Severe bilaterally symmetrical alopecia in a horse.

The research is about diagnosing the cause of extensive hair loss in a 9-year-old Tennessee Walking Horse. The final diagnosis indicated the horse was suffering from alopecia areata along with Malassezia dermatitis.

Detailed Investigation into the Disease

• The research involved a detailed examination of a 9-year-old Tennessee Walking Horse gelding that was presented with symptoms of extensive hair loss, affecting parts including the head, neck, shoulder, thigh, and proximal limbs. However, there were areas that remained unaffected, such as the trunk, distal limbs, pelvic area, mane and tail.
• The skin in the areas experiencing hair loss was non-inflammatory, with clear absence of exudate or crust, with the exception of the shoulder and along the back. Mild itching was observed in the horse.

Microscopic Examination of the Condition

• On microscopic examination, small to moderate numbers of small lymphocytes infiltrated the hair bulbs, inner root sheaths, outer root sheaths of inferior segments, and perifollicular regions. This level of inflammation was occasionally visible in isthmus follicular walls and apocrine glands. No impairment was observed in sebaceous glands.
• The small lymphocytes were identified as CD3(+) T lymphocytes through an immunohistochemical analysis.

Examination of Skin Regions Featuring Scales and Crusts

• When the researchers examined the epidermis from the parts of the skin that showed scales and crusts, they recorded findings of mild to moderate hyperplasia, mild lymphocytic exocytosis, and mild eosinophilic dermatitis.
• Additionally, they noticed diffuse parakeratosis, a condition characterized by irregularities in the keratinization process leading to the preservation of nuclei in the stratum corneum. The researchers also observed the presence of numerous budding yeasts, which were consistent with Malassezia spp.

Final Diagnosis of the Condition

• The final diagnosis concluded that the horse was suffering from two conditions: alopecia areata and Malassezia dermatitis. Alopecia areata is a type of non-scarring hair loss condition, and it can often lead to complete hair loss.
• On the other hand, Malassezia dermatitis is a skin condition caused by yeast, which often results in inflammation, itching, scaling, and loss of hair. The researchers proposed that alopecia areata could be a contributing underlying factor for Malassezia dermatitis in this case.