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Key takeaways

Masticatory myositis is a condition of unknown origin where the muscles needed to chew become inflamed, making it painful to open the mouth or eat food.

  • It is so rare in cats that there is no clear consensus among the veterinary community as to whether it is a feline condition at all
  • An animal with masticatory myositis will not open its mouth, or present with discomfort doing so, leading to weight loss
  • Masticatory myositis is often a clinical diagnosis, based only on the presenting symptoms, but specific blood tests, muscle biopsies, and electromyography may be used to confirm the diagnosis
  • Treatment may include oral steroids, immunosuppressive medications, and surgery
  • Prognosis in cats is undetermined
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A closer look: Masticatory Myositis in Cats

Masticatory myositis requires prompt medical treatment, as it is a painful condition and interferes with eating. The condition is unlikely to be life-threatening, but as eating becomes painful weight loss and nutritional deficiencies may develop.

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Risk factors

Chronic masticatory myositis results in more obvious weight loss as reduced food intake has a more visible effect on the body. The muscles of the mouth may atrophy with disuse, making it even more difficult to open the mouth.

Possible causes

Masticatory myositis - if it occurs in cats at all - is caused by an immune-mediated response of unknown origin which attacks the muscles used in chewing (mastication), causing them to become inflamed and irritated.

Main symptoms

Acute masticatory myositis presents as an unwillingness or inability to open the mouth. While cats are often stoic when dealing with chronic pain, affected cats may be less vocal than usual, leave food uneaten, and fail to groom themselves.

Testing and diagnosis

Masticatory myositis is often diagnosed based only on the typical clinical signs. Blood tests, electromyography, and biopsies can confirm the diagnosis, and diagnostic imaging can show changes in the affected muscles.

Steps to Recovery

Liquid dietary supplementation may be required to ensure basic nutritional needs are met. Oral steroids are used to treat the condition until symptoms resolve. Once the mouth can open normally, steroids are gradually tapered off over a period of months.

Little is known about masticatory myositis in cats, but in dogs it has a positive prognosis, although relapse is possible after treatment. Steroids are gradually weaned off over a period of up to six months after symptoms cease, but dosage may need to resume if symptoms return.


This condition is idiopathic, making it difficult to prevent. It is not contagious.

Is Masticatory Myositis in Cats common?

Masticatory myositis is very rare in cats. There are so few cases reported in cats that there is a lack of consensus in the veterinary community regarding its existence in cats at all.

Typical Treatment

  • Oral steroids
  • Dietary supplementation


Joseph Harari - Writing for MSD Veterinary Manual
Marco Armellini, Lluís Sánchez, Andrea Lorek, G Diane Shelton, Luisa De Risio - Writing for JFMS Open Reports
Wendy Brooks - Writing for Veterinary Partner

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