Physical examination that finds multiple palpable purpuric lesions on the legs of a 7-year-old boy is most suggestive of

Hemorrhages into the skin may produce lesions of varying sizes. Petechiae measure less than 2 mm in size, purpuric lesions measure 2 mm to 1 cm, and ecchymoses are larger than 1 cm. Erythema and telangiectasis do not involve hemorrhage outside of blood vessels. They can be differentiated from true hemorrhages into the skin by the fact that they blanch if direct pressure is applied to them. True purpura may be caused by hemostatic or nonhemostatic defects. Hemostatic defects are caused by platelet or coagulation abnormalities, while nonhemostatic defects generally involve the blood vessels. These vascular abnormalities can be separated into palpable and nonpalpable purpura. The latter may be caused by excess coicosteroids (Cushing's syndrome), vitamin C deficiency (scurvy), infectious agents, or abnormal connective tissue diseases (Ehlers-Danlos syndrome). Causes of palpable purpura include diseases that cause cutaneous vasculitis, such as collagen vascular diseases and Henoch-Schonlein purpura. The latter, also known as anaphylactoid purpura, is a type of hypersensitivity vasculitis found in children. It usually develops 1 to 3 weeks following a streptococcal infection, but it may also occur in relation to allergic food reactions. Cross-reacting IgA or immune complexes are deposited on the endothelium of blood vessels. Patients may develop fever, purpura, abdominal pain, ahralgia, ahritis, and glomerulonephritis. Reference: Robbins & Cotran Pathologic Basis of Disease, 9edition.