Background: Immunofluorescence (IF) in PGNMID most commonly demonstrates a granular texture of deposits along the glomerular capillary wall (GCW). Less frequently, semi-linear and smudgy appearances have also been reported. Here, we report a novel case of PGNMID with strong linear staining of the GCW with IgG kappa.

Case Report: 51-year-old male presented with a three-day history of dyspnoea, orthopnoea and oliguria. He had a 20 pack-year smoking history. He was hypertensive 206/104 mmHg and clinically volume overloaded. Biochemistry showed a serum creatinine of 504 umol/L, albumin of 29 g/L, urine protein-creatinine-ratio (U-PCR) of 557 g/mol with microscopic haematuria. Glomerulonephritis screen including anti-GBM was negative. A low C3 was noted—0.39 g/L [0.90–1.80] and normal C4. Worsening biochemistry and refractory fluid overload rendered the patient to haemodialysis. Light microscopy demonstrated diffuse endocapillary and mesangial hypercellularity, and <10% interstitial fibrosis. Immunofluorescence demonstrated heavy linear IgG and kappa deposition along the GCW, and granular deposition in the mesangium, with sparing of the tubular basement membrane. IF for lambda was negative. Electron microscopy showed amorphous deposits within the mesangium and subendothelial regions, with severe foot process effacement. Serum protein electrophoresis, serum free light chain ratio, flow cytometry on peripheral blood, and a bone marrow aspirate and trephine failed to identify a plasma cell clone. He was treated with 2 × 750 mg doses of rituximab 2 weeks apart, in addition to a weaning course of oral prednisolone. One month later, the patient became independent of dialysis.

Conclusions: This unique case shows that PGNMID can also present with a strong linear pattern. Notably, his anti-GBM serology and tests for diabetes were negative. Early recognition and treatment may confer a favourable response.