Idiopathic inflammatory myopathy and C3 glomerulopathy: a rare association

Idiopathic inflammatory myopathies represent a spectrum of autoimmune disorders primarily characterized by muscle inflammation. While renal involvement in idiopathic inflammatory myopathies has historically been considered rare, recent findings indicate a prevalence of approximately 21–23%. Renal manifestations in idiopathic inflammatory myopathies are generally secondary to acute renal injury from rhabdomyolysis or, more rarely, occur through autoimmune mechanisms leading to glomerulonephritis. Here, we present the case of a 21-year-old male diagnosed with idiopathic inflammatory myopathy positive for anti-Jo antibodies and concurrent C3 glomerulonephritis, which improved following Rituximab therapy. The description of this case provides insights for future research into the role of alternative complement pathway dysregulation in idiopathic inflammatory myopathy-associated C3 glomerulopathy.