Arrector pili muscles are present, but not enlarged or vacuolated. The low baseline T4 level might indicate, but is not diagnostic for, hypothyroidism. There are no histologic changes to suggest hypothyroidism and it is unknown if the dog was on thyroid medication at the time of biopsy. Case 30-4 . There is hair follicle atrophy with clumping of melanin in one follicle accompanied by mild intrafollicular hyperkeratosis.
Hair shafts break, and regrowth is often poor.
Follicular papules and comedones may develop, and chronic cases may exhibit hyperpigmentation. Ann Meet Am Acad Vet Dermatol and Am Coll Vet Dermatol. A macroscopic and microscopic evaluation of canine and feline skin disease. Mosby Year Book, St. Louis, MO, pp. The American Veterinary Medical Association and the American College of Veterinary Pathologists are co-sponsors of the Registry of Veterinary Pathology.