Nephrotic Syndrome Secondary to Rheumatoid Arthritis in a Known Case of Dilated Cardiomyopathy: A Diagnostic Insight

Rheumatoid Arthritis (RA) is a chronic systemic autoimmune disease that primarily affects joints but can lead to extra-articular complications, including renal and cardiac involvement, which can significantly impact patient prognosis. This case report describes a 44-year-old woman with a 15-year history of poorly controlled RA, characterised by multiple rheumatic nodules and inconsistent treatment adherence. She was diagnosed with Dilated Cardiomyopathy (DCMP) one year prior, with an ejection fraction of 20%, and presented with progressive bilateral pedal oedema and dyspnoea. Clinical examination revealed hepatomegaly and multiple joint nodules. Laboratory investigations showed hypoalbuminaemia, severe dyslipidaemia, and nephrotic-range proteinuria. Renal biopsy, including light microscopy, immunofluorescence, and electron microscopy, confirmed stage I membranous nephropathy secondary to RA, with negative PLA2R staining indicating a secondary aetiology rather than primary membranous nephropathy. The co-existence of DCMP and membranous nephropathy posed diagnostic and management challenges, as symptoms overlapped between cardiac and renal dysfunction. This rare combination highlights the need for comprehensive evaluation in patients with longstanding autoimmune diseases to identify uncommon renal manifestations early. Reporting this case underscores the importance of multidisciplinary care in complex comorbidities and the potential benefits of screening RA patients for renal involvement, particularly those with poor disease control, to improve outcomes and prevent progression.