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. Inflammation can develop into cancer over time, and 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.
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, Labrador 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 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.
Recovery of Myositis in Dogs
It may take many weeks to see signs of recovery, but the prognosis is fair. Dogs with masticatory muscle myositis may have severe attacks for 3 weeks that 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.
Myositis Questions and Advice from Veterinary Professionals
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My left side of my Australian Shepherd's head was smashed. About 3 weeks later, the same side started "caving in." The vet seems to think it's muscle loss due to nerve damage. He started him on 20 mg of prednisone 2 times and day and then tapering to once a day for 10 days. Is this still considered MMM? Is there anything else we can do?
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My dog was diagnosed at 1 yr old to have Immune-mediated polymyositis. He was fine until 1 yr of age. He is 5 yrs old now. We have been able to keep his CK level down using prednisone but we cannot get him off of it. As soon as we wean him off, his lameness in his back legs comes back. He also has a hard time swallowing/drinking. The neurologist said he also has a problem with his phalangeal muscle. Most likely also due to the myocytes. I worry about him being on prednisone for his whole life. Although it is a very small amount (5mg daily for a 100lb dog) Is that much prednisone going to hurt him? Thank you
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My 2.5 year old American Bulldog, Chuck Norris was just recently diagnosed with MMM after confirmation with the 2M blood test from UCSD. We just started prednisone, and are seeing a good response from it. My question is that now he has been diagnosed, will he be prone to relapses of MMM? And if so, how do dogs fare with relapses?
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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 ?
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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.
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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!
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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
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My dog has been diagnosed with mmm he has been on a high dose of prednisolone for about a week it is only in his head at the moment but he has lost 2 kilos in 2 weeks and I am worried about that is that normal and how long does it take for the steroids to start to kick in
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Normally in cases of masticatory muscle myositis you would expect to see some improvement between one to two weeks and once improvement is seen, the dose of corticosteroids may be reduced. Recurrence is common and long term treatment may be required. Whilst corticosteroids are the main treatment, I’ve read about some success with acupuncture as well. Regards Dr Callum Turner DVM
Hi there my chocolate lab who is 7 has just been diagnosed with mmm 4 days ago. He was put on steroids which worked immediately but he's been very sick with them and has a very bad stomach so the vet had to give him a steroid injection instead of the tablets. He isn't in any pain but he's really not himself and we are very worried about him. How is Your dog Flynn now?
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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.
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Hello, our Lab "Porter" will be 14 yrs old in February (2018), and has been diagnosed with MMM for the past year. He has lost muscle around his right eye, and is blind on that side now. He has been eating his regular food, but I have noticed that his drinking is more restricted - it appears that he cannot open up all the way. I know that is the progression of this disease, but is there a timeline of how quick this progresses to the point where the jaw is totally locked?
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I am very concerned about treating my dog with this condition...he’s got diabetes. The drugs are strong and I’m not sure I want him to go through any more pain etc.
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how likely is it a dog can be diagnosed with mmm and die 4 months later? How does this cause "hemorage" from her nose? She had phemonia. Not sure if either one of this could cause "hemorage".'
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Hi my golden retriever has been diagnosed with muscle myositis and he's blind from one eye, he seems to have lost the muscle tissue on the left side of his head and his bext is tilted to the side. He cannot go up/downstairs anymore. He is not eating or drinking water. Any hope he may go back to normal with medication?
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Myositis may affect one muscle, one group of muscles or all muscles; treatment is usually aimed at calming down the immune system (corticosteroids and other immune system suppressants). Effective treatment may result in a worsening of symptoms initially which may scare pet owners. Options for Chucky should be discussed with your Veterinarian as no too cases are the same; prognosis is usually fair for this type of condition but varies case to case. Regards Dr Callum Turner DVM
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