Texas Equine Veterinary Association

www.texasequineva.com • Page 18 clumped chromatin. Mitotic figures were frequent (>4/10 Hpf ) and bizarre. e cytoplasm was scant and lightly basophilic. e final diagnosis was lymphosarcoma. Discussion Equine lymphosarcoma occurs in mediastinal, alimentary, multicentric, and cutaneous forms, although combinations of these forms occur frequently.1 Neoplastic involvement of the thoracic structures or pulmonary parenchyma per se is rare in horses and occurs at a prevalence rate of 0.15 to 0.62. In addition to being the most common thoracic neoplasm, lymphoma is also the most common tumor of the equine hematopoietic system.2 Horses affected with mediastinal lymphoma are young to middle- aged (mean age of 10 years) and exhibit weight loss, ventral edema, jugular distention caused by the presence of a mediastinal mass, tachypnea, or respiratory distress caused by pleural effusion secondary to compression of vessels. oracocentesis may yield a modified transudate or nonseptic exudate, but neoplastic cells- lymphoblasts with mitotic figures-are not consistently found.2 Ideally, a transtracheal wash would have been done on presentation, but since the horse presented on a Friday aernoon and culture results would have required a minimum of five days, initial treatment was started. Pleural effusion is found more commonly with coccidioidomycosis but has also been reported in cases of cryptococcosis and blastomycosis. An elevated titer in a clinically ill animal strongly supports the diagnosis of a C. immitis infection.2 In this case, a negative titer was used to rule out a fungal infection. oracic radiographs may have helped identify a mediastinal mass, but we do not have a machine big enough to do so at our clinic. e clinical course of the disease, from onset of signs until euthanasia, is oen rapid and may be less than eight weeks for most cases. ere is a report of a successful treatment of a mixed-cell mediastinal lymphoma using cytarabine, cyclophosphamide, and prednisolone.2 In this case, the horse was euthanized six weeks aer the initial presentation for weight loss. References: 1. Scarratt WK, Crisman MV. Neoplasia of the Respiratory Tract. Veterinary Clinics: Equine Practice 1998; 14,3: 451-473. 2. Ainsworth DM, Cheetham J. Disorders of the Respiratory System. In Reed SM, Bayly WM, Sellon DC. Equine Internal Medicine. 3rd ed. St. Louis: Elsevier. 2010; 290-371.

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