When Atypical Becomes Typical: A Fulminant Seronegative Anti-GBM Disease.

Anti-glomerular basement membrane (GBM) disease is a rare autoimmune disorder characterized by circulating anti-GBM antibodies, rapidly progressive glomerulonephritis, and linear immunoglobulin G (IgG) deposition along the GBM. In contrast, atypical anti-GBM disease presents with an indolent course, absence of detectable antibodies, and variable histologic features. We report a 24-year-old male who presented with severe kidney failure (serum creatinine 17 mg/dL) and no pulmonary symptoms. Serologic tests for anti-GBM, ANCA, and ANA were negative, and complement levels were normal. Kidney biopsy revealed crescentic glomerulonephritis with 55% cellular crescents and linear polytypic IgG and C3 staining along the GBM. The patient was treated with hemodialysis, high-dose corticosteroids, cyclophosphamide, and plasma exchange according to standard anti-GBM protocols. Antibody titers remained undetectable throughout therapy. Despite aggressive treatment, kidney function did not recover, leaving the patient dialysis-dependent. This case represents an atypical manifestation of atypical anti-GBM disease, mimicking the severe phenotype of the classic form but lacking serologic confirmation. It highlights the diagnostic uncertainty and therapeutic challenges in seronegative presentations, in which antibody titers cannot guide treatment or transplantation decisions. Such cases may be more accurately described as crescentic glomerulonephritis with linear IgG staining, reflecting their overlap with classic anti-GBM disease.