Diagnosis: Henoch-Schönlein purpura
This patient has Henoch-Schönlein purpura (HSP), a systemic vasculitis, secondary to hypersensitivity, occurring most commonly in children and young adults. Its classic triad includes palpable purpura, abdominal pain or renal involvement, and arthritis.1
Purpura is typically nonblanching, as it represents extravasation of blood into skin, 2 but lesions may also include urticarial wheals or occasional target lesions. As seen in this patient, the lower extremities and buttocks are typically affected. This rash is pressure- and gravity-dependent and pressure lines may develop, causing “sock lines” such as those seen on this young woman’s calves.1,2 Arthritis also tends to affect large joints in lower extremities more severely than upper extremities, and ankles and knees may be swollen and tender, as observed in our patient.
Abdominal pain, not present in this case, develops in up to 65% of cases, and may be accompanied by vomiting, hematemesis, or blood in stools.
Renal involvement is by far the most long-reaching and potentially serious complication of HSP, particularly in adults. Although only 1% of all HSP patients may develop end-stage renal failure, it is estimated that in adults, this number may be as high as 11%.3,4 The young woman in question presented with microscopic hematuria initially, which had resolved by the time of her next visit, 4 days later. A worse prognosis is associated with those patients who exhibit both nephritic and nephrotic features, with hematuria and proteinuria, where clinical remission has been shown to present only in 20% of these patients. Finally, as renal involvement may develop up to years after initial diagnosis, follow-up is crucial to monitor renal function.4
Cause is unknown
The cause of HSP is unknown, although it is thought to be secondary to deposition of immune complexes, and has been associated with vaccinations, viral infections, allergens in foods, drug reactions, exposure to cold, and bacterial respiratory infections, particularly involving group A streptococci.1,2 This patient had been diagnosed with streptococcal pharyngitis and had been given a course of clindamycin due to her numerous drug allergies. Although the precise cause of her HSP is not definite, drugs have been shown to cause approximately 10% of acute cutaneous vasculitis cases, and she had never before been given clindamycin, possibly pointing to the origin of her disease.5