Background: Adult-onset Henoch-Schönlein purpura nephritis (HSPN) and primary IgA (IgAN) nephropathy have been considered indistinguishable immunohistopathologically and are often considered as two extremes of one disease entity. We postulate that adult-onset Henoch-Schönlein can be distinguished histologically from primary IgAN and that both diseases differ in their immunopathological mechanisms.
Methods: Twenty consecutive patients with adult-onset HSPN were studied. Serum was analysed for circulating IgA immune complexes; renal biopsies were analysed by light and electron microscopy (EM). As disease controls, 40 IgAN patients were studied.
Results: Intracapillary leukocyte margination was seen in 15 of the 20 patients and cellular crescent formation in all renal biopsies of the HSPN patients. IgAN biopsies showed a few small crescents without intracapillary leukocytes. In 16 HSPN patients, EM was performed and in 10, no dense deposits were found. In all biopsies of IgAN patients, typical 'humps' were found. In 6 of 9 analysed HSPN patients, intermediate to large circulating immune complexes were found, whereas in 4 of 28 analysed patients with primary IgAN small circulating immune complexes were found.
Conclusions: We consider adult-onset HSPN distinguishable in histology and ultrastructure from primary IgAN. We believe adult-onset Henoch-Schönlein to be a circulating immune complex disease.