Myositis in Dogs

Veterinary reviewed by: Dr. Linda Simon, MVB MRCVS

Myositis in Dogs - Symptoms, Causes, Diagnosis, Treatment, Recovery, Management, Cost

Veterinary reviewed by: Dr. Linda Simon, MVB MRCVS

Myositis in Dogs - Symptoms, Causes, Diagnosis, Treatment, Recovery, Management, Cost

What are Myositis?

There are various types of myositis, each with different causes that range from heredity to an immune-mediated response. Such is the case with masticatory myositis, caused by antibodies targeted to attack the masticatory muscles only. As with many types of myositis, without early and aggressive treatment, muscle loss can cause severe atrophy and muscle dysfunction. This can result in conditions like blindness, an inability to eat, and an inability to walk. Lesions can occur that involve swelling, hemorrhage, atrophy, and fibrosis.

Myositis refers to a group of diseases that all share an inflammation of the muscle tissue. This condition can affect only one muscle, or an entire group of muscles, such as the masticatory muscles and the eye muscles, and can cause debilitating symptoms.

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Myositis Average Cost

From 382 quotes ranging from $1,000 - $3,000

Average Cost

$1,500

Symptoms of Myositis in Dogs

Symptoms of myositis can vary greatly, and are dependent on which muscle groups are affected.

Masticatory myositis

  • Difficulty moving jaw
  • Inability to open mouth
  • Swelling of jaw
  • Loss of muscles
  • Sunken eyes
  • Pain in jaw
  • Problems eating and drinking
  • Muscle atrophy
  • Jaw fixation
  • Anorexia
  • Weight loss
  • Blindness

Extra-ocular myositis

  • Protrusion of the eyeball
  • Swelling around eye
  • Impaired vision
  • Blindness

Polymyositis

  • Stiff walking
  • Muscle pain
  • Muscle weakness
  • Swelling in muscles
  • Loss of muscle
  • Difficulty swallowing
  • Regurgitation 
  • Breathing problems

Dermatomyositis

  • Skin lesions
  • Muscle atrophy
  • Muscle pain
  • Abnormal gait
  • Lesions on feet, ears, face and tail

Types 

There are different types of myositis found in dogs, and each is associated with a specific muscle group.

Masticatory muscle myositis – Affects the muscles found on the sides and the top of the head that are used for chewing. There is a progressive destruction of these muscles that eventually lead to a jaw fixation, and is believed to be immune-mediated. This type of myositis is further divided into Eosinophilic myositis, which often affects German Shepherds, Labradors and Golden Retrievers, and Doberman Pinschers, and Atrophic myositis that affects mainly long-nosed breeds. 

Extra-ocular muscle myositis – Affects the muscles involved in eyeball movement.

Polymyositis – Describes a general myositis. Is believed to be caused by an infectious organism, sometimes Ehrlichia canis, a bacterium often contracted from a brown deer tick. Lesions are found on the esophagus, forelimb muscles and masticatory muscles.

Dermatomyositis – Considered a hereditary disease that affects Shetland Sheepdogs, Australian Cattle Dogs, and other rough coated breeds. Skin lesions develop along with muscle atrophy.

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Causes of Myositis in Dogs

There are a many conditions that can cause myositis. These include:

  • Parasitic infection, such as from Toxoplasma gondii parasite
  • Bacterial infection, such as from Ehrlichia canis
  • Viral infection 
  • Immune-mediated response causing an attack against the muscle
  • Systemic lupus erythematosus
  • Reaction from drugs or toxins, such as penicillamines 
  • Cancer
  • Genetic disposition
  • Trauma
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Diagnosis of Myositis in Dogs

To come to a diagnosis, a complete physical, neurological, and oral exam is conducted, depending on the muscles that seem to be affected. Relate any history or evidence of trauma, as it can often be a cause of the myositis.

A muscle tissue sample is generally examined to look for inflammatory cells, an indicator of myositis. Masticatory muscle myositis can be directly diagnosed through a blood test that measures the level of antibodies; a 2M antibody test, and electromyography, which can highlight any abnormal electrical activity in muscles that are affected. Other tests can be performed to rule out infections or cancer, namely blood tests, and X-rays and ultrasounds of the chest and abdomen.

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Treatment of Myositis in Dogs

Once a positive diagnosis of myositis is reached, treatment attempts to counteract the immune system activity against the muscles by using immunosuppressive medications to return the system to normal. High doses of steroids, such as prednisolone, may be prescribed, as well as immunomodulators like cyclosporine, cyclophosphamide, cytarabine, azathioprine, or mycophenolate.

When the myositis is controlled, doses are decreased slowly in the hopes there is not a relapse. The goal is to eliminate all drugs, but generally a low dose of medication is continually needed to keep the symptoms from returning.

The side effects of immunosuppressive drugs can include the increased risk of infection, vomiting, diarrhea, anorexia, liver disease, bone marrow suppression, and pancreatitis. Corticosteroids can cause the muscles to atrophy, even if the dog is improving, and may not be prescribed if that is a concern.

If the underlying cause of the myositis is discovered and treated successfully, medication may be withdrawn completely. If cancer or infection is found to be the cause of the myositis, therapy is aimed to treat these conditions. Treatment for toxoplasmosis includes oral antibiotics and antiprotozoal medications over several weeks.

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Worried about the cost of Myositis treatment?

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Recovery of Myositis in Dogs

It may take many weeks to see signs of recovery and the prognosis is fair. Dogs with masticatory muscle myositis may have severe attacks for several weeks that then subside for weeks to years, and can be controlled with corticosteroids.

You may also be prescribed medications for other types of myositis to administer to your dog at home. During treatment, your veterinarian will need to monitor your dog’s progress, as well as ensure there aren’t any unwanted side effects. Be sure to notify your veterinarian if you notice any signs of these.

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Myositis Average Cost

From 382 quotes ranging from $1,000 - $3,000

Average Cost

$1,500

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Myositis Questions and Advice from Veterinary Professionals

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French Bulldog

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Two Years

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8 found helpful

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8 found helpful

Has Symptoms

Shaking

What levels in blood tests can indicate Myositis? Our French bulldog just tested with very very high ATL levels but that is the only level that is high.

July 14, 2020

Owner

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Dr. Michele K. DVM

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8 Recommendations

Thank you for your question. Myositis is typically diagnosed by muscle biopsy, and there are no reliable indicators on labwork. I"m not sure what ATL is an acronym for or if that was a typo, but if her ALT levels are very very high, that is an indicator of liver damage. We always analyze lab values as a whole picture, not just one enzyme, and take into consideration the physical examination of the dog as well. If you are having questions about what is going on with your dog, it would be best to ask your veterinarian, as they know what is going on with him/her and have access to the whole clinical picture. I hope that all goes well with your dog!

July 24, 2020

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Skana

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terrier

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17 Years

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4 found helpful

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4 found helpful

Has Symptoms

Muscle Atrophy

The side of my 17 year old terrier mix swelled up, as if she had been bitten by a bee. This has happened before, so we didn't think much of it. After about 24 hours it came down, but when it did, that side of her face was sunken in, as if she had myositis. It seems to be getting worse. She can open her mouth just fine and doesn't seem to be in pain, but why would one side of her face now lack muscle tone? Her bone is sticking out on that side.

July 26, 2018

Skana's Owner

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4 Recommendations

I’m not sure what would have cause the swelling and sudden loss of muscle in such a short period of time, muscle atrophy takes longer than 24 hours to occur; given Skana’s age, this would be something to discuss with your Veterinarian after an examination as they may find other indicators which may help to narrow in on a cause. Regards Dr Callum Turner DVM

July 26, 2018

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Myositis Average Cost

From 382 quotes ranging from $1,000 - $3,000

Average Cost

$1,500

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