A couple of quick questions:
1. Is there any muscle loss anywhere else?
2. Is there any pain?
3. Which side of the head?
4. Is he on flea and tick preventative?
5. Any neurologic signs at all? Drooping of the eyelid, face, etc. Dropping of food? Can't see out of the eye ont he side of the face that is affected?
Ok great! Thanks for the extra information.
The muscle you are describing is called the temporal muscle. Since this is the only place that is affected, we have to assume there is something wrong with the nerve that innervates that area only. When we lose innervation to a muscle, the muscle will waste away very quickly. The nerve that innervates that muscle is called the trigeminal nerve. The things that can affect the nerve supplying a particular muscle are trauma, infection, or cancer (particularly a nerve sheath tumor).
The disease you read about is called Masticatory Muscle Myositis. This means inlammation of the muscles of mastication (chewing). This usually doesn't affect just one side of the face but it is possible. This is an autoimmune disease and something I think should be considered here. There is a test called a 2M titer test I believe.
If that test comes back normal, you may want to consider a CT or MRI of the area to get a definitive diagnosis though I am not 100% sure if treatment options would be available. If you decide to go that far, it might be worth it to see a specialist in neurology.
For what it is worth, I have seen one or two of these situations respond with the use of steroids regardless so that might be another option!
Hope that helps!
You're very welcome. The thing about the neurologic signs (which we aren't seeing) is that if there is a tumor of just that nerve, this might be the only sign we see. The good news with that, however, if that it likely will never cause a problem outside of the muscle loss. You are spot on with the revolution.
I wish you luck!!