Extramedullary plasmacytoma in a horse with ptyalism and dysphagia.

This study investigated a case of a Clydesdale mare exhibiting symptoms of ptyalism (excessive drooling), dysphagia (difficulty swallowing), weight loss, and lack of appetite, which were later attributed to a plasma cell tumor. The tumor, diagnosed as extramedullary plasmacytoma, could not be located during the horse’s life. However, post-death examination revealed its presence in various body tissues and organs, significantly affecting the nervous system.

Identifying Symptoms and Initial Test Results

• The Clydesdale mare presented several symptoms including weight loss, inappetence (lack of appetite), excessive saliva production (ptyalism), and difficulty swallowing (dysphagia).
• Serum biochemistry revealed an abnormal increase in globulins, proteins produced by the immune system. Protein electrophoresis, which separates proteins based on their size and charge, showed a monoclonal gammopathy within the gamma region. This finding suggested that a type of white blood cell, known as plasma cells, was overproducing a specific type of protein.
• The horse’s urine tested positive for Bence Jones proteins, which are usually found in certain types of cancer, like multiple myeloma. These findings pointed towards the presence of a plasma cell tumor.

Postmortem Examination and Diagnosis

• The tumor was not located during the horse’s life despite extensive examination. It was only discovered during postmortem examination.
• The postmortem examination revealed the presence of neoplastic cells that appeared to be plasma cells in several body tissues and organs. These cells were found in the pericardium (surrounding the heart), the mediastinal stromal tissues (connective tissues in the chest cavity), adrenal glands, meninges (protective layers covering the brain and spinal cord), the heart’s atrioventricular valves, the aorta, abdominal and thoracic fat, and various nerves.
• The tumor cells were confirmed to be plasma cells as they tested positive for equine IgG, an antibody produced by plasma cells, under immunoperoxidase staining. This type of cancer is known as an extramedullary plasmacytoma.
• Among the invaded nerves was the trigeminal nerve, which is responsible for sensation in the face and motor functions such as biting and chewing. The invasion of the neoplastic cells into the cranial nerves could explain many of the mare’s symptoms, such as difficulty swallowing and excessive drooling.