Renal involvement in the anti-phospholipid syndrome

Abstract

1. In utilizing the consensus criteria for classification of APS, it is important to note the following key points:◆ the criteria are intended primarily for classification of patients entered into clinical studies rather than as clinical diagnostic criteria for APS;◆ the diagnosis of APS requires that a patient with APS manifest at least one of two clinical criteria (vascular thrombosis or pregnancy morbidity) and laboratory detection of aPL (i.e. LAC, aCL, and/or anti-β‎2GPI;◆ the criteria recommend documentation of the co-existence of SLE or other diseases, as well as the co-existence of specific risk factors for vascular thrombosis, rather than distinguishing specific categories of APS.2. In general, LAC are considered the most specific predictor of APS, anti-β‎2GPI are of intermediate specificity, and aCL are the least specific. Multiple aPL tests should be used, as patients may be positive in one test and negative in another.3. As macrovascular thrombosis in APS can occur in either the arterial or the venous bed, it is important to monitor secondary risk factors that are specific to these beds, including stasis, vascular injury, medications such as oral contraceptives, and established risk factors for atherosclerotic disease.4. Venous thrombosis, in particular deep venous thrombosis of the lower extremities, is the most common manifestation of APS, with up to 50% of APS patients suffering pulmonary emboli.5. Arterial thromboses are less common than venous thromboses in APS, and most events show features consistent with ischaemia or infarction.6. Renal lesions attributable to APS do not differ significantly in patients with and without concomitant SLE, and are best understood from a pathophysiological perspective, with emphasis on two features: 1) the nature and size of the involved vessels, and 2) the acuteness versus chronicity of the thrombotic process.7. Renal arterial involvement in APS generally consists of occlusive lesions resulting from either in situ thrombosis or embolism from an upstream source. These lesions are commonly asymptomatic and detected incidentally.8. Renal vein thrombosis occurs more frequently in APS patients with SLE (∼10%) than in patients without SLE (≤1%), most likely because of SLE-associated proteinuria and nephrotic syndrome.9. The most important renal manifestation of APS is TMA, which can vary widely in presentation, from an explosive AKI requiring dialysis to a mild progressive CKD. TMA may be present in ≥50% of primary APS patients with renal findings of any sort, including hypertension, microscopic haematuria, and/or minimal levels of proteinuria.10. The renal histopathological features of APS reflect a combination of two major pathophysiological processes: 1) TMA (acute or chronic); and 2) ischaemia secondary to upstream arterial and/or arteriolar lesions.11. A minority (<1%) of APS patients presents with ‘catastrophic APS’, characterized by multiple simultaneous organ involvement and failure, often resulting in death. Large vessel thrombosis is less common in patients with catastrophic APS, who tend to present with an acute TMA affecting the microvasculature of multiple organs.12. The most important risk factor for thrombosis in APS, and the only one sufficiently predictive to warrant treatment, is a previous history of thrombosis.13. The literature does not support the effectiveness of aspirin for primary prophylaxis of thrombosis in aPL-positive patients. On balance, however, given the minimal risk associated with low-dose aspirin, it seems reasonable to recommend its usage in aPL-positive individuals, in accord with traditional guidelines for the prevention of cardiovascular disease.14. Although controlled studies are lacking, hydroxychloroquine may be protective as a primary prophylactic agent against the development of thrombosis in aPL-positive patients, especially in the setting of SLE.15. A major role in prophylaxis should also be given to elimination of non-aPL-associated risk factors for thrombosis, as well as to modification of secondary risk factors for atherosclerosis.16. A beneficial role for anticoagulation in decreasing the rate of recurrence of thrombosis has been shown. In two prospective randomized controlled trials of warfarin, intermediate-intensity treatment (INR, 2.0–3.0) was as effective as high-intensity treatment (INR, 3.0–4.0). Some authorities, however, recommend high-intensity warfarin for APS patients with an arterial thrombosis and/or multiple thrombotic events, as a majority of patients in both studies had venous events, and patients with recurrent thromboses were excluded.17. The use of statins, and probably ACEI, seems justified for both primary and secondary prophylaxis in APS, given the favourable therapeutic profile of these agents, their potentially beneficial anti-inflammatory and anti-thrombotic effects, and the high prevalence of renal disease among APS patients.