P‐40 Black hair follicular dysplasia in a dog: an ultrastructural study using transmission electron microscopy

Abstract

Black hair follicular dysplasia (BHFD) is a rare disorder in which dogs with bicolour or tricolour coats lose hair only in the black areas at an early age. Large melanin granule deposits within the hair shafts and follicles are the hallmark of this disorder, but the pathogenesis remains uncertain. A study using scanning electron microscopy has suggested that an abnormality of pigment transfer may play a role in the pathogenesis. Here, we present a BHFD dog in which the lesions were examined by transmission electron microscopy. A 3‐year‐old male mixed‐breed dog with black‐and‐white hair coat presented with a 2‐year history of alopecia in the black‐haired areas. Physical examination revealed no abnormalities other than alopecia. Skin scrapings, fungal culture, CBC, serum chemistry analysis, and endocrine tests were unremarkable. Histopathologically, no abnormality was observed in the white‐haired areas, whereas black‐haired areas showed numerous large melanin granules in hair shafts and follicles. Based on these findings, the dog was diagnosed as having BHFD. Transmission electron microscopy revealed numerous melanin clumps consisting of atypical (both in shape and size) melanosomes in the lower part of telogen hair follicles. Some melanin clumps were surrounded by a cell membrane‐like structure, in which degenerative nuclei were recognized. It is speculated that melanin clumps originate from melanin blockade. Further investigation is needed for a better understanding of the pathogenesis of BHFD. Funding: Self‐funded.