Myopathy

Myopathy refers to diseases that affect skeletal muscles (muscles that connect to your bones). These diseases attack muscle fibers, making your muscles weak.

Causes #

• Having a family history of myopathy. This increases the likelihood you might inherit an abnormal gene that causes muscle disease.

• Being designated male at birth (DMAB). Some myopathies are carried on the X chromosome, and actually affect more men than women. Other inherited forms of myopathy carried on other chromosomes affect all sexes equally.

• Having an autoimmune, metabolic or endocrine disorder.

• Being exposed to certain medications or toxins (see toxic myopathy below for a list of some of these medications).

Symptoms #

• Muscle weakness, most commonly of your upper arms and shoulders and thighs (more common and more severe).

• Muscle cramps, stiffness and spasms.

• Fatigue with exertion.

• Lack of energy.

Diagnosis #

• Blood tests - Muscle enzymes such as creatine kinase (CK) or aldolase may be elevated in certain myopathies as a result of the breakdown of muscle fibers.

• Electrolyte levels such as sodium, magnesium, potassium, calcium and phosphorus.

• Autoimmune disease testing such as antinuclear antibodies (ANA), rheumatoid factor, sedimentation rate and c-reactive protein.

• Endocrine testing such as thyroid hormone.

• Electromyography (EMG and nerve conduction studies), including testing the electrical conduction of your nerves and needle examination of your muscles to assess the type and degree of muscle damage.

• Magnetic resonance imaging (MRI) of your muscles.

• Genetic tests.

• Muscle biopsy, in which your healthcare provider surgically removes a small piece of muscle tissue for testing.

Treatment #

Inflammatory and autoimmune-related myopathies #

The goal of treatment is to decrease inflammation and your body’s autoimmune response. These myopathies are often treated with:

• Immunomodulatory/immunosuppressant drugs such as methotrexate, cyclosporine, tacrolimus, azathioprine, mycophenolate, rituximab and intravenous (IVIg) or subcutaneous (SubQIg) immunoglobulin.

• Corticosteroids such as prednisone or methylprednisolone.

Inherited and genetic myopathies #

• Most inherited and genetic myopathies don’t have a specific treatment or cure.

• Management is largely based on symptom control and different forms of therapy.

• There are multiple ongoing clinical trials in various areas of research looking at treatments and gene therapy.

• Duchenne muscular dystrophy and Pompe disease are disorders that can be treated with specific medication.

Other acquired myopathies #

• Healthcare providers manage acquired myopathies including endocrine, toxic and infectious myopathies by treating the underlying disease causing the myopathy.

• Toxin-related myopathies are treated by stopping the offending agent (alcohol or toluene, for example) or medication (statins, for example).

• Muscle symptoms that result from infections caused by bacteria, viruses or other infectious organisms are improved by treating the infection directly with antibiotics.