Signs of sympathetic denervation associated with a thoracic melanoma in a horse.

The study reports on a 20-year-old horse showing symptoms of sympathetic denervation, which was likely caused by a thoracic melanoma.

Symptoms and Diagnosis

• The horse, a Thoroughbred-Percheron gelding, exhibited cutaneous hyperthermia (excessive heat on the skin) and sweating on the right side of its body. These symptoms were localized to a specific area and did not include other typical signs of Horner’s syndrome.
• The pattern of the hyperthermia and sweating suggested that sympathetic denervation had occurred. Sympathetic denervation is the loss of sympathetic nerve supply to various organs and tissues. In this case, it is believed to be localized to the cervicothoracic ganglion, a network or cluster of nerve cells located in the neck and chest region.
• Further examination with thoracic radiographs revealed increased density in the craniodorsal thorax – the upper, front part of the chest. This abnormality helped to confirm the suspicion of a medical issue within the thoracic cavity.

Evaluation and Treatment

• Cytologic evaluation, a detailed study of cells, was conducted on a sample of pleural effusion – excess fluid that forms between the layers of the pleura, the thin membrane that lines the chest cavity and surrounds the lungs.
• The evaluation revealed the presence of mesothelial cells containing melanin and cells that suggested melanocytes or melanoblasts. Both melanocytes and melanoblasts are involved in the production of melanin, the pigment that gives color to skin, hair, and eyes. Their presence in the pleural fluid indicates a potential melanoma.
• Despite treatment with oral cimetidine and intrapleural cisplatin, the symptoms did not improve. Cimetidine is a common medication for reducing stomach acid, often used in treatment for stomach ulcers in horses, while cisplatin is a chemotherapy drug often used to treat various forms of cancer.

Conclusion

• Although a formal necropsy (autopsy for animals) was not performed, the clinical findings, including symptoms and cell evaluation, suggested a diagnosis of thoracic melanoma involving the cervicothoracic ganglion.
• This case underlines the importance of thorough clinical evaluation in horses presenting with distinct, localized symptoms in order to accurately diagnose and aim to treat possible severe health conditions such as melanoma.