Extramedullary plasmacytoma in a horse with ptyalism and dysphagia

A Clydesdale mare was examined for weight loss, inappetence, ptyalism, and dysphagia. The main abnormality revealed by serum biochemistry was a marked hyperglobulinemia, and protein electrophoresis revealed a monoclonal gammo pathy in the gamma region. The urine was positive for Bence Jones proteins. These findings suggested a plasma cell tumor. The neoplasm could not be lo cated with extensive antemortem examination. At postmortem, neoplastic cell s morphologically compatible with plasma cells and positive for equine IgG with imunoperoxidase staining infiltrated the pericardium, mediastinal stro mal tissues, adrenal glands, meninges, atrioventricular valves, aorta, abdo minal and thoracic fat, and nerves, including the trigeminal nerve. The neo plastic cells invading the cranial nerves were responsible for many of the presenting signs.