Diagnostic Exercise: Severe Bilaterally Symmetrical Alopecia in a Horse

In 2011, a case study of a 9-year-old Tennessee Walking Horse gelding with severe bilaterally symmetrical alopecia was reported. The horse, which had noninflammatory alopecic areas and a history of suspected hypothyroidism, showed normal T4 and slightly depressed T3 thyroid levels. Microscopic examination revealed lymphocytic infiltration in various parts of the hair follicles and mild lymphocytic dermatitis with budding yeasts consistent with Malassezia spp. The final diagnosis was alopecia areata (AA) with Malassezia dermatitis. The study suggests that AA may predispose horses to Malassezia infections, which typically occur in immunocompromised skin, although the infection in this case was found in atypical locations. The document did not report the number of horses studied beyond this single case and did not declare any conflicts of interest or financial support.