A concomitant case of giant cell arteritis and microscopic polyangiitis with hemoperitoneum by rupture of the gastroepiploic artery.

Giant cell arteritis (GCA) mainly involves large-sized arteries, while microscopic polyangiitis (mPA), characterized by pauci-immune necrotizing vasculitis, mainly affects small-sized vessels. We report a very rare concomitant case of GCA diagnosed by temporal artery biopsy and mPA with a high titer of myeloperoxidase antineutrophil cytoplasmic antibody, exacerbation of interstitial pneumonia, and suspected rapidly progressive glomerulonephritis. The patient died by sudden rupture of the gastroepiploic artery (medium-sized vessel), which may have been triggered by GCA and/or mPA.