If a melanoma spreads to a horse's central nervous system, treatment isn't likely to be effective. | Photo: The Horse Staff

Q: There’s a gray lesson horse in his early 20s at my barn who has had melanoma growths under his tail for years. They don’t seem to cause him discomfort, and his riders always keep that area very clean. In the past week, however, he’s started losing his balance occasionally and is showing neurologic signs. The vet is coming out to see him, but is it possible that the melanoma has spread to his central nervous system? If so, is there anything that can be done? —Ashley, via e-mail

A: Your question is a good one, given this horse’s age and his long history of melanomas. The short answers to your questions are:

1. Yes, metastasis (i.e., spread) of the melanomas to his central nervous system is certainly possible, and
2. If metastasis has occurred, no treatment is likely to be effective.

A thorough veterinary physical exam can confirm that the horse is truly ataxic (incoordinated), rather than lame from a non-neurologic cause. If actual ataxia exists, a focused neurologic exam can define the precise location of a central nervous system lesion. This information can help generate a realistic list of possible causes, or differential diagnoses