IgA Vasculitis (Henoch–Schönlein Purpura)
The histopathologic features of IgA Vasculitis are leukocytoclastic vasculitis or necrotizing small-vessel vasculitis. The characteristic direct immunofluorescence finding is predominantly IgA deposition in affected blood vessels. IgA can also be found in the glomerular mesangium. The skin biopsy finding of IgA deposition is what makes this syndrome pathologically different from other forms of small-vessel vasculitis. Many cases of IgAV occur following a respiratory infection, for which IgA is important for mucosal immunity.
The classic tetrad of palpable purpura, arthritis, abdominal pain, and renal disease occurs in up to 80% of cases. The rash may begin as macular erythema and urticarial lesions, but may progress rapidly to purpura. The lower extremities and buttocks are the most common sites for the rash. The joints are involved in 60% to 84% of patients. The involvement is symmetrical and most commonly involves the ankles and knees. GI lesions may cause severe cramping, abdominal pain, intussusception and hemorrhage. Renal involvement is seen in 50% of patients and is usually manifest as asymptomatic proteinuria and hematuria.
IgAV is often acute in onset, and resolution is rapid and complete in 97% of cases, except in a minority of patients with chronic renal disease. Persons of any age can be affected, but IgAV occurs primarily in children between the ages of 2 and 10 years. Adults have more severe disease with a higher frequency of renal involvement. Patients of any age (especially adults) suspected of having IgAV for whom a skin biopsy is negative for IgA should be evaluated for ANCA-associated vasculitis, anti-C1q disease, or IgA paraproteinemia.
The disease is generally self-limited, lasting from 6 to 16 weeks. For mild cases, supportive treatment alone may be adequate. Arthritis responds to nonsteroidal antiinflammatory drugs (NSAIDs). Systemic glucocorticoids may be used in patients with GI involvement or bleeding. Progressive renal disease is difficult to treat and usually does not respond to glucocorticoids. Aggressive treatment with high-dose glucocorticoid pulses and cytotoxics should be considered in patients with poor prognostic factors of proteinuria >1 g/day, nephrotic syndrome, and crescentic glomerulonephritis >50% crescents.