A Rare Convergence: Suspected Secondary IgA Nephropathy Associated with Dermatomyositis

Introduction: IgA nephropathy (IgAN) is characterized by the accumulation of circulating immune complexes of immunoglobulins and galactose-deficient IgA antibodies in the glomeruli, leading to inflammation and tissue injury. Dermatomyositis, an autoimmune disorder affecting skin and muscles, is rarely linked to kidney manifestations. We present a patient with dermatomyositis who developed sub-nephrotic range proteinuria and microscopic hematuria and was found to have secondary IgAN while on immunosuppressive therapy. Case Description: A 58-year-old White man with a known history of hypertension, dermatomyositis on Methotrexate 17.5 mg weekly, Tocilizumab 162 mg once a week, and erosive arthritis, presented for evaluation of sub-nephrotic range proteinuria (UPRC 2.5 g/g) with normal kidney function. Initial workup, including ultrasound, complements C3 and C4, and serologic workup for autoimmune disease and chronic infection was negative. Fat pad biopsy was negative for amyloid. Kidney biopsy showed IgAN with the presence of tubuloreticular inclusions on electron microscopy, suggesting a secondary autoimmune nature. He was started on Dapagliflozin, Olmesartan, and Spironolactone with a marked reduction in proteinuria. Discussion: This case highlights the rare occurrence of secondary IgAN in a patient with dermatomyositis under immunosuppressive therapy. IgAN has been associated with other autoimmune diseases, such as inflammatory bowel disease, celiac disease, and Sjogren’s syndrome, but is rarely associated with idiopathic inflammatory myopathies, such as dermatomyositis. Our findings contribute insights into the diverse clinical presentations of idiopathic inflammatory myopathy-associated complications and highlight the need for further studies to evaluate the relationship between idiopathic inflammatory myopathies, such as dermatomyositis, and IgAN.