Myositis in Dogs: Causes, Symptoms and Treatment

Myositis refers to a set of disorders that alter the muscle membrane, with the consequent loss of active motor functionalities.
Myositis in Dogs: Causes, Symptoms and Treatment

Last update: 02 May, 2022

Although the term “myositis in dogs” may lead you to think of a single disease, in reality, it encompasses a series of muscular pathologies with an etiology determined by the immune system. However, we still need to expand our knowledge regarding the origin and effects of the disease.

If you delve into the origin of this word, it’s actually the union of two terms: “mio” which means muscle and “itis” which means inflammation. This clearly describes the main symptom of the disease, which is to cause muscle inflammation. But this isn’t all.

What is myositis in dogs?

Myositis refers to a set of disorders that alter the muscle membrane, with the consequent loss of active motor functionalities. Because of this, the muscles that maintain 100% of their functions must take over the work performed by the affected ones.

This means an overload for these muscles, which means greater fatigue when exercising. These myositis are subdivided into two large groups:

  • Immune-mediated
  • Infectious

Types of myositis in dogs

A dog.

Currently, a series of muscular pathologies incorporated within the term myositis have been determined. Types will be mentioned below, in particular those that are immune-mediated.

Immune-mediated myositis in dogs

Some examples of immune-mediated myositis, i.e. those involving the immune system, can be found explained below.


In this category of myositis, degenerated and destroyed muscle tissue occurs in a generalized form. Compared to other forms of the disease, in this situation, the muscles affected are usually those located in the body’s extremities.

For this reason, a quick way to detect the disease is the loss of strength observed in the dog when exercising. In extreme cases, muscle atrophy is perfectly observable on a physical level in the animal.

Myositis in the masticatory muscles

This type of myositis shows a very specific form of the disease. It’s determined as an autoimmune disorder in which the body itself produces a cross-reaction. It generates antibodies directed against an infectious agent, but ends up attacking the M2 muscle fibers of the muscles related to mastication and are:

  • Temporal
  • Digastric
  • Pterygoid
  • Masseter

This attack causes the destruction of the tissue that makes up the aforementioned muscles. In addition, its terminology varies, as it isn’t only known as myositis in the masticatory muscles, but also as eosinophilic myositis or atrophic myositis. However, it seems that these terms are associated with the acute and chronic phase of the disease.

Causes of myositis in dogs

When looking into myositis in dogs you can note a number of causes such as age, hypothermia, trauma, or parasitosis.


This is one of the most striking factors of this disease, as it appears when they’re between 2 and 3 years old. However, sometimes it can also appear at 4 months of age. In addition, it’s more frequent in large breeds of dogs, such as Golden Retrievers.


Another possible cause is exposure to a climate with low temperatures. If the dog hasn’t adapted and isn’t prepared to endure these temperatures, they may develop myositis. The muscles will begin to show difficulties in movement due to the cold, and symptoms such as inflammation will be observed.


Some parasites belonging to the Leishmania or Toxoplasma genera, are responsible for diseases such as toxoplasmosis or Leishmaniasis. In the list of symptoms of each pathology, you’ll probably find some type of the myositis described above.


This is the most common cause of the onset of myositis, along with age. A blow or strong physical activity can lead to a hematoma or muscle rupture and, in turn, to this condition.

Symptoms of myositis in dogs

Undoubtedly, difficulty in movement will be one of the first symptoms observed in the animal. This will worsen as the day progresses and, possibly, the dogs will groan in pain when they try to move.

The areas of the body where the appearance of myositis is first observed are the pelvic and shoulder regions. In addition, you should also be on the lookout for other symptoms such as:

  • Movement difficulties – changes in its normal position on the back or difficulties to support one or more legs
  • Fever
  • Blood in the urine
  • A lack of appetite

Within each variation, one will observe symptoms of their own such as swelling of the facial muscles or difficulty in chewing. This occurs in the case of myositis in the masticatory muscles.

Unfortunately, if the disease progresses to the chronic stage, other symptoms are perceived. Above all, the visible lump or mass on the head is one of the most recognized by specialists.

Treatment of myositis in dogs

A Dalmatian.

It appears that in most of the different variants of the disease, the treatment to be followed includes the administration of immunosuppressants, such as corticosteroids. The duration of the treatment will be decided by the specialist, but it’s usually maintained for 8 to 12 months and the dose is reduced as the symptoms remit.

However, each variant will need to complete the pharmacological treatment with another series of guidelines. For example, in poliomyelitis, a period of rehabilitation and physiotherapy is essential in order to improve the dog’s response time and accelerate recovery.

In myositis of the masticatory muscles, if the diagnosis and subsequent treatment occur during the acute phase of the pathology, the prognosis is good. However, if it occurs in the chronic phase, then there is more chance of complications occurring.

In short, myositis includes different pathologies that share a common pathogenesis: they inflame the muscles and affect their functionality. If you have observed some of the symptoms described above, it’s advisable to consult your veterinarian to find out the possible causes and they’ll guide you as to what to do.

All cited sources were thoroughly reviewed by our team to ensure their quality, reliability, currency, and validity. The bibliography of this article was considered reliable and of academic or scientific accuracy.

This text is provided for informational purposes only and does not replace consultation with a professional. If in doubt, consult your specialist.