The sine qua non of IgA vasculitis (formerly Henoch-Schönlein purpura) is nonthrombocytopenic purpura, caused by inflammation in blood vessels of the superficial dermis.
The pathologic hallmarks of IgA vasculitis are a leukocytoclastic vasculitis and deposition of immunoglobulin (Ig) A in the walls of involved blood vessels.
The tetrad of purpura, arthritis, glomerulonephritis, and abdominal pain is often observed. However, all four elements are not required for the diagnosis.
More than 90% of cases occur in children. The disease is self-limited most of the time, resolving within a few weeks. Adult cases are sometimes more recalcitrant.
Renal insufficiency develops in less than 5% of patients with IgA vasculitis. The long-term renal prognosis depends mainly on the degree of initial damage to the kidney.
IgA vasculitis can be mimicked by other forms of systemic vasculitis that are more often life-threatening. For example, antineutrophil cytoplasmic antibody (ANCA)–associated vasculitides such as granulomatosis with polyangiitis and microscopic polyangiitis may also present with purpura, arthritis, and renal inflammation. Both of these disorders have the potential for serious involvement of other organs (eg, the lungs and peripheral nerves) and carry more dire renal prognoses.
IgA vasculitis (formerly Henoch-Schönlein purpura) is the most common form of systemic vasculitis in children, with an annual incidence of 140 cases per million persons. The peak incidence is in the first and second decades of life (90% of patients are younger than 10 years of age), with a male to female ratio of 2:1. The incidence is significantly lower in adults, with a mean age at presentation of 50 years. Males and females are affected equally and although IgA vasculitis affects all ethnic groups, it is reportedly less common among blacks. Some epidemiologic studies suggest that IgA vasculitis is more prevalent in the winter months.
IgA vasculitis may be misdiagnosed as another form of vasculitis—most commonly hypersensitivity vasculitis (see Chapter 33)—because of the frequent failure to perform direct immunofluorescence testing on skin biopsy specimens. In two-thirds of the cases, the disease follows an upper respiratory tract infection, with onset an average of 10 days after the start of respiratory symptoms. Despite this association, no single microorganism or environmental exposure has been confirmed as an important cause of IgA vasculitis. IgA vasculitis can also be induced by medications, particularly antibiotics. The American College of Rheumatology 1990 criteria for the classification of IgA vasculitis are shown in Table 35–1. The first Chapel Hill Consensus Conference on the nomenclature of vasculitides defined IgA vasculitis as a form of vasculitis characterized by the following: (1) IgA-dominant immune deposits within vessel walls; (2) small-vessel involvement (ie, capillaries, venules, or arterioles); and (3) skin, gut, renal, and joint manifestation.
Table 35–1.The American College of Rheumatology 1990 Criteriaa for the classification of IgA vasculitis.