Diffuse cutaneous mastocytosis in a newborn calf.

Previously reported cases of congenital cutaneous mast cell tumours in calves were characterized by multiple discrete nodules. The calf presented herein is, to the authors' knowledge, the first documented case of congenital diffuse cutaneous mastocytosis. The entire skin was thickened and wrinkled with particularly prominent skin folds on the head, ventrum, and legs. Histological examination of two haired skin specimens (eyelid, muzzle margin) revealed that the dermis was diffusely infiltrated by sheets of neoplastic mast cells.