1B)
Alcohol use in patients with NAFLD and NASH
Heavy alcohol consumption is a risk factor for chronic liver disease and should be avoided by patients with NAFLD and NASH. The National Institute on Alcohol Abuse and Alcoholism (NIAAA) defines heavy or at-risk drinking as more than 4 drinks on any day or more than 14 drinks per week in men or more than 3 drinks on any day or 7 drinks per week in women.146 Several recent cross-sectional studies147-153 suggest a beneficial effect of light alcohol consumption (on average less than one drink per day) on the presence (defined either biochemically or by imaging) and severity of NAFLD. There are no studies reporting the effect of ongoing alcohol consumption on disease severity or natural history of NAFLD or NASH. The effects of light drinking on the cardiovascular system and cancer risks, if any, have not been investigated in individuals with NAFLD.
28. Patients with NAFLD should not consume heavy amounts of alcohol (Strength -1, Quality – B)
29. No recommendation can be made with regards to non-heavy consumption of alcohol by individuals with NAFLD. (Strength – 1, Quality – B)
Statin use in patients with NAFLD and NASH
Patients with NAFLD and NASH are at increased risk for cardiovascular disease and several studies have established cardiovascular disease as their most common cause of death.6 Patients with NAFLD should be risk stratified for cardiovascular disease, and their cardiovascular risk factors should be managed accordingly.154 The treatment of dyslipidemia should be considered in the overall frame work of cardiovascular risk reduction in patients with NAFLD.154
Statins are an important class of agents to treat dyslipidemia, and yet there is continued reluctance to use statins in patients with suspected or established chronic liver disease, including NAFLD and NASH. Although elevated aminotransferases are not uncommon in patients receiving statins, serious liver injury from statins is rarely seen in clinical practice. Over the last decade, one RCT and several retrospective and prospective studies155-159 have established that (a) statins are safe in patients with liver disease and (b) there is no evidence that patients with chronic liver disease including at NAFLD and NASH are at higher risk for serious liver injury from statins than those without liver disease.
Several studies have suggested that statins may improve liver biochemistries and histology in patients with NASH.159-167 These studies consisted of small numbers of patients and have not been rigorously designed. A recent post-hoc analysis of the cardiovascular outcomes study, GREACE,165 observed that statins significantly improve liver biochemistries and cardiovascular outcomes in patients with elevated liver enzymes likely due to NAFLD. There are no RCTs with histological endpoints which investigated statins to treat NASH.
30. Given the lack of evidence to show that patients with NAFLD and NASH are at increased risk for serious drug-induced liver injury from statins, statins can be used to treat dyslipidemia in patients with NAFLD and NASH. (Strength – 1, Quality – B)
31. Until RCTs with histological endpoints prove their efficacy, statins should not be used to specifically treat NASH. (Strength – 1, Quality – B)
NAFLD in patients with other chronic liver diseases
Because of the high prevalence of risk factors for NAFLD and NASH, it is not uncommon for patients with other chronic liver diseases to exhibit co-existing histological features of NAFLD.168 Coexistent hepatic steatosis is common in chronic hepatitis C (HCV) infection and is strongly associated with more advanced liver disease.169-171 Another large study showed high prevalence of steatosis (40.5%) and steatohepatitis (15%) in patients with primary biliary cirrhosis (PBC),172 although at least some of the steatosis and steatohepatitis in that study was suspected to be due to alcohol consumption. In clinical practice, it is not uncommon for obese and/or diabetic patients with autoimmune liver disease to exhibit steatosis and steatohepatitis in their liver biopsies.
Previous studies have shown that obesity, insulin resistance, and hepatic steatosis are associated with a lower response to pegylated interferon and ribavirin for the treatment of HCV.173-175 Obesity does not have a similar negative impact on the response to newer protease-inhibitor based anti-viral regimens,176-180 but the impact of insulin resistance and hepatic steatosis has not yet been investigated sufficiently. It is not known if the treatment of steatosis and steatohepatitis alters the natural history of other chronic liver diseases such as HCV and PBC. Furthermore, it is not known if agents such as vitamin E and pioglitazone are effective to treat steatosis and steatohepatitis when present in patients with other chronic liver diseases.
32. When steatosis and steatohepatitis are evident in patients with other types of chronic liver disease, it is important to assess for metabolic risk factors and alternate etiologies for hepatic steatosis. (Strength – 1, Quality – B)
33. In patients with other types of chronic liver diseases who have co-existing NAFLD and NASH, there are no data to support the use of vitamin E or pioglitazone to improve the liver disease. (Strength – 1, Quality – B)
Miscellaneous Recommendations Pertinent to Clinical Practice
34. Patients with NASH cirrhosis should be screened for gastroesophageal varices according to the AASLD/ACG practice guidelines.181(Strength – 1, Quality – B)
35. Patients with NASH cirrhosis should be considered for HCC screening according to the AASLD/ACG practice guidelines.182(Strength – 1, Quality – B)
36. Current evidence does not support routinely repeating a liver biopsy in patients with NAFL or NASH. (Strength – 2, Quality – C)
Aspects of NAFLD Specific to Children and Adolescents
Recognition of NAFLD in children is essential to understanding the origin of disease in those likely to be most genetically or environmentally susceptible. Adults with onset of NAFLD in childhood may be most at risk for early or severe complications. Definition of NAFLD in childhood is the same as in adults. Children are reported with NAFLD as early as 2 years and with NASH-related cirrhosis as early as age 8.183, 184
Prevalence and Risk Factors
Estimation of population prevalence in children presents difficulties for the same reasons detailed above in adults. Estimates vary based upon the type of test or imaging, the cut-points for detection, and the age, sex, race and ethnicity of the geographic region sampled. A school-based study of obese children in Minnesota, California, Texas and Louisiana, using abnormal serum ALT as a surrogate marker (>40U/L), found that 23% of 17-18 year olds had elevated unexplained ALT.183 An autopsy study using the “gold standard” of liver histology examined 742 children between the ages of 2-19 y who died from unnatural causes. The estimated NAFLD prevalence was 9.6% when adjusted for age, gender, race and ethnicity.184 Multivariate analyses showed that obesity, older age (in adolescence), male gender, and Hispanic ethnicity are independent predictors of fatty liver prevalence.
Natural History of NAFLD in Children
A single retrospective single center report has been published on the natural history of NAFLD in 66 children.185 Only 5 had serial biopsies, obtained for unspecified reasons over varying intervals, averaging 41 months between biopsies. Of these 5 children, 4 had progression of fibrosis. Four of the 5 underwent liver transplantation and 2 died of cirrhosis. Clearly, more robust prospective data are needed on larger number of children to better understand the natural history of NAFLD in children.
Screening for NAFLD in Children
NAFLD is under-diagnosed in children due to lack of recognition, screening or appreciation of associated complications by health care providers. One study showed that less than a third of obese children were screened for NAFLD at clinic visits.186 Children may not be recognized as obese at visits and age-appropriate norms for body mass index may go unacknowledged. Abdominal adiposity may mask detection of hepatomegaly by palpation during physician examination. As in adults, children with features of metabolic syndrome such as obesity, hypertension, insulin resistance and dyslipidemia63 are at higher risk for NAFLD and particular histopathological features of NAFLD correlate with components of metabolic syndrome.187 Thus, identification of children at risk for NAFLD could occur in general health provider settings as well as in specialty clinics for nutrition, gastroenterology, hepatology, endocrinology and bariatric surgery. Children may also exhibit NAFLD incidentally discovered while undergoing imaging, but there are no studies evaluating how to proceed with children identified in this fashion. Recently, the summary report of an expert committee suggested biannual screening for liver disease with serum ALT and AST starting at age 10 years in obese children and those with BMI of 85th to 94th percentile with other risk factors.188
Penetrance of NAFLD has been demonstrated in family members of children with NAFLD.63 The likelihood of first, second and third degree relatives exhibiting abnormally high fat fractions (by MRI estimation) relative to body mass index is much more highly correlated in those related to a child with NAFLD than to those who are related to an age, gender and BMI-matched child without NAFLD.
Diagnosis in children
Given the relatively early onset, caregivers must give additional consideration to the possibility of monogenic disorders that present as fatty liver disease in very young children. Considerations include inborn errors of fatty acid or carnitine metabolism, peroxisomal disorders, lysosomal storage disorders, Wilson's disease, and cystic fibrosis.189 However, as in adults, positive serum autoantibodies are present in a significant population of children with biopsy-proven NAFLD and on some occasion liver biopsy is required to discriminate between autoimmune hepatitis and NAFLD.63 Obviously, the confounding factor of alcoholism is much less common in children and standard questionnaires for quantifying alcohol intake are usually unnecessary.
37. Children with fatty liver who are very young or not overweight should be tested for monogenic causes of chronic liver disease such as fatty acid oxidation defects, lysosomal storage diseases and peroxisomal disorders, in addition to those causes considered for adults. (Strength – 2, Quality – C)
38. Low serum titers of autoantibodies are often present in children with NAFLD, but higher titers, particularly in association with higher serum aminotransferases and high globulin should prompt a liver biopsy to evaluate for possible autoimmune hepatitis. (Strength – 2, Quality – B)
39. Due to a paucity of evidence, a formal recommendation cannot be made with regards to screening for NAFLD in overweight and obese children despite a recent expert committee recommendation for biannual screening for liver disease with liver enzyme measurements in this population. (Strength –1, Quality – B).
When to obtain a liver biopsy for suspected pediatric NAFLD?
The decision to perform a liver biopsy in a child to confirm the diagnosis of NAFLD must be weighed against the risks associated with biopsy and the likelihood that the result will impact management. In children with an uncertain diagnosis, biopsy may rule out potential drug hepatotoxicity or lack of clarity due to presence of serum autoantibodies. When there is an interest in grading or staging NAFLD, instead of submitting all children with NAFLD to a liver biopsy it would be optimal to identify those children who are more likely to have NASH. The paucity of natural history data confounds the decision to biopsy since alteration of long-term outcomes with treatment based on severity of histology at baseline is unknown.
As in adults, development of noninvasive biomarkers or imaging to identify those at risk for more rapid progression or severe disease onset is desirable. Particularly, accurate markers of cellular injury and fibrosis are needed. Two studies suggested that ELF score can be used to accurately predict fibrosis in children with NAFLD, but both studies consisted of relatively small numbers of children and fewer with advanced fibrosis.190, 191 There is reported benefit in predicting fibrosis stage in pediatric patients, with a AUROC of 0.92, although only 9 of the 76 subjects studied had fibrosis stage 3 or more.190 Validation of the serum CK18 levels to evaluate NASH needs to be undertaken in children with NAFLD.
40. Liver biopsy in children with suspected NAFLD should be performed in those where the diagnosis is unclear, where there is possibility of multiple diagnoses, or before starting therapy with potentially hepatotoxic medications. (Strength – 1, Quality – B)
41. A liver biopsy to establish a diagnosis of NASH should be obtained prior to starting children on pharmacologic therapy for NASH. (Strength – 2, Quality – C)
NAFLD Histology in Children
Histopathology of children with NAFLD can differ from that found in adults.192 As in adults, children can present with pronounced features of hepatocellular injury, lobular inflammation, and peri-sinusoidal fibrosis, but there is a unique pattern of unclear significance also recognized in children. This pattern is typified by marked macrovesicular hepatocellular steatosis, portal inflammation and portal fibrosis in the absence of ballooning.192, 194
42. Pathologists interpreting pediatric NAFLD biopsies should recognize the unique pattern frequently found in children to not misidentify pediatric NAFLD. (Strength – 1, Quality – B)
Treatment in Children
Recommendations for pediatric treatment options are limited by a small number of randomized clinical trials and insufficient information on natural history to assess risk-benefit. The overall goal is to improve a child's quality of life and reduce longer term cardiovascular and liver morbidity and mortality. Given that early-onset likely indicates higher likelihood of later complications, attempts should be made to identify children who will benefit from intervention.
Since most pediatric NAFLD patients are obese, addressing their obesity is the first step. An open label study195 in 84 Italian children with biopsy-proven NAFLD showed that >20% body weight reduction over 12 months resulted in improvement in serum ALT and steatosis by ultrasonography in most children with NAFLD. Reportedly, 94% of the 70 enrolled subjects were able to achieve this weight loss goal using caloric restriction and exercise advice. Since liver biopsies were not performed at the end of the study, the effect of lifestyle intervention on liver histology could not be determined. In another study, Nobili et al.196 randomized 53 children with biopsy-proven NAFLD to lifestyle modification plus antioxidant therapy or lifestyle modification and placebo. Antioxidant therapy did not improve liver histology, but children in both groups showed significant improvement in steatosis, inflammation, ballooning, and the NAS. Although there are no randomized controlled trials of intensive lifestyle modification compared to standard-of-care advice, these two studies indicate that lifestyle modification is beneficial in children with NAFLD.
No information exists on recommending any particular type of diet or exercise. Further studies are needed to assess the efficacy of specific diets. Recommendations for overweight pediatric NAFLD patients should include consultation with a registered dietitian to assess quality of diet and measurement of caloric intake, adoption of American Heart Association dietary strategies, and regular aerobic exercise progressing in difficulty as fitness allows.197, 198 Enlisting other willing family members to adopt diet and exercise goals may aid compliance.
As in adults, clinical trials for pediatric NAFLD generally targeted insulin resistance or oxidative stress. Open-label proof-of-concept studies have utilized changes in serum ALT or liver brightness on ultrasound as endpoints.189 Agents evaluated thus far include metformin, vitamin E, ursodeoxycholic acid and delayed-release cysteamine.189 Recently, a large multicenter RCT using change in histology as a secondary endpoint was published.130 This study, called TONIC, compared the efficacy of vitamin E or metformin to placebo in 8-17 year olds with NAFLD.130 Although the primary outcome of sustained reduction of ALT was not different among the 3 groups, there were statistically significant improvements in NAS and resolution of NASH (P<0.006) with vitamin E treatment compared to placebo over 96 weeks.130 In this study, metformin administered at 500 mg twice daily dose had no effect on liver biochemistries or liver histology.
43. Intensive lifestyle modification improves aminotransferases and liver histology in children with NAFLD and thus should be the first line of treatment. (Strength – 2, Quality – B)
44. Metformin at 500 mg twice daily offers no benefit to children with NAFLD and thus should not be prescribed. The effect of metformin administered at a higher dose is not known. (Strength – 1, Quality – B)
45. Vitamin E 800 IU/day (RRR α–tocopherol) offers histological benefits to children with biopsy-proven NASH or borderline NASH but confirmatory studies are needed before its use can be recommended in clinical practice (Strength – 1,Quality – B)