C1q-Associated Nephropathy in a Patient with Prior Acute Interstitial Nephritis and Treated Hepatitis C Infection

Abstract

C1q nephropathy (C1qN) is an uncommon glomerular disorder defined by dominant mesangial deposition of complement component C1q on immunofluorescence in the absence of clinical or serological evidence of systemic lupus erythematosus (SLE). It classically presents with nephrotic syndrome and shows variable light microscopic appearances that may mimic minimal change disease (MCD) or focal segmental glomerulosclerosis (FSGS). We report a 48-year-old male farmer with a history of biopsy-proven acute interstitial nephritis (AIN) and previously treated hepatitis C virus (HCV) infection who presented with nephrotic-range proteinuria, severe hypoalbuminemia, and marked dyslipidemia. Renal biopsy demonstrated dominant mesangial C1q positivity with trace IgG, C3, and light chains, while electron microscopy revealed electron-dense deposits confined exclusively to the mesangium. The patient was started on high-dose corticosteroids (prednisolone 1 mg/kg/day) as per KDIGO adult nephrotic syndrome recommendations, achieved complete remission by four weeks, and is currently maintained on a six-month tapering schedule. This case highlights the importance of differentiating C1qN from mimics and suggests a potential link between antecedent immune insults and mesangial immune complex disease.