Generalized dermal dysplasia and perifollicular mucinosis in a dog.

Multiple nodules 0.5-2 cm in diameter were observed in the dorsal skin of a 1.5-year-old male castrated mongrel dog. Histopathologically, perifollicular mucinosis and clusters of small cells with a dense, round nucleus and scant cytoplasm were seen. The small cell clusters were present in the dermis near the epidermal basal layer or surrounding hair follicles. These cells demonstrated different staining patterns for vimentin and keratin depending on their location; ultrastructurally, they were poor in organelles and connected to each other with cytoplasmic projections. These findings suggested that they were immature epithelial cells. The case was diagnosed as generalized dermal dysplasia and perifollicular mucinosis.