Aloha! You're speaking to Dr. Michael Salkin
I'm sorry that your question wasn't answered in a timely manner. I believe that you're seeing facial muscle
wasting as evidenced by Sophie's temporal muscles atrophying. Masticatory muscle myositis (MMM) will usually cause a bilateral wasting of either or both the temporal and masseter muscles but we expect to see a painful swelling of these muscles prior to wasting. Dogs will become so painful as to resist opening their mouth. If you haven't seen such pain and swelling, the diagnosis of MMM should be circumspect.
Other causes of facial muscle wasting include idiopathic (unknown cause) polymyositis
, multiple dystrophy, dermatomyositis (skin lesions seen as well), infections (Toxoplasma, Neospora, protozoal myositis), and neoplasia (cancer). These etiologies can be a challenge to clarify requiring muscle biopsies, assessment of serum antibodies against type 2 myofiber muscle fibers (MMM), and serologic titers against infectious agents.
Her change in behavior
is likely to have resulted from her systemic illness. Her localized muscle wasting is just one symptom of that illness. Medical disorders frequently induce behavior changes and those disorders need to be well-managed before the behavior abates or should be addressed in a behavioral manner - reconditioning, counterconditioning, etc.
Please respond with further questions or concerns if you wish.