Resolution of clinical and pathologic features of C1q nephropathy after rituximab therapy

C1q nephropathy is a rare idiopathic glomerulopathy characterized by mesangial deposition of immunoglobulin and complement with C1q dominance or co-dominance, and the absence of clinical and laboratory evidence of systemic lupus erythematosus. Its clinical course is unpredictable and the response to corticosteroid or cytotoxic treatment is variable. Here, we report two cases of C1q nephropathy, one in a child and one in an adult, both presenting with impaired renal function and massive proteinuria. Both patients failed to respond to immunosuppressive medications; however, rituximab, an anti-CD20 antibody, was effective in preserving renal function in one patient and eliminating the need for hemodialysis in the other. In one patient, histologic regression of abnormalities was documented over 3 years post-treatment. Both patients have remained off other immunosuppressive medication for a prolonged period with stable renal function. These cases are, to our knowledge, the first reported successful treatment of C1q nephropathy with rituximab.