To evaluate the prevalence, clinical associations, and outcome of antiphospholipid syndrome (APS) nephropathy in patients with systemic lupus erythematosus (SLE) and antiphospholipid antibodies (aPL) and in SLE patients without aPL.
To evaluate the prevalence, clinical associations, and outcome of antiphospholipid syndrome (APS) nephropathy in patients with systemic lupus erythematosus (SLE) and antiphospholipid antibodies (aPL) and in SLE patients without aPL.
Kidney biopsy specimens obtained from 81 patients with aPL (18 of whom had APS) and 70 patients without aPL were retrospectively examined for the presence of APS nephropathy. Clinical and serologic data obtained at the time of kidney biopsy and during a mean followup of 7 years were recorded. In cases for which serial kidney biopsy specimens were available, the evolution of APS nephropathy was examined.
APS nephropathy existed in 39.5% of patients with aPL, compared with only 4.3% of patients without aPL. APS nephropathy was associated with both lupus anticoagulant and anticardiolipin antibodies. Among aPL-positive SLE patients, APS nephropathy was found in two-thirds of those with APS and in one-third of those without APS. A strong association between APS nephropathy and the presence of arterial thrombosis and livedo reticularis was noted. Patients with APS nephropathy had a higher frequency of hypertension and elevated serum creatinine levels at the time of kidney biopsy but did not have a higher frequency of renal insufficiency, end-stage renal disease, or death at the end of followup. Serial kidney biopsy specimens were available from 11 patients and showed progression of APS nephropathy lesions. During followup, manifestations of APS (especially arterial thromboses) developed more frequently in the SLE/non-APS patients with APS nephropathy than in those without APS nephropathy.
Among patients with SLE, APS nephropathy occurs almost exclusively in those with aPL, suggesting an important role of aPL in the pathogenesis of APS nephropathy. Patients with APS nephropathy develop hypertension, raised serum creatinine levels, and progression of histologic lesions, all of which are associated with a poor renal outcome. Manifestations of APS also tend to develop in these patients. APS nephropathy should be included in the APS classification criteria, and the use of appropriate anticoagulant therapy should be tested.
The antiphospholipid syndrome (APS) is a multisystem disease characterized by arterial and venous thromboses, pregnancy morbidity, and the presence of antiphospholipid antibodies (aPL), namely anticardiolipin antibodies (aCL) and lupus anticoagulant (LAC) (1, 2). APS is classified as primary or classified as secondary when it occurs in the context of other underlying disorders, mainly systemic lupus erythematosus (SLE) (3). Antiphospholipid antibodies are detected in ∼30–40% of patients with SLE; arterial or venous thrombosis will develop in nearly one-third of these patients (1, 4). Thrombosis may occur at any vascular site and in any organ system. However, the intrarenal vascular involvement in association with APS was poorly recognized until recently. A possible explanation is that kidney biopsies were rarely performed in patients with primary APS, and the majority of studies in SLE focused on immune complex glomerulonephritis rather than renal microangiopathy.
The most commonly reported intrarenal vascular lesion in patients with APS (primary or secondary) (5–10) and in patients with SLE and aPL (11–17) is thrombotic microangiopathy (TMA), which is characterized by the presence of fibrin thrombi in glomeruli and/or arterioles. In a recent multicenter retrospective study, Nochy et al examined kidney biopsy specimens obtained from 16 patients with primary APS (18). All of the patients had vasoocclusive lesions characterized by acute thromboses (TMA) and chronic vascular lesions such as fibrous intimal hyperplasia (FIH) of interlobular arteries, recanalizing thrombi in arteries and arterioles, fibrous occlusions, or focal cortical atrophy (FCA). Daugas et al observed that the above-mentioned histologic lesions, defined as APS nephropathy, exist also in SLE—especially in SLE patients with secondary APS—independently of lupus nephritis (19). An association of APS nephropathy with APS (mainly with arterial thrombosis and abortions) and LAC, but not with aPL, was observed. In both of these studies, systemic hypertension was the main clinical manifestation of APS nephropathy.
The purpose of the current study was to evaluate the following: 1) the presence of APS nephropathy in kidney biopsy specimens obtained from SLE patients with or without aPL, in order to assess any association between APS nephropathy and aPL, 2) clinical and laboratory associations with APS nephropathy, 3) the renal prognosis of patients with APS nephropathy, 4) the evolution of APS nephropathy in patients who underwent repeated kidney biopsies, and 5) any tendency of SLE/non-APS patients with APS nephropathy to develop APS during long-term followup.
The study group comprised all patients with SLE and biopsy-proven renal involvement (n = 151) who were followed up on a regular basis at the Department of Pathophysiology and for whom at least 2 measurements of aPL were performed before or at the time of kidney biopsy. The patients were categorized as those with aPL (n = 81), including those with APS (n = 18), and those without aPL (n = 70). All of the patients fulfilled at least 4 of the American College of Rheumatology criteria for the diagnosis of SLE (20) at the time of kidney biopsy. APS was diagnosed according to the Sapporo criteria (2). Patients who had aPL but did not have APS were defined as SLE/non-APS patients with aPL.
The criteria for exclusion from the study were other potential causes for renal microangiopathy, such as systemic sclerosis, malignant hypertension, thrombotic thrombocytopenic purpura, hemolytic uremic syndrome, postpartum renal failure, preeclampsia, diabetic nephropathy, human immunodeficiency virus infection, chemotherapy, or cyclosporine therapy.
The kidney biopsies were performed from 1987 to 2002 in patients who had either proteinuria (urinary protein concentration ≥500 mg/dl), abnormal urinary sediment, or an elevated serum creatinine level. The biopsy specimens were retrospectively studied, using light microscopy, by 2 renal pathologists who had no knowledge of the clinical and laboratory features of the patients. The World Health Organization (WHO) classification of lupus glomerulonephritis (21) and the WHO activity and chronicity index scores (22) were reevaluated. The immunofluorescence microscopy findings as described in the initial reports of the kidney biopsies were accepted. As in previously published reports (18, 19), APS nephropathy was diagnosed when at least 1 of the following lesions was detected: TMA, characterized by the presence of fibrin thrombi in arterioles and/or glomeruli (acute lesion), or myofibroblastic intimal cellular proliferation leading to intimal thickening of interlobular arteries [FIH]), organized thrombi with or without recanalization, fibrous arterial and arteriolar occlusion, and subcapsular zone with FCA (chronic lesions). In cases of APS nephropathy for which serial kidney biopsy specimens were available, the evolution of histologic lesions was examined.
The following demographic, clinical, and serologic data obtained at the time of the first kidney biopsy were collected from the medical records: age, sex, duration of SLE (time from the diagnosis of SLE to the end of followup), time from the kidney biopsy to the end of followup, pregnancy morbidity as defined by the Sapporo criteria, arterial or venous thrombosis, pulmonary embolism, arthritis, malar or discoid rash, mouth ulcers, photosensitivity, serositis, Raynaud's phenomenon, livedo reticularis, systemic hypertension (systolic blood pressure >140 mm Hg, diastolic blood pressure >90 mm Hg), raised serum creatinine level (>1.4 mg/dl), proteinuria, nephrotic syndrome (urinary protein concentration >3 gm/24 hours), leukopenia (white blood cell count <4,000/mm3), thrombocytopenia (platelet count <100,000/mm3), autoimmune hemolytic anemia, hyperlipidemia, low C3 or C4 levels, antibodies to extractable nuclear antigens (ENA) Ro, La, Sm, and U1 nRNP, anti-DNA antibodies, LAC, and IgG and IgM aCL. Treatment with cyclophosphamide, azathioprine, hydroxychloroquine, or corticosteroids, the duration of therapy with steroids, aspirin, coumarin, antihypertensive drugs, and estrogens, and the patient's use of cigarettes or alcohol were also recorded.
The duration of followup for each patient was measured from the time of the kidney biopsy to the last visit or the beginning of dialysis. The frequency of patient visits was every 3–4 months. The end of followup was December 2002. The following parameters were recorded during this period: arterial or venous thrombosis, pregnancy morbidity, serum creatinine levels, and renal insufficiency (creatinine clearance <75 ml/minute) at the end of followup, end-stage renal disease (ESRD) requiring dialysis or renal transplantation, and death.
The renal tissues obtained by needle biopsy were fixed in Bouin's fluid or in 10% neutral buffered formalin, gradually dehydrated, and embedded in paraffin. Paraffin sections (2–3μ) were stained with eosin and hematoxylin, periodic acid–Schiff (PAS), silver methenamine, Masson's trichrome stain, and elastic–Van Gieson stain. Small portions of fresh renal tissue were snap-frozen and stored at −80°C. Four-micrometer cryostat sections were incubated with fluorescein-conjugated rabbit antisera against human IgG, IgA, IgM, C1q, C3, C4, κ and λ light chains, and fibrinogen and were examined by direct immunofluorescence. All of the antisera were purchased from Dako Cytomation (Glostrup, Denmark).
In the cases in which TMA was demonstrated on light microscopy, additional paraffin sections were studied for fibrinogen deposits by immunohistochemistry. After dewaxing and dehydration, paraffin sections were transferred to Tris buffered saline (TBS) and subjected to antigen retrieval in a microwave oven for 15 minutes. After rinsing in distilled water for 5 minutes, the sections were incubated with peroxidase-blocking solution (3% H2O2) for 10 minutes, rinsed in distilled water for 5 minutes, and washed in TBS for 10 minutes. Furthermore, they were incubated with polyclonal anti-human fibrinogen serum for 30 minutes at room temperature (1:1,500; Dako) and washed in TBS for 10 minutes. EnVision horseradish peroxidase (Dako) was then applied for 30 minutes, followed by a TBS bath for 10 minutes. Sections were incubated with diaminobenzidine tetrahydrochloride for 10 minutes and rinsed in distilled water for 5 minutes. PAS was used as a counterstain. Control sections were treated with nonimmune gamma globulin.
Antinuclear and anti-DNA antibodies, ENA, C3, and C4 were assessed according to standard methods. Determination of IgG and IgM antibodies to aCL was performed with an enzyme-linked immunosorbent assay, as previously described (23). Cardiolipin (50 μg/ml) in ethanol (Sigma, St. Louis, MO) was used as antigen on polystyrene microtiter plates (Nunc, Naperville, IL), which were left to dry overnight at 4°C. After washing with phosphate buffered saline, the nonspecific binding sites were blocked by 10% bovine serum in phosphate buffered saline. LAC was assayed by activated thromboplastin time, kaolin clotting time, or dilute Russell's viper venom time (24). The detection of LAC in medium or high titers of aCL at least 2 times, 6 weeks apart (2), before or at the time of kidney biopsy, was required.
The associations between categorical variables were tested using Fisher's exact test or the chi-square test when required. In addition, the odds ratios (ORs) with the corresponding 95% confidence intervals (95% CIs) were determined using binary logistic regression. Variables that were statistically significant in univariate models were considered in multivariate regression models built on backward elimination according to the likelihood regression criteria. For continuous variables, the comparisons were carried out using the t-test for 2 independent samples or the Mann-Whitney U test for non-normal data. P values less than 0.05 were considered significant. The analysis was performed using advanced SPSS software version 11 (2001; SPSS, Chicago, IL).
This series consisted of 151 white patients with SLE (132 women and 19 men). The mean (±SD) age of patients at the time of kidney biopsy was 31.56 ± 13.18 years (range 9–66 years), and the mean (±SD) duration of followup was 7.07 ± 3.7 years (range 1–15 years). The mean (±SD) duration of disease before the kidney biopsy in SLE patients with aPL and those without aPL was 5.3 ± 4.1 years and 4.47 ± 3.78 years, respectively (P = 0.24). In aPL-positive patients, positivity persisted during the entire followup period. The frequency of lupus-related manifestations (arthritis, rash, mouth ulcers, photosensitivity, serositis, Raynaud's phenomenon, leukopenia, thrombocytopenia, autoimmune hemolytic anemia) did not differ between aPL-positive and aPL-negative patients. In addition, hypertension, serum creatinine levels, proteinuria, nephrotic syndrome, or renal insufficiency, and treatment with cyclophosphamide, azathioprine, hydroxychloroquine, or corticosteroids, as well as the duration of corticosteroid treatment were not statistically different between patients who were aPL positive and those who were aPL negative (P > 0.05).
APS nephropathy was diagnosed in 32 (39.5%) of 81 SLE patients with aPL, compared with only 3 (4.3%) of the 70 SLE patients without aPL (P < 0.01). The prevalence of APS nephropathy in SLE patients with secondary APS and in SLE/non-APS patients with aPL was 67% and 31.7%, respectively. A strong association between APS nephropathy and APS, LAC, aCL, and livedo reticularis was noted (Table 1). Twenty-three of 151 patients with SLE (15.2%) had acute APS nephropathy, while 31 of 151 patients (20.5%) had chronic APS nephropathy. The mean (±SD) disease duration before kidney biopsy in patients with and those without chronic APS nephropathy was 6.45 ± 5.12 years and 4.72 ± 4.68 years, respectively (P = 0.125). The most common histologic lesions were TMA, FIH, and FCA. All of the patients with chronic APS nephropathy had FIH. Four patients had only acute lesions.
|Patients without APSN (n = 116)||Patients with APSN (n = 35)||Univariate analysis, OR (95% CI)||Multivariate analysis, OR (95% CI)|
|APS||6 (5.2)||12 (34.3)||9.6 (3.3–28.1)†||Not selected|
|Lupus anticoagulant||4 (3.4)||16 (45.7)||23.6 (12.8–43.5)†||11.46 (3.1–41.7)†|
|Anticardiolipin antibodies||51 (44.0)||30 (85.7)||7.7 (2.8–21.1)†||5.7 (1.8–17.8)†|
|Livedo reticularis||29 (25)||20 (57.1)||4.0 (1.8–8.8)†||Not selected|
|Hypertension||42 (36.2)||27 (77.1)||4.1 (1.6–10.6)†||4 (1.5–8.6)‡|
|Increased serum creatinine level||19 (16.3)||17 (48.5)||2.6 (1.0–6.5)‡||Not selected|
The group of SLE patients without aPL included a very small number of patients with APS nephropathy (n = 3); therefore, this group was not considered in the subsequent statistical analyses. Two of these 3 patients had high IgG aCL titers during followup but only on one measurement, which was not reproduced on several subsequent examinations.
Table 2 shows the demographic, clinical, and laboratory characteristics of SLE patients with aPL who were diagnosed with or without APS nephropathy at the time of kidney biopsy. The mean age, duration of lupus, and mean time from renal biopsy were not statistically different between the 2 groups. A significant association between APS nephropathy and arterial thrombosis (especially stroke), pulmonary embolism, livedo reticularis, and LAC was documented. Patients with pulmonary embolism were not included in the group with venous thrombosis, because they had no findings of deep vein thrombosis on Doppler venous ultrasonography and/or venography. No statistically significant correlation was noted between APS nephropathy and venous thrombosis, pregnancy morbidity, lupus clinical characteristics (arthritis, rash, mouth ulcers, photosensitivity, serositis, Raynaud's phenomenon), and serologic findings (leukopenia, thrombocytopenia, autoimmune hemolytic anemia, anti-DNA antibodies, ENA antibodies, low C3 or C4 levels, aCL, hyperlipidemia) (P > 0.05). There also was no difference between patients with and those without APS nephropathy regarding treatment with azathioprine (P = 0.572), hydroxychloroquine (P = 0.785), cyclophosphamide (P = 0.058), aspirin (P = 0.471), or corticosteroids (P = 0.805), and the duration of steroid therapy (P = 0.67). The mean ± SD duration of aspirin therapy in patients with and those without APS nephropathy was 3.0 ±1.4 years and 3.3 ± 1.8 years, respectively (P = 0.56). The duration of anticoagulant therapy in SLE patients with secondary APS was 7.6 ± 4.3 years.
|Characteristic||Patients without APSN (n = 49)||Patients with APSN (n = 32)||Univariate analysis, OR (95% CI)||Multivariate analysis, OR (95% CI)|
|Age at biopsy, mean ± SD years||29.5 ± 13.3||34.3 ± 13||–||–|
|SLE duration, mean ± SD years||10.4 ± 6.7||12.5 ± 7.3||–||–|
|Time from renal biopsy to end of followup, mean ± SD years||6.3 ± 3.7||7.1 ± 4.1||–||–|
|Arterial thrombosis||4 (8.2)||11 (34.4)||5.9 (1.7–20.7)†||Not selected|
|Stroke||2 (4.1)||8 (25.0)||7.8 (1.5–39.8)†||Not selected|
|Pulmonary embolism||1 (2.0)||5 (15.6)||8.9 (1–80.1)†||Not selected|
|Abortion||1 (2.0)||3 (9.4)||5.0 (0.5–5.0)||–|
|Venous thrombosis||3 (6.1)||3 (9.4)||1.6 (0.3–8.4)||–|
|Livedo reticularis||16 (32.7)||19 (59.4)||3.0 (1.2–7.6)†||Not selected|
|Hypertension||17 (34.7)||25 (78.1)||6.7 (2.4–18.7)†||6.7 (2.1–21.2)†|
|↑serum creatinine level||8 (16.3)||14 (43.8)||4.0 (1.4–11.2)†||Not selected|
|Proteinuria||44 (89.8)||28 (87.5)||0.8 (0.2–3.2)||–|
|Nephrotic syndrome||9 (18.4)||11 (34.4)||2.3 (0.8–6.5)||–|
|Lupus anticoagulant||4 (8.2)||16 (50.0)||12 (3.5–41.5)†||8 (2.1–30.3)†|
|Anticardiolipin antibodies||49 (100)||30 (93.8)||–||–|
Acute APS nephropathy was observed in 21 patients, and chronic APS nephropathy was demonstrated in 28 patients (Figures 1–5). Seventeen patients had both acute and chronic lesions. FIH and FCA were the most frequently observed chronic vascular lesions, detected in 28 and 17 patients, respectively. No association between APS nephropathy and the WHO classes of lupus nephritis was detected. The kidney biopsy specimens obtained from patients with APS nephropathy (n = 32) were classified according to WHO criteria as follows: class II, 4 specimens (12.5%); class III, 8 specimens (25%); class IV, 9 specimens (28.1%); class V, 9 specimens (28.1%); and class VI, 2 specimens (6.9%) (χ2 = 6.1, P = 0.20). The WHO activity and chronicity index scores also were not different between the 2 groups (P = 0.31 and P = 0.06, respectively). No association between chronic APS nephropathy and the WHO chronicity index score was observed (P = 0.057).
At the time of kidney biopsy, the patients with APS nephropathy more frequently had systemic hypertension and raised serum creatinine levels than did the patients without APS nephropathy (Table 2). The mean ± SD duration of hypertension in patients with and those without APS nephropathy was 6.96 ± 4.5 years and 6.25 ± 4.5 years, respectively (P = 0.62). Hypertension was found to be associated with acute APS nephropathy, livedo reticularis, and LAC, but not with the WHO class of lupus glomerulonephritis (Table 3). The mean ± SD serum creatinine level in patients with and those without APS nephropathy was 1.33 ± 0.51 mg/dl and 0.98 ± 0.45 mg/dl, respectively (P = 0.024). The mean ± SD creatinine level in the patients with APS nephropathy who had raised serum creatinine levels at the time of kidney biopsy was 1.58 ± 0.18 mg/dl. Elevated creatinine levels at the time of kidney biopsy were associated with chronic APS nephropathy and LAC (Table 4). The occurrence of proteinuria or nephrotic syndrome was not different between patients with and those without APS nephropathy (Table 2).
|Characteristic||Patients without hypertension (n = 39)||Patients with hypertension (n = 42)||Univariate analysis, OR (95% CI)||Multivariate analysis, OR (95% CI)|
|Acute APSN||5 (12.8)||16 (38.1)||4.2 (1.4–12.9)†||Not selected|
|Chronic APSN||13 (33.3)||15 (35.7)||1.1 (0.7–1.8)||–|
|FCA||3 (7.7)||14 (33.3)||6.0 (3.0–11.9)†||Not selected|
|Increased serum creatinine level||3 (7.7)||19 (45.2)||9.9 (2.6–37.3)‡||9.6 (2.1–16.7)‡|
|Livedo reticularis||12 (30.8)||23 (54.8)||2.7 (1.1–6.8)†||Not selected|
|Lupus anticoagulant||4 (10.2)||16 (38.1)||5.2 (1.6–17.5)‡||Not selected|
|II||4 (10.2)||6 (14.3)||–||–|
|III–IV||27 (69.2)||24 (57.1)||0.6 (0.2–2.4)||–|
|V–VI||8 (20.5)||12 (28.6)||1.3 (0.4–4.0)||–|
|Characteristic||Patients without raised serum creatinine (n = 59)||Patients with raised serum creatinine (n = 22)||Univariate analysis, OR (95% CI)||Multivariate analysis, OR (95% CI)|
|Acute APSN||12 (20.3)||9 (40.9)||2.7 (0.9–7.8)||–|
|Chronic APSN||13 (22.0)||15 (68.2)||4.8 (1.8–15.3)†||Not selected|
|FCA||7 (11.9)||10 (45.5)||6.2 (2.0–19.6)†||5.8 (1.7–19.8)†|
|Livedo reticularis||26 (44.1)||9 (40.9)||0.9 (0.3–2.4)||–|
|LAC||10 (17.0)||10 (45.5)||4.0 (1.4–11.8)‡||Not selected|
|II||7 (11.9)||3 (13.6)||–||–|
|III–IV||40 (67.8)||11 (50.0)||0.6 (0.1–2.9)||–|
|V–VI||12 (20.3)||8 (36.4)||1.9 (0.6–6.3)||–|
At the end of followup, no difference was detected between the 2 groups in the frequency of renal insufficiency and ESRD (OR 2.0 [95% CI 0.6–5.9], P = 0.26 and OR 0.3 [95% CI 0.04–3.4], P = 0.33, respectively). Renal insufficiency at the end of the followup period was strongly associated with the presence of hypertension and a raised serum creatinine level at the time of kidney biopsy (OR 6.6 [95% CI 2.3–12.7], P = 0.009 and OR 8.7 [95% CI 2.7–18.6], P < 0.001, respectively). Four patients with APS nephropathy and 3 without APS nephropathy died.
During the followup period, 11 of 32 patients with APS nephropathy had serial kidney biopsies performed (8 patients had 2 procedures and 3 patients had 3 procedures). The mean ± SD time between the first biopsy and the last biopsy was 6.3 ± 3.4 years (range 2–12 years). Table 5 shows the number of patients in whom the status of lesions was the same, better, or worse at followup, as well as the number of patients with new histologic lesions on sequential kidney biopsy specimens and the number of patients with no detectable lesions on either the initial or sequential specimens.
|Histologic lesion||None†||Lesion status at followup||New lesions‡|
|Fibrous intimal hyperplasia||2||3||0||0||6|
|Arterial occlusive lesions||8||0||0||0||3|
|Focal cortical atrophy||3||0||1||4||3|
|Global glomerular sclerosis||0||0||0||8||3|
|Hyalinosis of arterioles||4||0||2||2||3|
|Concentric (onion skin–like) fibrosis of arterioles||8||1||0||0||2|
|Mural myocytic hyperplasia of arterioles||11||0||0||0||3|
During the followup period, thrombosis developed in 7 (35%) of 20 patients with APS nephropathy, compared with 4 (9%) of 43 patients without APS nephropathy (P = 0.04). The patients with APS nephropathy had thrombosis at the arterial level (4 had stroke, 2 had pulmonary embolism, and 1 had acute myocardial infarction), although deep vein thrombosis developed in the patients without APS nephropathy. Among patients with APS nephropathy, no difference was found between those with thrombosis (n = 7) and those without thrombosis (n = 13) regarding the presence of additional risk factors for thrombosis such as nephrotic syndrome, hypertension, chronic renal failure, hyperlipidemia, treatment with estrogens or corticosteroids, and the duration of corticosteroid treatment (P > 0.05). None of these 7 patients with thrombosis smoked cigarettes or abused alcohol. Four of the 7 patients were receiving aspirin treatment at the time of thrombosis, but none was being treated with coumarin. During followup, thrombosis did not develop in any of the SLE patients without aPL.
In the present study, we examined the prevalence and the long-term outcome of APS nephropathy in 151 SLE patients with or without aPL. This report is the first to address the histologic evolution of APS nephropathy lesions on serial kidney biopsy specimens and the clinical evolution to APS in SLE/non-APS patients with APS nephropathy. APS nephropathy was documented independently of lupus glomerulonephritis in approximately two-thirds of SLE patients with secondary APS and one-third of SLE/non-APS patients with aPL but in only 3 of 70 SLE patients without aPL. APS nephropathy was strongly associated with both aCL and LAC, suggesting that aPL play a direct role in the development of APS nephropathy.
In this study, the sample size was quite small; therefore, the results of the multivariate analyses should be interpreted with caution. Unavoidably, our study could not have had enough power to detect modest differences in clinical, histologic, and laboratory findings between the groups, yet we were able to determine strong associations with large ORs for specific clinical, laboratory, and histologic parameters.
The most frequently observed pathologic lesions were TMA, FIH, and FCA. TMA is characterized by fibrin thrombi in the glomeruli and/or small arterioles in the absence of vascular immune deposits or inflammatory cells. The appearance of TMA lesions is similar to the changes observed in thrombotic thrombocytopenic purpura and the hemolytic uremic syndrome, entities occasionally occurring in the context of SLE (25, 26). When making a diagnosis of APS nephropathy, the clinical context must be considered rather than relying only on biopsy criteria. Patients with SLE who had features of the above-mentioned disorders were excluded from the current study. In SLE, TMA has been associated with the presence of LAC and/or aCL but not with the WHO class of lupus nephritis. In several studies, it has also been associated with a worse renal prognosis (13, 17, 26). TMA was the main renal vascular lesion observed in sporadic cases of primary APS. D'Agati et al reported the presence of TMA in the kidney biopsy specimens obtained from 2 patients with primary APS and 1 patient with SLE (5). Kincaid-Smith and coworkers (11) reported the occurrence of TMA and FIH in 12 women with aPL and postpartum renal failure (8 with primary APS, 4 with SLE). Amigo et al documented the presence of TMA, FIH, and glomeruli ischemia in 5 patients with primary APS and renal involvement (6).
In 1999, a group of French investigators described for the first time the presence of APS nephropathy in patients with primary APS (18). In 2002 the same group described the presence of APS nephropathy in patients with SLE, especially those with secondary APS (19). The latter elegant study examined 24 SLE patients with APS, 52 SLE/non-APS patients with aPL, and a small number of patients without aPL (n = 20). APS nephropathy was observed in 63%, 22%, and 15% of these patients, respectively. An association of APS nephropathy was noted with APS and LAC but not with aPL. The discrepancy between these results and ours, which showed a strong correlation of APS nephropathy with both LAC and aCL, may be explained by the fact that APS was associated with LAC but not with aCL in the above-mentioned series. In our study, only 2 of 32 aPL-positive patients with APS nephropathy were negative for aCL.
Concerning the renal prognosis of the patients with APS nephropathy, a high prevalence of hypertension was found, which is consistent with previous reports (5, 11, 14, 16, 18, 19, 26). Regarding the possibility that features of APS nephropathy are secondary to hypertension, it could be argued that the histologic lesions described above developed in several patients without hypertension. In addition, hypertension was found to be associated with acute and chronic APS nephropathy, livedo reticularis, and LAC, but not with the WHO class of lupus nephritis. An association of APS nephropathy with raised serum creatinine levels but not with proteinuria, nephrotic syndrome, renal insufficiency, or ESRD was also documented. In previous studies, the prevalence of proteinuria, nephrotic syndrome, chronic renal failure, or elevated serum creatinine levels in patients with SLE and/or APS and renal vascular lesions was variable (17–19, 26–28).
Given that progression of renal histologic findings in patients with SLE has been correlated with a poor renal prognosis, the evolution of APS nephropathy findings on repeated kidney biopsy specimens was examined. A progression of the acute thrombotic lesions to chronic proliferative, obstructive, and fibrotic forms was observed. The presence of TMA in the first biopsy specimen was usually followed by the appearance of chronic lesions such as FIH, arteriolar occlusions, FCA, or sclerotic lesions in the second or third biopsy specimen. Daugas et al reported that the higher age of patients with chronic APS nephropathy suggests that the chronic lesions develop later, probably originating as acute APS nephropathy (19). Kincaid-Smith et al reported biopsy specimens showing fibrin thrombi in glomerular arterioles and interlobular arteries at the time of acute renal episodes, and ischemic glomeruli with double contours, arteries narrowed by recanalizing thrombi, and cellular or fibroelastic intimal proliferation in specimens obtained at repeated biopsies months or years later (11).
In the literature, the presence of hypertension and elevated creatinine levels at the time of kidney biopsy is associated with a worse renal outcome. In our series, however, no difference was observed in the frequency of renal insufficiency or ESRD at the end of followup between patients with and those without APS nephropathy. This discrepancy could be explained by the fact that patients with APS nephropathy had mild renal insufficiency at the time of kidney biopsy (the mean ± SD creatinine level in patients with raised serum creatinine levels at the time of kidney biopsy was 1.58 ± 0.18 mg/dl), which was probably reversible with the immunosuppressive and/or anticoagulant treatment. Twelve (37.5%) of 32 patients with APS nephropathy had secondary APS; these patients had been receiving anticoagulant therapy continuously from the time of kidney biopsy. Anticoagulant therapy could influence the renal outcome. The fact that only 1 of 11 patients with progression of histologic lesions on sequential kidney biopsy specimens had secondary APS (this patient had been receiving anticoagulation treatment) may support the above hypothesis. Unfortunately, the small number of patients prevents drawing any definite conclusion regarding the potential role of anticoagulant therapy on renal prognosis. Better-powered prospective studies are warranted to examine this issue.
A strong association between APS nephropathy and APS-related manifestations such as arterial thromboses and livedo reticularis was found in this series. It is well known that the manifestations of APS are characterized by recurrent episodes (29, 30) in the absence of therapy. Hypothesizing that APS nephropathy may represent an additional feature of APS, we investigated any tendency of the SLE/non-APS patients with APS nephropathy to develop APS manifestations during a mean followup period of 7 years. It was observed that among SLE/non-APS patients with aPL, those with APS nephropathy developed thromboses more frequently than did those without APS nephropathy (P = 0.04). Moreover, patients who had this characteristic renal small-artery vasculopathy developed arterial thromboses, while those without APS nephropathy developed venous thromboses. Previous studies have demonstrated that the arterial thromboses in APS tend to be followed by more arterial thromboses, and that the venous thromboses tend to be followed by more venous thromboses (30–32). Thus, the strong association of APS nephropathy with aPL and the tendency of the patients with APS nephropathy to develop thrombotic events (especially at the same vascular level) suggests that APS nephropathy should be considered as a manifestation of APS, and the role of appropriate anticoagulant treatment (32, 33) should be tested.
In conclusion, APS nephropathy occurred in 39.5% of SLE patients with aPL but in only isolated SLE patients without aPL, suggesting an important role of aPL in the pathogenesis of APS nephropathy. Among SLE patients with aPL, APS nephropathy can be detected in two-thirds of those with APS and in one-third of those without APS, independently of lupus nephritis. Arterial thromboses (especially stroke), pulmonary embolism, livedo reticularis, aCL, and LAC are strongly associated with APS nephropathy. Patients with APS nephropathy develop hypertension, raised serum creatinine levels, and progression of histologic lesions in serial kidney biopsy specimens; these features are associated with a worse renal prognosis. In patients with APS nephropathy, manifestations of APS, especially arterial thromboses, also tend to develop during the course of the disease. Renal pathologists should carefully examine for the presence of APS nephropathy on kidney biopsy specimens obtained from SLE patients with aPL. Clinicians should be aware of this histologic entity in order to propose a rationale for treatment and to maintain close clinical and laboratory followup. We suggest that APS nephropathy should be included in the APS classification criteria, and that the use of anticoagulant therapy should be examined.