Atypical lupus nephritis unmasked after albumin correction: a diagnostic pitfall presenting with cerebral venous sinus thrombosis.

A woman in her 30s presented with generalised swelling and a right occipital-temporal headache. Examination showed grade 4 papilloedema, and magnetic resonance venography revealed thrombosis of the right transverse and sigmoid sinuses extending into the internal jugular vein. Laboratory evaluation demonstrated anaemia, thrombocytopenia, severe hypoalbuminaemia, low complement levels and strongly positive serology for systemic lupus erythematosus (SLE), with a negative antiphospholipid profile. Initial urinary studies showed non-significant proteinuria (<0.5 g/day), making the cause of hypoalbuminaemia uncertain. After albumin infusion, repeat testing revealed borderline nephrotic-range proteinuria (3.044 g/day), and renal biopsy confirmed ISN/RPS (International Society of Nephrology/Renal Pathology Society) class IV diffuse proliferative lupus nephritis. Her thrombosis was attributed to the combined prothrombotic effects of active SLE inflammation, proteinuria and marked hypoalbuminaemia. Treatment with immunosuppression, anticoagulation and supportive care led to clinical improvement. This case highlights the diagnostic challenges of atypical lupus nephritis and emphasises the value of reassessing proteinuria after albumin correction to ensure timely recognition and management.