Which histologic findings are characteristic of Henoch-Schönlein purpura (IgA vasculitis)?

Updated: Oct 28, 2020
  • Author: Rajendra Bhimma, MBChB, MD, PhD, DCH (SA), FCP(Paeds)(SA), MMed(Natal); Chief Editor: Craig B Langman, MD  more...
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Answer

Histopathologic features of the skin lesions in infantile IgAV can range from a typical leukocytoclastic vasculitis with or without fibrinoid necrosis to the less specific findings of a lymphohistiocytic perivascular infiltrate with extravasation of erythrocytes.

Direct immunofluorescence (DIF) testing is a useful adjunct to histopathology; the yield is substantially higher when the test is performed within 48 hours of presentation. Immunofluorescence studies reveal perivascular IgA deposition in almost all patients; this finding is rare in infantile IgAV, in which C3 and IgM are most commonly found in the affected vessel walls.

IgAV often involves the kidneys. Kidney histology in IgAV varies considerably. In some cases, most glomeruli appear unaffected on light microscopy; only a few show mesangial proliferation. In instances of moderate kidney involvement, focal and segmental intracapillary and extracapillary proliferation may be present with adhesions and small crescents. Severe cases are characterized by a diffuse proliferation with infiltration of neutrophils and circumferential crescents in most of the glomeruli. Tubular atrophy and interstitial infiltration with mononuclear cells may also be present.

In most patients, IgA deposits in the mesangium and the walls of cutaneous capillaries are detected. The IgA deposited in the mesangium is mainly of the IgA1 subclass, though IgA2 deposits are noted in rare cases. In addition to IgA, the deposits in mesangium and cutaneous capillaries frequently contain C3, IgG, and fibrin. C3 deposits are often accompanied by properdin, whereas C1Q and C4 are usually not present. This observation suggests that the complement components have been activated by means of the alternative pathway.


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