Hypocomplementemic cutaneous small vessel vasculitis in a patient with IgG4-related disease.

A 62-year-old man was diagnosed with IgG4-related disease based on multiple sites of lymphadenopathy, lymph node biopsy, and elevated serum levels of IgG4. Hypocomplementemia was also observed. During admission, he was referred to our department complaining of multiple areas of purpura on the lower legs. Histological examination revealed leukocytoclastic vasculitis with fibrinoid necrosis, neutrophil infiltration, and nuclear dust in the upper dermis. To date, only a few cases of cutaneous vasculitis have been reported in IgG4-related disease, all of which showed hypocomplementemia. The role of IgG4 in the etiology of leukocytoclastic vasculitis in IgG4-related disease remains unknown and further studies are necessary.