PRESENTATION AND DIAGNOSIS

The major features include palpable, nonblanching purpura (often on the lower extremities), nonerosive oligoarthritis, renal disease, and gastrointestinal disease. Most patients, however, do not exhibit all four of these components.

The renal disease can include microscopic or macroscopic hematuria, proteinuria, renal insufficiency, or a combination. Especially in adults, the proteinuria may be severe enough to cause signs and symptoms of the nephrotic syndrome, and acute kidney injury may also occur. The gastrointestinal disease, which occurs secondary to submucosal edema and hemorrhage, may be limited to pain and vomiting. Some patients, however, may experience more significant complications, such as frank gastrointestinal hemorrhage or intussusception. Less common systemic manifestations include scrotal pain or swelling, as well as central nervous system disease (i.e., headache, seizures).

The major presenting symptoms tend to be palpable purpura and arthritis, with gastrointestinal and renal involvement developing in some patients over subsequent days and weeks. This sequence, however, is not universal; in 20% to 40% of patients, for example, gastrointestinal symptoms may precede the rash. Likewise, 20% to 50% may have renal involvement at the initial presentation. Urinalysis may be remarkable for dysmorphic red blood cells, red blood cell casts, and protein. Laboratory analysis of serum is generally unremarkable, although some patients may have evidence of mild renal dysfunction. In addition, those with more severe proteinuria may be found to have hypoalbuminemia and hypercholesterolemia as parts of the nephrotic syndrome. Complement levels are generally normal. Frank gastrointestinal bleeding may cause anemia, which should be assessed using guaiac testing of stool. Platelet counts and assays of clotting function should be normal, which can be used to exclude other causes of purpura. IgA levels are elevated in about half of patients but are neither sensitive nor specific for the diagnosis of HSP.

According to current diagnostic criteria, a patient is considered to have HSP if purpura or petechiae have a lower limb predominance, there is no evidence of thrombocytopenia or coagulopathy, and any one of following four criteria are met: (1) abdominal pain; (2) arthritis or arthralgia; (3) renal involvement (hematuria, proteinuria); and (4) histopathology showing IgA dominant or codominant deposition. The diagnosis can usually be established based on clinical indicators. When the diagnosis is uncertain but the level of suspicion is high, a skin biopsy may be performed, which classically reveals a leukocytoclastic vasculitis with IgAdominant deposition seen on immunofluorescence.