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Why is my dog struggling to open its mouth and jaw is sunken?

Updated On September 23rd, 2025

Pet's info: Dog | Mixed Breed | Male | unneutered | 1 year and 3 months old

My dog is having a problem opening its mouth. He can't seem to open it more than an inch. Muscles around the jaw and the top of its head are sunken in

2 Answers

Most Helpful Answer

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Answered By Dr. Melanie, BVSc MS

Veterinarian

Published on September 4th, 2016

Poor Marley! It sounds like he may be suffering from an autoimmune disease called masticatory muscle myositis (MMM). This inflammatory disease affects the chewing muscles in the dog, and causes the muscle around the mouth to atrophy. It becomes painful for the dog to open their mouth. This can be treated with high dose steroids, which can be prescribed by your vet. This condition can cause dogs to not eat and lose weight, so I would take Marley into your vet as soon as you can.

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22Pet Parents found this answer helpful

Other Answers

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    Answered By Dr. Massimo Orioles, DVM, Cert AVP, MRCVS

    Veterinarian

    Published on

    That could be due either to a masticatory muscle myositis (so basically an autoimmune inflammation more likely considering the age) or a temporal and mandibular muscle atrophy due to denervation (less likely but possible). The way to diagnose the first disease goes through the biopsy of the muscles and a blood test specific for this disease (if the blood test is highly positive the biopsy is not needed). The treatment is based on steroids basically.

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    9Pet Parents found this answer helpful

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