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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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.
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
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.
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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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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Top
Myositis Questions and Advice from Veterinary Professionals
Doberman Pinscher
Ripley
One Year
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My pet has the following symptoms:
Mastictory Myositisis
My dog Ripley has been diagnosed with mmm. Shes on 30 mg prednisone 2 times a day . She is doing well .When can I start lowering the amount and how much do i lower it and for how long before lowering it more. Should she receive any of her yearly vaccine's ?
March 27, 2018
0 Recommendations
The link below has information on dosage and tapering of treatment but should be used as a guide; you should only reduce the dosage under your Veterinarian’s instruction as they are the prescribing Veterinarian. Also any vaccines due should be given at your Veterinarian’s discretion. Regards Dr Callum Turner DVM
www.msdvetmanual.com/musculoskeletal-system/myopathies-in-small-animals/masticatory-myositis-in-small-animals
March 27, 2018
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Husky
Allie
13 Years
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My older husky cross has always been vigorous and healthy, although she was getting a little arthritic in one shoulder. I started giving her CBD oil to which she seemed to respond really well. I ran out perhaps two weeks ago and ordered more. Then, after being off the drops for maybe a week, she started acting lethargic and less interested in eating. Monday and Tuesday she didn't eat at all and Wednesday I took her to the vet. I had noticed soreness around her ears and jaw, and my vet diagnosed MMM and started her on steroid treatment. She ate within hours of returning home and has continued to do so. My question is whether the CBD could have played any role- did the cessation of CBD trigger a flare up? Should I continue to use the drops at this point? Thank you in advance.
March 17, 2018
Answered by Dr. Michele K. DVM
0 Recommendations
Thank you for your email. Unfotunately, there hasn't been enough (or any) research to show the effects of cbd oil in dogs. Whether it would help or hurt is unknown at this point. Since she is responding to therapy, it would be best to follow your veterinarian's advice. I hope that Allie continues to do well.
March 17, 2018
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American bully
Brownie
7 Months
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My pet has the following symptoms:
Eye Bulging
Lethargy
Head Swelling
Loss Of Appetite
Hi,
My friends American Bully is 7 months and about a week ago she took him to the her local Vet Clinic because he was not acting like himself. He was not active, he seemed to have discomfort from his head every time someone will try to pet him. At the clinic the Vet told my friend that it looked like he got stung by an animal (possibly a spider) they gave him anti-inflammatory medicine for this and in a couple of days Brownie was better. After a week of that incident, Brownie started showing the same symptoms again. The swollen of his head came back , he was not opening his eyes, low or not activity at all, he is not taking any food or water. My friend rushed him to the Vet again and they ordered blood work and x-rays which both came back normal .(which was a good thing). The Vet didn't gave her a diagnosed because all the test performed so far came back positive and he said that the final thing will be to perform an MRI. He also told her that honestly it might be a neurological condition called Hydrocephalus, but that he was not sure and he didn't think it was worth to spend more money on the dog because it that was the diagnosed it didn't had a cure. We are desperate and do not know what to do. I told my friend not to give up on Brownie, I'm doing a lot of research and came across this Myositis disease that pretty much describes a lot of the symptoms that Brownie is experiencing. I also found places that will perform the MRI for a much lower cost that the place suggested by my friend's Vet ($2,500) . Please help us save Brownie and take the right direction, any help will be appreciated it!
March 9, 2018
Answered by Dr. Michele K. DVM
0 Recommendations
Thank you for your email. I'm sorry that is happening to Brownie. It might be a good idea to have a referral to a specialist, as they are people that analyze neuromuscular disease all the time. They may be able to narrow down what is happening, and give you a better idea as to any appropriate testing that may need to be done - whether it is an MRI, spinal tap, or otherwise. Your veterinarian can help you find a specialist in your area. I hope that everything goes well for Brownie.
March 9, 2018
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Australian Shepherd
RIPLEY
5 Years
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My pet has the following symptoms:
Swollen Head And Jaw, Bulged Eyes
My Aussie showed no prior symptoms of mmm until he spent the weekend with my daughter and her boyfriend. Symptoms began quickly. First he became quiet and sat alone. Next day refused to eat. Then stopped drinking. Then his head began to swell and his eyes bulged out as if he’d been in the ring with Mike Tyson!! 3 days with one vet... I was told he was dying and nothing they could do. I removed him and took him to The University of Guelph Animal Hospital. They diagnosed him with mmm.
My question is... how can I be sure it was mmm and not blunt force trauma to the head? He had secondary pain to the touch in his abdomen. Upon having an ultrasound done basically 5days after symptoms began he showed no cause for such pain.
He was put on prednisone along with two eye gel medications. One week later he made a total recovery! Drs are amazed! No sunken face. Eyes had ulcers but healed up in one weeks time as well (while on Prednisone)???
Is he a miracle dog or simply misdiagnosed after what I suspect was a major beating by the “boyfriend”
I need to KNOW as to ensure Ripley gets the proper care needed over his lifetime.
*I also read in this report trauma “CAN CAUSE” myositis?
Jodie,
Hamilton, Ontario
Feb. 26, 2018
0 Recommendations
One week recovery from masticatory muscle myositis seems quite remarkable, the diagnostic method of choice to confirm a diagnosis of masticatory muscle myositis is a biopsy of the muscle to confirm myositis. I cannot say whether the cause for the symptoms was due to trauma, inflammation, temporomandibular joint disorders, another cause or a mix of them all; you should speak more with Ontario Veterinary College to get their views based on their examination and case notes. Regards Dr Callum Turner DVM
Feb. 26, 2018
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lab
Nicki
7 Years
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My pet has the following symptoms:
Sunken Cheeks, Sunken Head
Hi. Our dog nicki has had sunken cheeks for a long time. The vet at BA field never could tell us what it was. Then her head started to sink in on top and her eyes kind of sink a bit in. I couldn't take it anymore and sent pics to to a different vet and they diagnosed her with this disease. We are going on Monday to meet and get meds. If meds work will her muscle rebuild? Or is it too late for her. I'm so angry with BA field for not catching it and with myself for not going to a different vet sooner. She eats and drinks fine. Plays with bones and doesn't act in pain. I just don't know if I can live with myself if it's too late for her.
Feb. 10, 2018
0 Recommendations
Each case is different, but you should see a response to treatment but remember that treatment is long and not to expect an overnight change. I cannot say why the original Veterinarian didn’t come to that diagnosis but hopefully Nicki can start treatment and improve. Regards Dr Callum Turner DVM
Feb. 10, 2018
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Myositis Average Cost
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Average Cost
$1,500
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