Myopathy is a disorder of the skeletal muscles. Muscle disorders arise from abnormalities that affect the muscle’s structure or metabolism, and have a variety of causes. Some are inherited (genetic) while others are acquired (not inherited). Inherited myopathies have a genetic basis and typically appear in childhood, but first symptoms can also appear in adulthood.
Below are examples of inherited (genetic) muscle diseases:
- Muscular dystrophies including Duchenne/Becker muscular dystrophy, limb girdle muscular dystrophy, facioscapulohumeral muscular dystrophy, myotonic dystrophy, distal myopathy, etc
- Congenital myopathies such as central nuclear myopathy, central core myopathy, nemaline myopathy
- Metabolic myopathies including glycogen storage myopathy, lipid storage myopathy, and mitochondrial myopathy.
- Myopathies may be related to channelopathies such as periodic paralysis, or non-dystrophic myotonic disorders.
Below are examples of acquired muscle diseases:
- Inflammatory myopathies, which may be associated with polymyositis, dermatomyositis, inclusion body myositis, immune-mediated necrotizing myopathy.
- Toxic myopathies, which might be caused by:
- myotoxic medications: cholesterol-lowering agents such as statins, colchicine, Plaquenil, steroids, anti-retroviral drugs, Amiodarone, etc.
- toxins such as alcohol or toluene
- Myopathies, which can be related to infectious diseases such as HIV, parasitic and bacterial pyomyositis.
Myopathies may be due to systemic diseases including thyroid disorders, lupus, rheumatoid arthritis, Sjogren’s syndrome, sarcoidosis, amyloidosis, or critical illness.
If you have a muscle disease, you may experience weakness, most likely in the thighs and upper arms. It can become difficult to climb stairs, rise from a chair, or lift your arms above your head. Cramping, stiffness, and soreness can also occur. Some myopathies can affect muscles in the hands or feet, or facial and eye muscles. In some cases, the problem can affect the heart and breathing muscles.
Inflammatory myopathies can occur when the body’s immune system causes inflammation in the muscle. In certain instances, they can also be associated with an underlying malignancy. Toxic myopathies can be due to medications or environmental toxins. Infectious myopathies can be caused by viruses, bacteria, or parasites. Muscles can also be affected with systemic illnesses, including connective tissue diseases, endocrinopathies, and others as listed above.
Treatment depends on your precise diagnosis. If we suspect an acquired myopathy, such as inflammatory myopathy, your physician may recommend a muscle biopsy to evaluate the structure of the muscle. We typically treat inflammatory myopathy withoral immunosuppressant medications and occasionally chemotherapeutic agents. We recommend genetic testing and counseling if the condition is inherited (genetic).
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