Multiple cutaneous leiomyomas in the perineum of a horse.

This is a case study report in which a 14-year-old Saddlebred stallion horse developed multiple skin growths in the perineum area. Surgical excision and subsequent microscopic investigation identified these growths as cutaneous leiomyomas (benign smooth muscle tumors), a condition not previously reported in horses.

Horse’s Clinical Presentation

• The 14-year-old Saddlebred stallion noticed changes in its perineum area over a span of five years. During this period, multiple skin growths, or masses, have appeared.
• The size of these masses varied, ranging from 3mm to 9mm in diameter.
• These formations were non-ulcerated, causing no pain or itchiness to the horse.

Diagnostic Investigations

• The researchers surgically removed three of these skin masses for microscopic examination.
• Observations showed that they were dome-shaped or nodular and located in the superficial layer of the skin, known as the dermis.
• The masses were composed of bundles of plump, spindle-shaped cells arranged without a particular order. This shape and arrangement are common in muscle tissue.

Molecular Analysis and Conclusion

• For further confirmation of the nature of these masses, researchers performed immunohistochemical testing. The tumor cells were exposed to monoclonal antibodies that bind to specific muscle proteins — desmin, muscle-specific actin, and smooth muscle actin.
• Positive reactions confirmed the smooth muscle origin of the tumors, leading to a diagnosis of cutaneous leiomyomas.
• This type of multiple skin leiomyomas, stemming from smooth muscle tissue, has not been previously reported in horses, making this a noteworthy case in equine veterinary literature.