The correct answer is C. It usually occurs after a respiratory tract infection.
This patient has IgA vasculitis, also known as Henoch-Schonlein purpura (HSP). HSP typically occurs after a respiratory tract infection in children.
HSP is much less common in adults. A DIF biopsy showing perivascular IgA deposition is diagnostic (C3 and fibrin may also deposit perivascularly). Two percent of patients develop permanent renal impairment. Treatment is mainly supportive as HSP is typically self-limited. Corticosteroids may be effective in rapid resolution of renal manifestations and treating joint and abdominal pain, but they are not proven effective for treating organ manifestations and complications, such as glomerulonephritis, bowel infarction or intussusception. Mycophenolate mofetil or cyclosporine A may be better treatment choices in case of renal involvement. Other immunosuppressive and immunomodulating drugs, such as rituximab and dapsone, are promising, but larger studies are needed to confirm these findings. Cancer screening should be considered in older males diagnosed with Henoch-Schönlein purpura.
References: PMID: 28654132