"Masticatory Muscle Myositis in Dogs

"Masticatory Muscle Myositis in Dogs

Health & Safety

Masticatory muscle myositis is a serious condition that needs to be treated early if the prognosis is to be positive. The disorder negatively impacts a dog's jaw muscles and is a painful condition that results in dogs being unable to eat or drink. Masticatory muscle myositis or MMM, is a condition that affects one breed more than others with young dogs being more at risk although any dog can develop the condition at any stage of their lives.

Breed Most at Risk

Research has established that certain breeds appear to be most at risk of developing MMM although as previously mentioned, any breed can suffer from the condition at any stage of their lives. The breeds known to be most at risk are as follows:

  • Doberman Pinschers
  • German Shepherds
  • Labrador Retrievers
  • Golden Retrievers
  • Cavalier King Charles Spaniels - young dogs tend to be most at risk

In Labrador Retrievers and Cavalier King Charles Spaniels, studies have shown the breeds may be predisposed to developing the condition due to genetic link. It is also worth noting that the condition affects male and female dogs when they are around 3 years old although in some cases puppies as young as 4 months old can be affected by MMM. The good news is that the earlier the condition is diagnosed and treated, the better the outcome.

Symptoms Associated with the Condition

There are certain symptoms associated with MMM which are quite obvious, but there are times when the signs of there being something wrong are more subtle and therefore can go unnoticed. The symptoms most commonly associated with the disorder include the following:

  • Swollen muscles around the mouth
  • Pain when trying to eat or drink
  • An inability to open the mouth which is a condition known as trismus
  • Difficulty picking up a ball or other object
  • Muscles begin to atrophy around the mouth in the latter stages
  • Sunken/protruding eyes
  • A reluctance to play

The Causes

Masticatory muscle myositis is known to be a unique type inflammatory myopathy. It is an autoimmune disorder that negatively impacts a dog's jaw muscle because their antibodies target these specific muscles. However, the actual causes why some dogs are more prone to developing or inheriting the disorder remains unknown although there is some thought that T-cells are involved and that the antibodies start to react to fight off some sort of infection or condition which could include the following:

  • Rheumatoid arthritis
  • Pericarditis

Studies also suggest that genes can play a key role in whether a dog develops the condition and research has also indicated that this is extremely complex which in short means more research would be needed to identify the exact causes. However, in breeds known to be predisposed to developing MMM, it is known that there are certain triggers which includes the following although very often the exact trigger often remains unknown:

  • Viral infections
  • Bacterial infections
  • Vaccinations
  • Hormones
  • Allergens
  • Stress
  • Certain medication
  • Environmental toxins

Diagnosing the Condition

A vet would ideally need to have a dog's full medical history and their ancestry too which all helps make a diagnosis. The more information a vet can be given the better. The vet would thoroughly examine a dog suspected of suffering from MMM and would typically recommend carrying out the following tests to confirm their diagnosis:

  • A complete blood count
  • A full biochemistry profile to establish creatine kinase levels
  • Neurological tests
  • 2M antibody test
  • X-rays of a dog's jaw

Treatment Options

The earlier a dog's condition is diagnosed and a treatment plan is set in place the better the prognosis tends to be simply because if the condition reaches a chronic stage, the harder it is to treat successfully. Vets would treat a dog suffering with MMM with immunosuppressant drugs to prevent any more damage from being done by a dog's own immune system. The type of treatment a dog is given depends on the severity of their condition. Sadly, the disorder often goes unnoticed until it is in its latter stages which means more damage is done to their muscles and it can even negatively impact their optic nerves which can lead to blindness.

Should a vet be able to treat a dog successfully for MMM, the dog would need to be treated for at least four months with some having to remain on their medication for the rest of their lives which means that side effects associated with their medication must be taken into account.


The prognosis for dogs suffering from MMM depends on the severity of their condition and at which stage they were diagnosed and treated for the disorder. As previously mentioned, the earlier the condition is treated the better the outcome. The problem is that some dogs experience a relapse even during a treatment which makes it harder to successfully treat them.

Breeding Recommendations

Any dog known to have suffered from MMM should not be used for breeding purposes which helps reduce the risk of any offspring developing the condition through a genetic link. There is a 2M antibody blood test available which was developed by researchers in America in 2004 and breeders should have all their dogs tested before using them in a breeding programme.

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