IgM in lesional skin of adults with Henoch-Schönlein purpura is an indication of renal involvement.

BACKGROUND: Henoch-Schönlein purpura (HSP) is a multisystem disease believed to be a consequence of the entrapment of circulating IgA-containing immune complexes in blood vessel walls throughout the skin, kidneys, and gastrointestinal tract. The skin manifestations are characterized by nonthrombocytopenic palpable purpura over the lower extremities.

OBJECTIVE: We assessed adult patients with HSP who had nonthrombocytopenic palpable purpura on the extensor surfaces of their lower limbs, and had no associated connective tissue disease. Patient medical records, including clinical presentation, laboratory data, and direct immunofluorescence (DIF) reports, were reviewed retrospectively.

METHODS: We reviewed the records of 25 adult patients with HSP who presented at our department, between 2006 and 2008, with an initial cutaneous manifestation of palpable purpura on their lower extremities. Adult HSP was defined in all cases as documented leukocytoclastic vasculitis according to a skin biopsy specimen, with histopathologic evidence of IgA deposition by DIF. Statistical analyses were performed using a χ(2) test to compare prevalence among each clinical manifestation.

RESULTS: There was a significant correlation between IgM deposition by DIF and renal involvement (χ(2) = 5.23, P = .022). IgM deposition and complement 3 deposition by DIF showed a close relationship (χ(2) = 5.11, P = .024). There was a significant positive correlation between serum IgA and C-reactive protein levels (Spearman's rank correlation coefficient = 0.35, P = .044).

LIMITATIONS: These findings should be validated in larger studies. Renal biopsies were not done to confirm the presence of nephritis.

CONCLUSIONS: This study suggests that IgM deposition in palpable purpura based on DIF provides an indicator of nephritis in adult patients with HSP. We believe that IgM deposition could be related to the pathogenic factors that trigger the development of renal involvement.