Synovial Histiocytic Sarcoma of the Bicipital Tendon in a Horse. Morales Yñiguez FJ1, Oakes AE2, Gudehus T2. 1Louisiana State University, Baton Rouge, LA; 2Purdue University Centaur Equine Specialty Hospital, Shelbyville, IN.
Reasons for Performing the Study: Histiocytic sarcomas have been described as a primary lesion in periarticular tissues of large appendicular joints, most commonly diagnosed in dogs. To our knowledge, there is only one published case in horses described as histiocytic sarcoma of the nasal cavity.
Objective: To describe a case report of synovial histiocytic sarcoma in a bicipital tendon of a horse.
Methods: A 14-year-old Walking Horse gelding with a history of chronic lameness in the right forelimb of approximately 14 months of duration. During initial lameness exam, bicipital bursitis and tendonitis of the bicipital tendon were diagnosed. After unsuccessful medical treatment, bicipital bursoscopy and tenectomy of the bicipital tendon were performed. The transected biceps tendon was submitted for histopathology and immunohistochemistry due to an abnormal amorphous appearance.
Results: Proliferative synovitis with synovial histiocytic sarcoma. Based on the severity of the lameness, and tumor malignancy, a poor prognosis was confirmed and humane euthanasia was elected.
Discussion: Histiocytic sarcoma is an uncommon neoplasm of mature histiocytes with very poor outcomes; earlier diagnosis could improve the quality of life. Study Limitations: By owner decision, a necropsy was not performed. We cannot rule out metastatic tumors in other locations. Scientific or Clinical Relevance: The origin of this type of tumor is still unknown in horses. It is an incentive for other veterinarians to pursue further diagnostics for persistent lameness.