Histologic Interpretation of Cutaneous Biopsies from Dogs with Dermatologic Disorders

Abstract

Clinical and histologic data were correlated on skin biopsies from 238 dogs with various cutaneous disorders. Biopsies from normal dogs were used to establish normal histologic anatomy. Seborrhea was characterized by acanthosis, mild hyperkeratosis or parakeratosis, and mild mixed inflammatory cell infiltration. Dogs with allergic dermatitis had similar epidermal changes; however, dermal edema and pronounced mast cell infiltration distinguished this group. Biopsies from dogs with pyoderma revealed intense purulent inflammation of either the epidermis or hair follicles. Lesions of demodectic acariasis were most similar to those in the pyoderma group; specific diagnosis was based upon the presence of mites in follicles. Cutaneous lesions of hypothyroidism were classified into two categories—classical and seborrheic. The more common classical form was characterized by atrophic telogen phase hair follicles and marked hyperkeratosis of the external root sheath. Inflammation was absent. In the seborrheic form, telogen phase hair follicles were associated with acanthosis and mild mixed inflammatory cell infiltration. Hyperadrenocorticism was marked by more consistent epidermal and adnexal atrophy, telogen phase follicles, and hyperkeratosis of the epidermis and follicular root sheath. Dermal mineralization or decreased dermal thickness, or both, occurred in seven of 11 dogs (60%) with hyperadrenocorticism.