Kidney involvement in antiphospholipid syndrome – current diagnostic and management problems

Antiphospholipid syndrome (APS) is currently considered a systemic autoimmune disease with coexisting recurrent venous or arterial thrombosis, obstetric complications, and the presence of antiphospholipid antibodies (aPL). The marker antibodies for APS are: anticardiolipin antibodies, anti-b2-glikoprotein I antibodies, and lupus anticoagulant (LAC) [1]. APS, which was defined for the first time in 1985, has been diagnosed more and more frequently and is better and better treated. The classification criteria of the disease defined in 2006 include: the presence of venous or arterial thrombosis of any organ, determined obstetric complications, and detection in at least two tests (at least 12 weeks apart) of the marker antiphospholipid antibodies [1]. APS can be isolated (primary APS) in the absence of other autoimmune diseases or (as secondary APS) associated with a number of autoimmune diseases, mostly with systemic lupus erythematosus (SLE). Many clinical faces of APS may be observed: • APS with vascular events, • APS with pregnancy morbidity (OAPS), • catastrophic antiphospholipid syndrome (CAPS), • asymptomatic antiphospholipid antibodies, • APS with non-classification criteria manifestations, like: livedo reticularis, thrombocytopaenia, valvular heart disease, cognitive disorders, APS nephropathy (APSN). It is recommended that the aforementioned symptoms be included in the classification criteria of APS [1–3]. The classification criteria of the disease defined in 2006 do not include renal involvement, frequently occurring in APS, and mentioned already in the first descriptions of this syndrome [1]. APS causes various pathophysiological effects concerning the kidneys. The renal manifestations of APS may result from thrombosis occurring at any location within the renal vasculature. The renal involvement is associated with both primary and secondary APS [4–10]. There are clinical observations and data from literature showing that kidney involvement is frequently found in APS. There is, however, no clear connection between the presence of a significant level of aPL and advancing of nephropathy, especially occurring in the course of particular connective tissue diseases [8, 11, 12]. The clinical syndromes of renal involvement in APS include [4–10]: • renal artery stenosis, • renal vein thrombosis, • arterial hypertension (from modest to severe), • antiphospholipid associated nephropathy (APSN) – small vessel vaso-occlusive lesions (acute and chronic), • chronic kidney disease at all stages, • allograft vascular thrombosis. Large-vessel thrombosis (renal artery stenosis, renal vein thrombosis) represents a well-defined manifestation of APS and can be used for diagnosis of APS. Renal arterial thrombosis is associated with worsening of hypertension, renal infarction with loin pain, and acute or chronic renal failure. Renal vein thrombosis may be presented as proteinuria, decreasing of glomerular filtration rate (GFR), loin pain, haematuria, or secondary pulmonary thrombosis. APSN, acute or chronic, with variable degrees of severity, and with nephritic or nephrotic syndrome, may be presented in kidney biopsy specimens as thrombotic microangiopathy (TMA), fibrous intimal hyperplasia (FIH), or focal cortical atrophy (FCA) [7, 8, 12]. Recently a new subset of the APS has been proposed: microangiopathic antiphospholipid syndrome (MAPS) comprising those patients presenting thrombotic microangiopathy and antiphospholipid antibodies [5–7]. TMA can be one of the manifestations of the APS and may affect vessels in different organs, resulting in ischaemia and organ failure. The clinical picture depends on the size and type of vessel affected and the organ involved. When capillaries, arterioles, or venules are affected, histopathological characteristics are virtually identical to those of TMA resulting from other caus-