How is HSP diagnosed
How is the diagnosis confirmed? What role does IgA play in the pathogenesis?
A skin biopsy with immunofluorescence showing a leukocytoclastic vasculitis with predominantly IgA vessel wall deposition in the appropriate clinical setting is diagnostic of HSP, but HSP is typically a clinical diagnosis. Notably, HSP has been reported most often to occur following an upper respiratory tract infection. It also can occur before or during the course of ANCA-associated vasculitis or Crohn disease. Each of these triggers involves inflammation at mucosal surfaces where IgA plays a role in mucosal immunity. In patients with HSP, serum IgA1 has been shown to be galactose-deficient at the hinge region O-linked glycan causing it to form aggregates that interact with IgG forming IgA–IgG immune complexes that deposit in tissues. IgA anticardiolipin antibodies may also be involved in the pathogenesis.