8-year-old boy • palpable purpura on the legs with arthralgia • absence of coagulopathy • upper respiratory infection • Dx?

HSP vasculitis causes abdominal pain in 50% to 75% of patients due to proximal small-bowel submucosal hemorrhage and bowel wall edema.³ In children with HSP, 20% to 55% have been shown to develop renal disease,⁴ which can range in severity from microscopic hematuria to nephrotic syndrome.³ To ensure prompt treatment of renal manifestations, renal function should be monitored regularly via blood pressure and urinalysis during the course of HSP and after resolution. Renal disease associated with HSP can be acute or chronic.

This case was different because our patient did not exhibit all elements of the classic tetrad of HSP, which includes the characteristic rash, abdominal pain, renal involvement, and arthralgia.

Incidence. HSP is more common in children than adults, with average annual incidence rates of 20/100,000 and 70/100,000 in children in the United States and Asia, respectively.⁵ While 90% of HSP cases occur in children < 10 years, the peak incidence is at 6 years of age.⁶ Complications from HSP are more common in adults than in children.⁷ Caucasian and Asian populations have a 3- to 4-times higher prevalence of HSP than black populations. The male-to-female ratio is 2 to 1.⁶

The diagnosis of HSP is usually made clinically, based on the distinctive rash, which typically is symmetrical, involving the buttocks, lower legs, elbows, and/or knees. HSP also can be confirmed via skin biopsy and/or direct immunofluorescence, which can identify the presence of IgA in the vessel walls.

The presence of 3 or more of the following criteria also suggests HSP: palpable purpura, bowel angina, gastrointestinal (GI) bleeding, hematuria, ≤ 20 years of age at onset, and no medications prior to presentation of symptoms (87% of cases correctly classified). Fewer than 3 of these factors favor hypersensitivity vasculitis (74% of cases correctly classified).⁸

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