Overview of Myopathies in Dogs and Cats

Myopathies are a diverse group of diseases that affect the skeletal muscles.

Clinical signs of myopathies in dogs and cats typically include weakness with intact sensory function (nociception and proprioception), muscular atrophy, and muscle pain (myalgia). With some myopathies, however, muscular hypertrophy is more typical, and myalgia may be absent.

Diagnosing myopathies can be challenging, as it can be difficult to discern a myopathy from a neuropathy or neuromuscular junction disorder. Common diagnostic testing for myopathies includes serum CK activity measurement and electrodiagnostics, such as electromyographic studies. Muscle and nerve biopsies can be very helpful. A variety of special histochemical stains and reactions are available to help identify specific muscular disorders. Genetic testing is available for some myopathies.

The most common myopathies observed in dogs and cats can be grouped into five general types:

• degenerative or developmental

• metabolic

• inflammatory (immune-mediated and infectious)

• ischemic

• traumatic

Degenerative and developmental myopathies include the following:

• centronuclear myopathies

• cricopharyngeal achalasia

• exercise intolerance and exercise-induced collapse in dogs

• fibrotic myopathy

• muscular dystrophies

• myositis ossificans

• myotonia congenita

Metabolic myopathies include the following:

• exertional myopathy

• feline hypokalemic polymyopathy

• hyperadrenocorticoid (Cushing) myopathy

• malignant hyperthermia

Inflammatory myopathies (immune-mediated and infectious) include the following:

• extraocular myositis

• infectious myositis

• masticatory myositis

• polymyositis (autoimmune)

Ischemic myopathy is secondary to arterial thromboembolism in cats and is not a primary disease.

Traumatic myopathies include the following:

• coccygeal muscle injury

• iliopsoas muscle injury

• infraspinatus contracture

• quadriceps contracture