Cutaneous lesions after intestinal bypass.

Twenty-three of 81 intestinal bypass patients with episodes of bypass enteropathy had papulopustular or nodular skin lesions. Histologic examination of the dermal lesions showed various forms of vasculitis in nine of 14 subjects. In six of 11 patients examined by immunofluorescent microscopy, both the lesions and uninvolved sun-exposed skin areas had immunoglobulin and complement deposits in linear or granular patterns in the dermoepidermal line, giving the appearance of a positive lupus band test. Skin lesions resolved with spontaneous improvement of bypass enteropathy or in response to metronidazole therapy. After the bypass was dismantled, the eruptions disappeared permanently, and previously positive lupus band tests became negative. The skin lesions were frequently observed in association with arthritis, suggesting an immune-complex mechanism, probably originating in "blind loop" bacterial overgrowth.