Masticatory Myositis?

Hi vets - looking for some advice 🐕 My 9 year old lab pit mix was put on prednisone and gabapentin for neck pain 2.5 weeks ago. I noticed that when I started to taper the prednisone down, he seemed to become sad again so I took him to the vet. The vet noticed the muscles in his face atrophied a bit and he wouldn’t let her open his jaw. It’s been a few weeks since he has been able to yawn or play with toys, but I didn’t notice his face until the vet mentioned it (she also did not realize the muscle loss during his exam 2 weeks ago). She suspects Masticatory Myositis. I know prednisone causes some muscle atrophy as well, so could it be that? Or maybe something wrong with a tooth? It’s just all confusing because he was dealing with some neck pain and now all of a sudden he can’t open his mouth more than an inch and he seems depressed. He also cannot be put on Prednsione anymore because his ALP levels are too high since he started it 2.5 weeks ago. I feel so bad for him. He’s just laying next to me and I can sense he’s in pain 🥺 If it is MMM, will other course of treatments help?

Hello   I'm afraid that I can't tell from your post how far your vet is along with diagnosing masticatory myositis in your dog.  Was it mentioned as a possibility, or has a biopsy been taken and a diagnosis been made that way, or can a strong assumptive diagnosis be made?  Differential diagnoses for Masticatory Myositis - that is, other things that look similar - include cancers and lumps affecting nerves of the jaw (in particular, the trigeminal nerve of the face), joint inflammation (particularly of the TMJ, which is the 'jaw' joint e.g. arthritis and ankylosis), tumours of the ear and tetanus.  It sounds as  though, in this case, there may be a trade-off between giving steroids to ease the jaw and causing an inflammatory reaction in the liver.  An article in the Veterinary Times, dated September 2013, does suggest that other immunosuppressive agents can be used.  Good questions for your vet include, 'How certain is this diagnosis?'  'What other treatments could we try' and if still unsure, 'Is there an expert we can ask for more information?'  - as MM is a relatively unusual disease and vets in general practice don't see it particularly often.

Of course, the question, 'What are the risks and benefits of continuing to use steroids' will perhaps help to clarify the situation there, too.  Wishing you all the best and please do let us know what happens next.