Masticatory Muscle Myositis (MMM) in Dogs
Masticatory Muscle Myositis (MMM) is a high-severity autoimmune condition that can affect dogs of all ages and breeds. MMM is an immune-mediated inflammatory disease targeting the masticatory muscles (temporalis and masseter), which have a unique muscle fibre type (2M) not found elsewhere in the body. It causes pain, trismus (jaw locking), and muscle atrophy. It is documented across 5 breeds, though prevalence and severity can differ significantly between them. It typically becomes apparent at 3-8 years. Early signs to watch for include jaw pain and reluctance to eat, inability to open mouth (trismus), swollen then wasted temporalis muscles, and exophthalmos (if acute swelling). When treatment is required, costs are estimated at £500-£2,500 depending on severity, location, and the specific intervention needed. This page covers symptoms, treatment options, and preventive steps — along with breed-specific information where available.
Signs & Symptoms
The following symptoms are commonly associated with Masticatory Muscle Myositis (MMM) in dogs. If your dog displays several of these signs, consult your vet promptly — early diagnosis typically leads to better outcomes.
- Jaw pain and reluctance to eat
- Inability to open mouth (trismus)
- Swollen then wasted temporalis muscles
- Exophthalmos (if acute swelling)
- Weight loss
Treatment Overview
High-dose immunosuppressive prednisolone is highly effective if started early. Long-term tapering doses are needed to prevent relapse. Early treatment before muscle fibrosis develops gives the best outcomes.
Typical onset: 3-8 years
Prevention & Screening
While not all cases of Masticatory Muscle Myositis (MMM) can be prevented, the following steps reduce risk or enable earlier intervention:
- No proven prevention
- Prompt investigation of jaw pain or swelling
Estimated Treatment Cost
Treatment for Masticatory Muscle Myositis (MMM) is estimated at £500-£2,500, depending on severity, the specific intervention required, and your location. Costs may be higher for surgical procedures or ongoing management. Comprehensive pet insurance covering this condition is strongly recommended.
Breeds Affected by Masticatory Muscle Myositis (MMM)
The following 4 breeds are documented as being susceptible to Masticatory Muscle Myositis (MMM). Click any breed to view breed-specific information about this condition, including prevalence and recommended screening.
Looking for more information? Browse all dog health conditions or explore the health guides for in-depth breed care advice.