A case of fibrillary glomerulonephritis with unusual IgM deposits and hypocomplementemia

Fibrillary glomerulonephritis (FGN) is rare immune-mediated GN with predominant immunoglobulin (Ig) G deposits, normal serum complement levels, and poor prognosis. The incidence of FGN is less than 1% in the adult population, and only six pediatric cases have been reported in the English literature. A 12-year-old girl presented with acute nephrotic–nephritic syndrome mimicking atypical clinical features of acute poststreptococcal GN (APSGN). Clinical features had completely resolved in 2 weeks, but the serum complement levels remained low. Renal biopsy was done 6 months later, and she was diagnosed as having FGN with unusual IgM deposits. Despite persistently low serum complement levels during the subsequent 3 years, clinical relapse did not develop. This case was an atypical form of FGN characterized by unusual IgM deposits, persistent hypocomplementemia, and good prognosis, which suggests that childhood FGN is not necessarily a disease with poor prognosis.