Noninflammatory, nonpruritic alopecia of horses.

Noninflammatory, nonpruritic alopecias are uncommonly encountered in the horse. Alopecia areata, an apparently autoimmune hair follicle bulbitis produces focal, multifocal to widespread hair loss. The skin is otherwise normal. Diseases that can mimic the widespread hair loss associated with alopecia areata include telogen and anagen effluvium, seasonal alopecias, follicular dysplasias (including color dilution alopecia), various nutritional deficiencies and chemical toxicosis, and diseases that result in defective hair shafts (eg, trichorrhexis nodosa and piedra). These problems are differentiated by history, physical examination, trichography, and skin biopsy. Most are cosmetic diseases that do not have predictably effective therapies.