Immune-Mediated Polymyositis in Dogs

Immune-mediated polymyositis is a condition that seriously and negatively impacts a dog’s skeletal muscle. This includes leg muscles, laryngeal muscles, masticatory muscles and their pharyngeal muscles. On top of this, immune-mediated polymyositis can be a primary health disorder or it can develop as a result of dogs suffering from other immune mediated conditions which includes systemic lupus erythematosus.

Breeds Most at Risk

Studies have shown that certain breeds appear to be more predisposed to suffering from the condition than others with the following being high on the list:

• Hungarian Vizsla

It is worth noting that this disorder has been associated with another condition known as Vogt-Koyanagi-Harada syndrome which is another autoimmune disorder that seriously impacts their melanocyte antigens. Some studies have suggested that the condition can also be linked to other health issues namely the following:

• Lymphoma
• Thymoma
• Myeloid leukemia
• Bronchogenic carcinoma
• Tonsillary carcinoma
• Anaplastic round cell tumours
• Lasmacytoma

Symptoms Associated with the Disorder

Dogs suffering from the condition are usually middle-aged when any symptoms start to develop and they show the following signs of there being something wrong with them:

• A general weakness
• A stiff and stilted gait which is referred to as dysbasia
• Myalgia
• Vomiting (intermittently)
• Dysphagia
• Dysphonia
• Loss of weight
• Loss of muscle tone
• Muscle contractions
• Facial atrophy
• Tongue atrophy

Diagnosing the Problem

A vet would ideally need to know a dog's full medical history and how the onset of any symptoms first presented themselves. Dogs suspected of suffering from the condition would be thoroughly examined with vets typically recommending the following tests although taking bloods does not always prove fruitful when it comes to establishing a definitive diagnosis:

• A complete blood count
• A full blood biochemistry profile
• Several biopsies of a dog's biceps femoris (thigh muscle) or their vastus lateralis (large thigh muscle)

The vet would also want to rule out any other health disorders that might be causing the symptoms which could include the following before giving a definitive diagnosis:

• Toxoplasma gondii
• Hepatozoon americanum
• Sarcocystis neurona
• Neospora spp
• Hammondia hammondi
• Masticatory muscle myositis
• Tetanus
• Myasthenia gravis
• Duchenne muscular dystrophy
• Golden Retriever Muscular Dystrophy
• Thymoma
• Dermatomyositis

Treatment Options

A vet would typically prescribe a course of immuno-suppressants with dogs usually responding well to treatments providing any inflammation and fibrosis can be controlled, reduced or stopped altogether. Any dog that has been diagnosed and treated for immune-mediated polymyositis would need to be taken for regular health checks at the vet so their conditions can be reassessed.