Snapshot A 5-year-old boy presents to the emergency room for abdominal pain and rash on his legs. He also reports having intermittent joint pains. A few weeks ago, he had an upper respiratory infection. On physical exam, he has nontender palpable purpura on his buttocks and lower extremities. His abdomen is mildly tender. Urine studies show proteinuria and hematuria. (Henoch-Schonlein purpura/IgA vasculitis) Introduction Clinical definition vasculitis caused by immune complex deposition Pathogenesis circulating antigens induce antibody formation the antibodies then bind to antigens, creating immune complexes the immune complexes then deposit in small vessels, activating complement and causing a vasculitis General clinical features palpable dark-red or purple purpura may itch, burn, or be nontender may ulcerate Studies most cases are diagnosed clinically, but a biopsy may be needed direct immunofluorescence deposition of C3, IgM, IgA, and/or IgG Cryoglobulinemic Vasculitis Clinical definition small-vessel vasculitis caused by mixed cryoglobulins affecting the skin, peripheral nervous system, and kidneys associated with hepatitis C virus (HCV) infection occurs in adults Presentation peripheral neuropathy skin involvement palpable purpura ulcerations livedo reticularis joint pain renal involvement membranoproliferative glomerulonephritis no gastrointestinal symptoms (in contrast to Henoch-Schonlein purpura) Studies cryoglobulins isolated from the serum urine studies proteinuria hematuria Treatment treat underlying HCV infection corticosteroids Henoch-Schonlein purpura (IgA Vasculitis) Clinical definition IgA-mediated small vessel vasculitis that often follows an upper respiratory infection especially with group A streptococcus or parvovirus B19 occurs in children Presentation triad of nontender palpable purpura on buttocks and lower extremities may ulcerate arthralgias colicky abdominal pain constitutional symptoms hematuria Studies urine studies proteinuria hematuria direct immunofluorescence IgA deposition in small vessels on direct immunofluorescence histology IgA deposition in small vessels on staining leukocytoclasis Treatment typically resolves spontaneously over time angiotensin-converting enzyme (ACE) inhibitor indication for persistent proteinuria, which may result in end-stage renal disease or glomerulonephritis