Snapshot A 56-year-old woman presents to her dermatologist’s office for a rash on both of her shins. She reports that this rash started a day ago and that her legs ache also. She has had low-grade fevers and some recent weight loss. Her past medical history includes diabetes, hypertension, and systemic lupus erythematosus, which was diagnosed a year ago but has not had a flare in over 6 months. On physical exam, she has bilateral symmetric non-blanching palpable purpura. Several lesions on her right shin have coalesced into violaceous plaques. She is started on steroids. Introduction Clinical definition login to view 2 more bullets Epidemiology Incidence login to view 1 more bullet Demographics login to view 1 more bullet Location login to view 1 more bullet Etiology Idiopathic (50% of cases) Autoimmune disease (15-20% of cases) Drugs (i.e., levamisole-tainted cocaine) Infections (i.e., group A streptococcus, hepatitis B, or hepatitis C) Malignancy Pathogenesis login to view 3 more bullets Associated conditions login to view 2 more bullets Presentation Symptoms login to view 10 more bullets Physical exam login to view 4 more bullets Studies Labs login to view 1 more bullet Skin biopsy of fresh lesions (24-48 hours old) login to view 8 more bullets Differential Polyarteritis nodosa login to view 2 more bullets DIAGNOSIS Making the diagnosis login to view 1 more bullet Treatment Medical login to view 9 more bullets Complications Involvement of internal organs Prognosis Recurrence occurs in up to 10% of patients