A retrospective study of dysplastic hair follicles and abnormal melanization in dogs with follicular dysplasia syndromes or endocrine skin disease

A retrospective histopathological study was conducted on skin biopsy specimens from 70 dogs with follicular dysplasia syndromes and 102 dogs with endocrine skin disease. Criteria evaluated included dysplastic hair follicles, dysplastic hair shafts, and irregularities in melanization of the follicular epithelium, pilar canal, hair shaft, and perifollicular areas. Dysplastic hair follicles were found in 76% of the dogs with follicular dysplasia syndromes and 46% of the dogs with endocrine skin disease. There was a significantly higher frequency of dysplastic hair follicles and abnormalities in the melanization of the follicular epithelium, pilar canal, and perifollicular areas in the follicular dysplasia syndromes group. Although dysplastic hair shafts were almost exclusively seen only in specimens from dogs with follicular dysplasia syndromes, unique to the follicular dysplasia syndromes group was the clumping of melanin within hair shafts and the presence of dysplastic hair shafts. Histological criteria other than the mere presence of occasional dysplastic hair follicles must be used to differentiate follicular dysplasia syndromes from endocrine skin disease.