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Thymoma in Cats

The thymus is a small glandular organ located in front of the heart. Its special function is to serve as a reservoir for the production and maturation of T lymphocytes, white blood cells that make up an important part of the body's immune system. A thymoma is a tumor originating from the epithelium  of the thymus (the layer of tissue covering the thymus). Thymomas are rare tumors in cats and are mainly associated with myasthenia gravis, a severe autoimmune disease which causes certain muscle groups to tire easily.

Symptoms and Types

• Coughing
• Increased breathing rate
• Trouble breathing
• Cranial caval syndrome -- a side effect of heartworm infestation, which often leads to swelling of the head, neck, or forelimbs
• Myasthenia gravis, a neuromuscular disease that leads to muscle weakness, enlarged esophagus, and frequent regurgitation

Causes

• Unknown

Diagnosis

Your veterinarian will perform a thorough physical exam on your pet, taking into account the background history of symptoms and possible incidents that might have led to this condition. A complete blood profile will be conducted, including a chemical blood profile, a complete blood count, a urinalysis, and an electrolyte panel. 

Thoracic X-rays are standard for breathing related conditions. The resulting images may show a cranial mediastinal mass (a mass between the lungs), pleural effusion (build-up of fluid in the lungs due to aspiration pneumonia) and megaesophagus. 

A blood test for antibodies to acetylcholine receptors (a neurotransmitter causing muscles to contract) should be performed to rule out myasthenia gravis. A tensilon test can also be used to test for myasthenia gravis. 

A fine-needle aspirate of the mass will show mature lymphocytes (white blood cells) and epithelial cells (cells forming in the outside layer of the thymus gland).