Help!! Possible muscle myositis?

I have a 11 month old American Bully Female that was born on 10/31/22.  She is extremely food motivated and tries to eat nearly everything outside (grass, plants, rocks ect).  I am hoping she outgrows this but worry sometimes about having Pica. Around July 11th, Diva and I were snacking on seedless watermelon all day when in the evening I handed her a piece and when she tried to open her mouth she yelped.  She stopped eating all food (including human) because I could tell it hurt her to open her mouth.  Usually I can probe and open her mouth with ease and she would not allow me to do so. She also would hack every so often (not frequently) and drooled from the right side.  Swelling was also noticed under her eye. After attempting to she literally avoided me for the next 48 hours. 7/13 I took her to the Vet, there was no swelling in the gumlines nor evidence of any impacted teeth.  I have a beautiful landscaped yard but thought about her being poisoned by landscapers or her allergies (they flare up really bad, one of the plants does not agree with her, hives and welts).  X rays were inconclusive so she was put on Clavomox and Rimadyl.  She progressively got better and 3-4 days later was back to normal.  Blood work inconclusive. Fast forward to two days ago.  My pup was sitting on my roomates couch and yelped and jumped off the couch, since then she cannot open her mouth except very slightly and doing any further causes her imense pain.  She is lethargic and not herself.  She is eating soft food that I got her but it has to be mush.  Her eyes are also having a allergic reaction as well, and she drools on the right side, every so often. I took her back to our Vet and he wanted to go on same plan of pain killer and antibiotics, i asked if we could test for muscle myositis, as she is experiences several of the symptoms.  Plan was if she wasnt better to then put her to sleep to check her mouth after 3/4 days as well as dental x rays. Vet seemed to not be aware of the disease nor have much experience with it.  He charged me 250.00 for a blood panel (that he told me she was fine) for me to find out the none of the tests for classifciation and diagnosis of Myositis were even ordered.    Creatine Kinase and Anti-Pm/Sci-100 Antibody as well as Aldolase are essential in coming to a conclusion. I love my vet but I wonder if he lacks the experience, or if anyone else has any suggestions on what I could be dealing with.  Please help!  My pup is in pain. I have pictures of all x rays, blood labs, and plan of care on file if any more information is needed.  Appreciate any help    

Hello - this is a pretty unusual presentation and as you seem to get on with your vet, I wouldn't necessarily worry about their experience level. Even old vets like me, when they're practising every day, experience plenty of cases they've never seen before. Even if they have never dealt with masticatory myositis and have to look up what to do to diagnose it or rule it out, whats important if whether they take the trouble. So, you could ask them to speak to a pathologist about the tests required to diagnose masticatory myositis - or if they don't think that's necessary, then you could ask them why not / whether they agree that it may be a possibility.  If not, they must have some idea as to what the next diagnostic step ought to be. Off the top of my head, I can't think of many diseases that would present as pain on opening the mouth, which would also show up on a blood test, so you could ask about the purpose of the blood test and how it moved things fwd (there may be a specific blood test for masticatory myositis available - if so, does it catch every case? - or if only routine bloods were taken, they might have cleared the way for a GA or certain pain killers to be used).  I find that its useful to ask whats on the differentials list as it stands - 'what could this still be at this stage?' - and then how they intend to narrow the list down from here.   You don't mention how many times you have seen your vet - the first time, I can completely understand that they might not yet have a diagnostic pathway clear in their head.  If they don't see you again, they may assume that things have got better.   Therefore, making an appointment and asking directed questions to establish a plan going forward ('how can we arrive at a next step?'   'Would you be prepared to test for masticatory myositis?  What is stopping this from happening?  What else needs to be ruled out?') may prove to be a good way forward.