What it is
The muscles that close the jaw, on top of the head and in the cheeks, are built from a special type of muscle fibre found nowhere else in the body. In masticatory muscle myositis, the immune system makes antibodies against these fibres, and the muscles become inflamed. The rest of the body's muscles are left alone, which is why the trouble stays in the head and jaw.
The disease can come on suddenly, with swollen, painful muscles, or creep up slowly and quietly. If the inflammation lasts, the muscle fibres are gradually replaced by stiff scar tissue, the head looks bony and sunken, and the dog may no longer open its mouth fully.
A dog with a sore jaw may drop food, eat slowly or turn away from hard chews and tug games. Soft toys and unhurried mealtimes make everyday life easier, and watching how wide your dog opens its mouth to yawn or pick up a ball shows you how the jaw is doing.
Signs you may notice
- Struggles to open its mouth
- Pain when the head is touched
- Swollen cheeks or forehead
- Drops food or eats slowly
- Sunken head and eyes
- Avoids chewing toys
The dog may avoid eating or chewing, react with pain when you open its mouth or touch its head, and the muscles on top of the head and the cheeks may swell. Later the head can look sunken, the eyes sit deeper, and the dog can no longer open its mouth wide.
When to see a vet
Book a vet visit soon if your dog has trouble opening its mouth, flinches when you touch its head, or the muscles on its head swell or shrink. Go the same day if your dog cannot eat or drink.
This is general information, not veterinary advice. For your own dog's health, tests and treatment, see a vet.