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Keywords:

  • Idiopathic intracranial hypertension;
  • IIH;
  • pseudotumor cerebri

Summary

  1. Top of page
  2. Summary
  3. Introduction
  4. Methods
  5. Results
  6. Conclusions
  7. Conflict of Interest Statement
  8. Acknowledgements
  9. References

This study documents for the first time the extraordinary costs to take care of patients with a chronic, non-fatal, relatively rare disorder who have been incorrectly thought to have an insignificant and self-limiting illness. Idiopathic intracranial hypertension (IIH) occurs worldwide and in all racial groups and is found predominantly in obese women (∼90%) of childbearing age. Although the incidence of IIH is increasing as a result of the rapid increase in obesity, the disorder in general receives little recognition, and no recognition of the extensive burden of healthcare costs placed on patients, their families and society. We established for the first time both the prevalence of IIH in the USA and the direct and indirect costs of IIH using a prevalence-based model. IIH patients had an exceptionally high hospital admission rate of 38% (in 2007), a partial reflection of unsatisfactory treatment options. The total hospital costs per IIH admission in 2007 were four times greater than for a population-based per person admission. Total economic costs of IIH patients exceeded $444 million. Programmes designed to reduce obesity prior to and after diagnosis and better therapeutics will have a tremendous economic impact.


Introduction

  1. Top of page
  2. Summary
  3. Introduction
  4. Methods
  5. Results
  6. Conclusions
  7. Conflict of Interest Statement
  8. Acknowledgements
  9. References

Idiopathic intracranial hypertension (pseudotumor cerebri, IIH), a disorder of abnormal cerebrospinal fluid (CSF) hydrodynamics, occurs predominantly in obese women (∼90%) of childbearing age. The incidence of the disorder is 1–3 per 100 000 people in the general population but in obese women aged 20–40 years the rate is approximately 20 per 100 000 (1–5). Little is known about the disorder, nor has evidence-based medicine identified the most efficient and effective treatment path (6,7). Individuals are diagnosed with IIH after exhausting all possible causes (8). Patients without a detectable cause and fulfilling the Dandy criteria are diagnosed with IIH (4,9–12).

Patients present with an array of signs and symptoms including papilloedema, severe headache, visual disturbances that may include permanent loss of vision, which can severely limit functional independence and quality of life (8,13–15). Although the incidence is increasing as a result of the rapid increase in obesity, the disorder in general receives little recognition. Despite the ability to identify a specific, potential IIH target group based on characteristics of age, gender and often with affiliated abnormalities such as Polycystic Ovary Syndrome (PCOS), insulin resistance and congenital thrombophilias (16), few if any obesity preventive or interventional programmes have evolved.

Treatment for IIH is primarily palliative, beginning with medical therapy and progressing to surgical therapy (7,14). Carbonic anhydrase inhibitors such as acetazolamide, furosemide and topiramate are used to reduce CSF production. Surgical procedures, including optic nerve sheath decompression (ONSD), cerebal venous sinus stenting, and neurosurgical shunting, are often performed when patients do not respond to pharmaceutical interventions and vision loss is potentially eminent. For the majority, weight loss (and in extreme cases bariatric surgery) is prescribed in conjunction with medical and/or surgical treatments, and when successful may reduce IIH-related symptoms (17).

As IIH is a disorder with far-reaching consequences that have been largely overlooked by the medical community, healthcare institutions, industry and government, one way to promote public attention to and future research on IIH is to identify the economic costs of the disorder. In doing so, one can characterize the magnitude of the effects, both direct and indirect, that the disorder has on society, patients and their families, providing further incentive towards preventing obesity and finding better treatment options and a cure.

To date, this is the first study estimating the total costs of IIH.

Methods

  1. Top of page
  2. Summary
  3. Introduction
  4. Methods
  5. Results
  6. Conclusions
  7. Conflict of Interest Statement
  8. Acknowledgements
  9. References

Data sources

The data used in our analysis come from several sources. First, we used data from published sources to obtain an estimate on the incidence of IIH in the US population in 2007. We combined known incidence rates (2–5,18–20), along with estimates of the prevalence of obesity (21) and population projections (22) by gender and age to generate an estimate of the number of individuals in the USA suffering from IIH.

The second source of data was the Agency for Healthcare Research and Quality's Healthcare Cost and Utilization Project's (HCUP), Nationwide Inpatient Sample (NIS) (23), which was used to determine both hospital and procedure costs. The NIS is a hospital discharge database for the year 2005. The year 2005 was the last data available from HCUP at the time of this study. NIS is the largest all-payer in-patient care database containing approximately eight million hospital stays from 1000 hospitals sampled to approximate a 20% stratified sample of all US community hospitals. A synopsis of the NIS can be found on HCUP's website (23).

For a given hospital in the NIS, the data contain information on all hospital discharges by ICD9-CM codes. As such, it can be used to provide information on the direct medical expenses that arise because of the disorder. To examine in-patient IIH-related procedures, we utilized the ICD9-CM diagnostic code of pseudotumor cerebri 348.2. Similar to Curry et al. (24), to rule out cases of secondary IH such as brain tumours, a number of exclusionary diagnostic codes were removed. These codes were 190.x, 191.x, 192.x, 198.3, 198.4, 225.x, 237.x, 239.6, 239.7, 801–804, 850–854 and 430–437.

To establish the number of surgeries performed for IIH in the NIS 2005 data, ICD9-CM procedure codes for shunt placement (lumbar shunt 3.71, ventricular shunt 2.3x), shunt revision (lumbar shunts 3.97, ventricular 2.42), shunt removal (lumbar shunts 3.98, ventricular 2.43) and shunt exploration (54.95) were used. ONSD procedure codes used were 04.42 and 04.04. Unlike Curry et al.'s (24) exploration of the costs of IH, we included subtemporal decompression (procedure code 01.24) in our examination. Gastric bypass for IIH was established using DRG code 288 with inclusions and exclusionary criteria based on Zhoa and Encinosa (25). Inclusionary procedure codes were 4431, 4438, 4439, 4495, 4496, 4497, 4498, 445x and 4499 if found in combination with DRG 288. Exclusionary criteria were ICD9-CM codes 1500–1599, 2301–2309. All DRG 288 discharges were also checked to ensure that a diagnosis code of obesity was present (ICD9-CM codes 27801, 2780, 28900 and V778).

In addition we estimated discharge-related charges and physician costs from Medicare (26) data using CPT codes for shunting procedures (62220, 62223, 62230, 63740, 63741, 63744, 64746), ONSD (67570), subtemporal decompression (61340) and gastric bypass (43644, 43842). Finally, we use the consumer and producer price indices (series CPIAUCNS and NDU622110622110601, respectively) published by the US Bureau of Labor Statistics to convert 2005 dollars into equivalent 2007 dollars.

Our final source of data comes from the Intracranial Hypertension Registry (IHR). The IHR is co-sponsored by the Intracranial Hypertension Research Foundation and the Casey Eye Institute at the Oregon Health and Science University. It contains information gathered from individuals diagnosed with IH and their physicians. Patients are admitted to the IHR on a voluntary basis; however, medical information from at least one or more of the patients' physicians is required for admission and confirmation of diagnosis. The modified Dandy criteria (10) is used in the confirmation of IIH.

Patients were asked to complete a survey identifying their education and occupational characteristics, past and current earnings, IIH-related expenses and proxies for quality of life. One hundred and ninety-six patients completed the survey. For non-US residents (n = 4), monetary information provided in survey responses was converted to US dollars for the year in question using exchange rates provided by the St. Louis Federal Reserve Bank's economic database (27). The OHSU Institutional Review Board approved the survey.

Estimating the number of idiopathic intracranial hypertension cases (prevalence)

Table 1 Panel A shows general estimates of the US population by gender and age taken from the US Census Bureau's population projections for the year 2007. Because of the link between IIH and obesity (body mass index ≥30), we also collected data on the estimated prevalence of obesity in the USA by age and gender. These values were combined to generate point estimates for the number of obese and non-obese individuals, disaggregated by age and gender. Panel B used incidence rates from the established literature (2,6,8,14) to arrive at a point estimate for the number of new IIH cases in the USA for 2007. Given that age, gender and obesity have a differential impact on the occurrence of IIH, utilization of various incidence rates was appropriate (2,18–20,28–31). Panel C uses the traditional formula (prevalence = incidence × duration of disorder) to create point estimates for the prevalence of IIH in 2007.

Table 1.  Estimating the number of IIH cases (in 2007)
Panel A: obesity population estimates by age and gender (in thousands)
CategoryPopulationObesity prevalenceObese populationNon-obese population
Women, 0–1122 7860.154350919 277
Women, 12–145 9750.1649804 995
Women, 15–1910 5350.16417288 807
Women, 20–3428 8000.284817920 621
Women, 35–4421 0460.321675614 290
Women, 45–5422 0580.369813913 919
Women, 55–6416 7340.42170459 689
Women, 65–7410 3980.39340866 312
Women, 75 and older11 1520.23626328 520
Men, 0–1123 8250.177421719 608
Men, 12–146 2710.18311485 123
Men, 15–1911 1310.18320379 094
Men, 20–3428 8730.217626522 608
Men, 35–4420 5540.285585814 696
Men, 45–5421 2840.306651314 771
Men, 55–6415 3310.35554439 888
Men, 65–748 7630.31927955 968
Men, 75 and older7 0650.18012725 793
Panel B: IIH incidence estimates by age, gender and obesity*
PopulationIIH incidence per 1000IIH population
Obese women, 0–110.01139
Obese women, 12–140.02222
Obese women, 15–440.2003333
Obese women, 45 and older0.030657
Obese women total 4051
Non-obese women, 0–110.011212
Non-obese women, 12–140.022110
Non-obese women, 15 and older0.010821
Non-obese women total 1143
Obese men, 0–110.00417
Obese men, 12–140.0089
Obese men, 15 and older0.015454
Obese men total 480
Non-obese men, 0–110.00478
Non-obese men, 12–140.00841
Non-obese men, 15 and older0.003248
Non-obese men total 367
Women total 5194
Men total 847
Working age total 4575
Non-working age total 1466
Total new cases of IIH 6041
Panel C: IIH prevalence estimates by age, gender and obesity
PopulationIIH incidence (per year)IIH duration (years)IIH prevalence
  • *

    The same age groups were used in all calculations, and are consistent with those utilized in Panel A. The results for age groups of 15 years and older are reported as a single, aggregated category. A full set of these calculations are available from the lead author upon request.

  • IIH, idiopathic intracranial hypertension.

Women5 1944.322 334
Men8474.33 642
Working age4 5754.319 673
Non-working age1 4664.36 304
Non-obese1 5104.36 493
Obese4 5314.319 483
Total cases of IIH6 0414.325 976

Estimating the direct medical costs of idiopathic intracranial hypertension

To estimate the economic costs of IIH from a societal perspective, we used a multistep process. First, we used the 2005 NIS (the most recent available at the time of this study) to identify the direct medical costs associated with the disorder. Assuming population growth (which would also imply the growth of IIH) these numbers represent conservative estimates of the direct medical costs of the disorder.

Calculating lost wages due to idiopathic intracranial hypertension

Because IIH is a debilitating condition, it is often the case that an individual will not be able to perform his or her job-related duties, and thus will leave the workforce. Similarly, parents of young children with IIH may also incur lost wages in order to provide care for their children. As such, lost wages due to IIH-related symptoms are likely a significant component of the costs of the disorder. Lost wages were estimated in 2007 US dollars.

From the IHR survey we have information on respondent's earnings the last full year worked prior to IIH symptoms affecting work life, and earnings from last year (converted to 2007 US dollars). For those respondents who reported an occupational change because of IIH, we looked at the difference between what they earned the last full year they worked without IIH affecting their work lives and what they earned last year. For individuals who did not change occupations, we used the per cent of work missed due to IIH and earnings from last year to identify the amount of wages lost due to the disorder. These calculations allowed us to infer both the sample incidence with which respondents fell into these categories (no lost wages, lost wages but no occupational change, lost wages with an IIH-induced occupational change) as well as sample mean and median earnings for each of these groups. These values can be combined with our population estimates in Table 1 to infer the number and monetary value of lost earnings due to IIH.

Calculating non-medical idiopathic intracranial hypertension expenses

The last major component of the costs of IIH consists of non-medical expenses; i.e. transportation, child care and other ancillary costs that must be incurred as a direct consequence of the disorder itself, or in an attempt compensate for the impairments caused by the symptoms of the disorder. As the survey was administered in 2007 and asks about expenses in the current year we did not adjust for the effects of inflation.

Results

  1. Top of page
  2. Summary
  3. Introduction
  4. Methods
  5. Results
  6. Conclusions
  7. Conflict of Interest Statement
  8. Acknowledgements
  9. References

We estimate that there are 6041 cases of new IIH in the USA in 2007, 5194 of which are female and 4531 of which are obese (See Table 1 Panel C). Moreover, we estimate that 4575 individuals of working age (i.e. between the ages of 20 and 64) developed IIH in 2007. Of these working age individuals, 4027 are female. As the average duration of IIH is 4.3 years, we estimate that there are 25 976 total cases of IIH in 2007, 19 673 of which are of working age and 22 334 are female.

The most common surgical treatments for IIH were lumbar or ventricular shunts for CSF diversion (4). Table 2 Panel A contains the number and typical physician costs for a variety of shunting procedures used to treat IIH. In 2005 there were 1880 shunt surgeries, approximately half of which are new placements (899) and slightly less than half of which are revisions and removals (796). Slightly more than one thousand (1006) of these were ventricular shunts. The physician costs for each of these procedures are proportional to the number of shunting procedures performed. While the Medicare physician cost data were unavailable for ventricular shunt removals and shunt explorations (which makes these estimates conservative), the remaining 1626 procedures lead to nearly $1.25 million in physician costs in 2005, or in 2007 terms, nearly $1.33 million.

Table 2.  Estimating the direct medical costs of IIH
Panel A: total physician costs for shunt surgeries (in 2005, and in 2005 US dollars)
Type of surgeryNumber of proceduresTotal cost 2005 dollarsTotal cost 2007 dollars (CPI)Total cost 2007 dollars (PPI)
LP placement317$258 910$274 874$274 894
LP revision296$151 598$160 945$160 957
LP removals76$33 940$36 033$36 035
VP replacements582$535 526$568 546$568 587
VP revisions355$265 169$281 519$281 539
VP removals69UnknownUnknownUnknown
Shunt explorations185UnknownUnknownUnknown
Panel B: total (hospital and physical direct costs of IIH (in 2005, and in 2005 US dollars)
ProcedureCPT codes utilizedmean physician costs per procedureMean hospital costs per admissionNumber of admissionsTotal costs
  1. CPI, Consumer Price Index (series CPIAUCNS); IIH, idiopathic intracranial hypertension; LP, Lumboperitoneal Shunt; N/A, not applicable; PPI, Producer Price Index (series NDU622110622110601 for General Medical and Surgical Hospitals, Diseases and Disorders of the Nervous System); VP, Ventriculoperitoneal Shunt.

Shunts62220$712.37$34 6751696$60 016 980
62223    
63740    
63741    
63744    
63746    
62230    
Optic nerve sheath decompression67570$1074.64$34 55361$2 173 286
Subtemporal decompression61340$1312.41$97 95234$3 374 990
Gastric bypass43842    
43644$1358.69$34 263227$8 086 124
Non-surgicalN/AUnknown$18 5657803$144 862 695
Projected US total in 20059821$218 514 075
Projected US total in 2007 dollars using the CPI $231 987 431
Projected US total in 2007 dollars using the PPI $232 004 247

Panel B in Table 2 provides a more expansive set of costs based on hospital discharges we attribute to IIH (as opposed to procedures that are depicted in Panel A). As indicated in Panel B, the vast majority of patients (7803 out of 9821, or 79.5%) admitted for IIH were treated using non-surgical approaches. Shunting represents the most common invasive in-patient treatment for IIH with 1696 admissions and a mean cost in excess of $60 million. The number of admissions (1696) is less than the number of procedures performed (1880) because in some instances a single admission will result in several procedures performed. To keep our estimates conservative the physician costs associated with that admission reflect only the primary CPT code. In addition, a number of alternative and/or complementary treatment paths including bariatric surgery, subtemporal decompression and ONSD are also used. As most ONSD surgeries are carried out as out-patient, our number of ONSD is expectedly low. These together account for 322 admissions and generate costs of over $13.6 million.

These 9821 admissions amount to hospital costs of $218.5 million in 2005. Physician costs represent only about a 10th of this total, with the remainder of these costs accruing to hospitals. When we use the producer price index (series NDU622110622110601 for general medical/surgical hospitals treating diseases and disorders of the nervous system) or the consumer price index (series CPIAUCNS) published by the US Bureau of Labor Statistics to convert these values to 2007 dollars, we find that the total increases to approximately $232 million.

Our primary source for non-medical expenses comes from the IHR. Consistent with the established IIH literature, the vast majority of respondents were female (92%), of Caucasian and non-Hispanic heritage (92%) and either overweight or obese, both prior to diagnosis (68%) and at the time they apply to the IHR (80%). Nearly three-fourths of respondents have a high school or college degree, and over half (54%) have some vocational or college training. Eighty-two per cent of respondents were employed prior to being diagnosed with IIH, nearly half (46%) in professional occupations. Over 60% reported that their occupation has changed since their (or their children's) diagnosis with IIH, many reporting that they are unemployed or unable to work full time. All but three of the respondents reporting a career change identified IIH-related symptoms as the primary impetus for the change. There is an even distribution of respondents who report a given year as the last one in which they were able to work full time, free of IIH-related symptoms.

Table 3 contains the calculations of lost wages due to IIH. Of the 196 respondents, 135 individuals (69%) reported earnings and labour force participation prior to IIH. After converting all values to 2007 dollars, we find that these individuals exhibited median earnings of $33 037 per year. Ninety-three of these respondents reported lost wages due to IIH, 60 of which reported lost earnings and IIH-induced occupational changes (median: $23 816) and 33 reported lost earnings without an occupational changes (median: $1886).

Table 3.  Estimating lost wages due to IIH
Panel A: patient earnings in the IHR sample
Patient income*FrequencyMean incomeMedian incomeStandard deviation
Average earnings from the last year worked prior to IIH issues135$39 831$33 037$32 260
Average lost wages93$20 756$11 707$24 672
 Lost wages and no change in occupation due to IIH33$5 495$1 886$7 192
 Lost wages and a change in occupation due to IIH60$29 150$23 816$26 818
Panel B: estimating nationwide lost wages based on the IHR sample and no occupation change
Patient income*IncidenceNumberMean incomeMedian income
Average lost wages and no change in occupation due to IIH  $5 495$1 886
Incidence of lost wages in the sample0.17   
Projected number of individuals who incur or induce lost wages due to IIH (total number of individuals with IIH times IHR sample incidence) 4416  
Projected nationwide average lost wages due to IIH and no change in occupation  $24 265 920$8 328 576
Panel C: estimating nationwide lost wages based on the IHR sample and an occupation change
Patient income*IncidenceNumberMean incomeMedian income
Average lost wages and a change in occupation due to IIH  $29 150$23 816
Incidence of lost wages in the sample0.31   
Projected number of individuals who incur or induce lost wages due to IIH (total number of individuals with IIH times IHR sample incidence) 8053  
Projected nationwide average lost wages due to IIH and a change in occupation  $234 744 950$191 790 248
Panel D: estimating nationwide lost wages based on the IHR sample
Patient income*Mean incomeMedian income
  • *

    All monetary values are reported in 2007 US dollars.

  • Average lost wages in the IHR sample is a weighted mean of the average lost wages with and without employment changes due to IIH.

  • IHR, Intracranial Hypertension Registry; IIH, idiopathic intracranial hypertension.

Lost wages and no occupation change$24 265 920$8 328 576
Lost wages and an occupation change$234 744 950$191 790 248
Projected average lost wages due to IIH$259 010 870$200 118 824
Projected lost wages (national average wage)$204 304 565

After creating per person, per year lost wage estimates, we used this estimate to measure total lost wages for the US IIH population. From Table 1, prevalence is 25 976 cases of IIH. The data from the IHR suggest that 17% of these individuals, or 4416, have lost wages without changing occupations because of the disorder (Table 3, Panel B). If, at the median, these individuals lost just over $1886 per year, this implies that in 2007 US dollars, the average lost wages for this cohort equate to just over $8 million. Concomitantly, 31% of respondents lost wages and experienced an IIH-induced occupation change (Table 3, Panel C). At the median, these individuals lost just over $23 816 per year, implying that the lost wages for this cohort were about $191 million in 2007 dollars. In total, median lost wages due to IIH are in excess of $200 million (Table 3, Panel D). Combining this with the direct medical costs of the disorder, the total costs of IIH are over $430 million.

Fifty-six per cent of individuals completing the survey indicated that they incurred positive non-medical expenses. Thirty-seven per cent of individuals reported expenses ranging at or below $500.00, while nearly 6% report expenses between $500.01 and $1000.00 (Table 4). Seven per cent of respondents report expenses between $1000.01 and $2000.00, and 5% report expenses ranging from $2000.01 to $5000.00. Only three individuals (1.5%) report non-medical costs exceeding $5000 over the past year. We used the midpoints of the lower expenditure categories and the minimum value of the largest expenditure category, and found that the average individual in the IHR sample spends $873 per year on non-medical expenses. If there are 25 976 individuals in the USA affected by IIH, then the prevalence available in our sample imply that 14 547 individuals incur non-medical expenses in a given year. Multiplying our population projection times the mean non-medical expenses per individual yielded total non-medical expenses of over $12.6 million annually.

Table 4.  Estimating the non-medical costs of IIH
Patient costsMidpoint or point estimateNumber of registry patientsNon-medical costs
  1. IHR, Intracranial Hypertension Registry; IIH, idiopathic intracranial hypertension.

$0.01–$500.00$25073$18 250
$500.01–$1000.00$75011$8 250
$1000.01–$2000.00$150013$19 500
$2000.01–$5000.00$350010$35 000
$5000.00 and above$50003$15 000
None or no response 86 
Total indirect costs in the sample  $96 000
Average indirect costs per working individual (total indirect costs divided by 110)  $873
Incidence of indirect costs in the sample  0.56
Projected number of individuals with non-medical IIH costs (total number with IIH times IHR sample incidence)  14 547
Total projected non-medical costs due to IIH  $12 699 531

Conclusions

  1. Top of page
  2. Summary
  3. Introduction
  4. Methods
  5. Results
  6. Conclusions
  7. Conflict of Interest Statement
  8. Acknowledgements
  9. References

The purpose of this paper is to raise awareness of the high costs of rare diseases by providing some estimates of the cost of a single rare disorder. IIH was used to demonstrate and illustrate both direct and indirect costs. Using a variety of publicly available sources, we found that the economic costs of the disorder exceed $444 million annually (as measured in 2007 dollars) in the USA alone. Direct medical expenses play the dominant role in the costs of the disorder, followed by lost wages. However, even the smallest of these costs (non-medical expenses) is a very large number, at over $12.6 million.

To provide some perspective on these figures, in 2007 the USA spent an estimated $2.26 trillion on health care or $7439 per person (32). This per person cost represents total healthcare costs including professional office visits, out-patient care, dental services, nursing and home care, prescription drugs and medical equipment. US hospital care was $696.7 billion or approximately $2314 per person. The total hospital care cost per IIH admission in 2007 was $8931 or almost four times greater.

It is interesting to consider why the direct medical costs of IIH are so high, given that we estimate about 26 000 people are afflicted with the disorder. The information in Table 2 indicates that the answer can be traced to two related sources. First, the fact that fewer than 26 000 individuals generate over 9800 admissions clearly implies a relatively high usage of hospital services. Examining Panel A of Table 2, we can also infer that much of this activity comes from either (i) shunt revisions, removals and replacements or (ii) non-surgical treatments. The latter likely occur when the patient is admitted for diagnostic procedures, management and stabilization of symptoms, surgical complications, potential vision loss and/or other functional impairments.

When examining the direct medical costs of the disorder, either a large number of individuals were admitted to the hospital at least once each year or many patients had multiple admissions; ostensibly when those individuals had a recurrence of symptoms, surgical complications or a failed shunt. Thus if society devoted greater effort towards finding a cure for the disorder, or as a second best solution, optimal treatment paths including management of obesity, many of these IIH-related re-admissions could be avoided.

As with all studies, our analysis is subject to a number of limitations. First, our estimates are specifically designed to be conservative, and thus should underestimate the true costs of IIH. Moreover, we restricted our analysis to those costs that were most apparently quantifiable. Other costs were only indirectly included by the extent to which they indicate additional costs. Unplanned changes in a career, for example, indicate a reduction in the quality of one's life. As our goal is to provide some conservative estimates, this is not included in this study. However, future research that added these costs to those included in our study would likely find the costs of the disorder to be much higher. Finally, a portion of our data comes from a sample of the IHR. As with most surveys based on fixed populations such as the IHR, sample selection may be an issue. We have made the case that our data are consistent with the population of IIH sufferers at large, and if there is a bias it does so in a way that makes the estimates conservative.

One difficulty associated with estimating the prevalence of IIH by gender, age and obesity is a paucity of IIH incidence rates for each of these cohorts. As such, we are forced to employ a pair of additional assumptions, which are consistent with what is known about the disorder. First, there are no known IIH incidence rates for women over the age of 45, which are stratified by whether an individual is obese. Because obesity is thought to disproportionately increase the likelihood of IIH, we assume that the incidence among obese women is three times that of the corresponding non-obese rate. Second, there are no available estimates of IIH for men, especially when stratified by whether a man is obese. As both obesity and being female are thought to increase the likelihood of developing IIH, we assume that the incidence among obese men is roughly half that of obese women and five times that of non-obese men. While these assumptions are admittedly ad hoc, an examination of Table 1 suggests that the estimated number of individuals in these categories suffering from IIH is relatively small. As such, even if our assumptions are improper, the error introduced from these assumptions is unlikely to significantly impact our overall estimates of the disease cost.

Finally, the numbers predicted from the IHR may be biased upward as the sociodemographic information from the IHR implies that a majority of individuals afflicted with IIH have relatively high levels of education and many work/ed in professional settings prior to being diagnosed with the disorder. As a robustness check, we also measured the average wage loss if IIH sufferers on average earned the national average but lost proportionately similar income shares. From Table 3 Panel A, the weighted average lost earnings was $20 756 of an average pre-impact earnings of $39 831, or about 52% resulting in $259 010 870 total estimated loss. With the national average wage of $31 510 (US Bureau of Labor and Statistics: http://www.bls.gov/news.release/archives/realer_01162008.pdf), an average loss is $16 385. Based on the estimated number of individuals losing income from the IHR, 12 469 people can be expected to incur this loss, producing a total loss of $204 304 565. As this number is greater than the median income figure ($200 118 824) provided by the IHR data, the latter impact is a more conservative estimate of lost income. As such, we used the median lost wage estimate produced solely by using the IHR data to keep our total estimates conservative.

Currently little is known about IIH, but the costs of this disorder are quite substantial. As such, it may be very useful for the medical and policy-making communities to direct efforts towards finding ways to better treat and manage the disorder, including efforts to eliminate obesity, in order to reduce some of these costs.

Conflict of Interest Statement

  1. Top of page
  2. Summary
  3. Introduction
  4. Methods
  5. Results
  6. Conclusions
  7. Conflict of Interest Statement
  8. Acknowledgements
  9. References

The authors declare that they have no conflicts or competing interests.

Acknowledgements

  1. Top of page
  2. Summary
  3. Introduction
  4. Methods
  5. Results
  6. Conclusions
  7. Conflict of Interest Statement
  8. Acknowledgements
  9. References

We acknowledge the expert help and support of Sara Loboy, B.S., research coordinator at the IHR, and from the volunteer staffs of the IHR and OHSU. We are particularly indebted to volunteer Ralpha Newton for encouragement and her tireless effort.

References

  1. Top of page
  2. Summary
  3. Introduction
  4. Methods
  5. Results
  6. Conclusions
  7. Conflict of Interest Statement
  8. Acknowledgements
  9. References