Etiology: Often a reaction pattern to internal or external agent; broadly divided into categories: infections, drugs, malignancy, autoimmune connective tissue disease, idiopathic.
History: Symptoms include itching, burning, or pain. Can also be asymptomatic. May have internal involvement and symptoms, e.g., fever, arthritis, abdominal pain, diarrhea, cough, weakness, sinusitis, & hematuria. Physical: Palpable purpura, most commonly over lower legs
(dependent areas). Investigations: Work-up for potential trigger and assessment of systemic involvement, esp. renal; CBC&D, liver enzymes, urinalysis, CRP, Hep B & C, cryoglobulins, ANA, ENA, ANCA, RF, complement; skin biopsy (reveals small vessel vasculitis); immunofluorescence to rule out HSP. DDx:Thrombocytopenia or ITP or TTP, meningococcemia, other vasculitic syndromes.
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