Isolated Antiphospholipid Syndrome Nephropathy (<scp>aPL</scp> Nephropathy)—A Rare Cause of a Rapid Decline in Kidney Function in a Patient With Systemic Lupus Erhythematosus

Lupus nephritis (LN) is one of the most common renal manifestations of systemic lupus erythematosus (SLE). However, conditions other than LN can result in a rapid decline in kidney function. We present a clinical case of a young patient with SLE who developed arterial hypertension, arthralgia and morning stiffness in knee and hand joints, an increase in serum creatinine levels from 194 to 532 mol/L, proteinuria of 1.65 g/L and thrombocytopenia of 1000/μL. Kidney biopsy showed isolated antiphospholipid antibody nephropathy (aPL-N) without any signs of proliferative LN or tubulointerstitial nephritis. The patient was treated with low-molecular-weight heparin, followed by warfarin (target INR 2.0-3.0), low-dose glucocorticoids and azathioprine, resulting in SLE remission and partial recovery of kidney function. This study demonstrates that isolated aPL-N can cause a rapid decline in kidney function in patients with SLE. To avoid diagnostic errors, kidney biopsy should be performed in a timely manner in all patients with SLE according to standard indications.