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Pinky S. Tiwari, M.D., P.A.
Diplomate, American Board of Neurology
Diplomate, American Board of Electrodiagnostic Medicine
St. Luke’s Medical Tower
6624 Fannin, Suite 2190
Houston, TX 77030
Telephone: (713) 790 – 1775
www.texasneuro.com
Fax: (713) 790 – 1605
What is Myopathy?
Overview
Diseases that affect skeletal muscle—muscles connected to bones, like the biceps in the upper arm and
quadriceps in the thigh—are called "myopathies." Myopathies can be caused by many types of conditions,
including inherited genetic defects (e.g., the muscular dystrophies), and endocrine, inflammatory (e.g.,
polymyositis), and metabolic disorders.
Nearly all of the myopathies produce weakening and atrophy of skeletal muscles, especially those closest to
the center of the body (called the proximal muscles), such as the thigh and shoulder muscles. Muscles furthest
from the center of the body (called the distal muscles), such as those in the hands and feet, are generally less
affected.
Some myopathies, like the muscular dystrophies, develop at a very early age; others develop later in life.
Some worsen over time and do not respond well to treatment; others are treatable and remain stable. Many
times a myopathy is simply labeled "nonspecific muscle myopathy" because there are few treatments available
that address the root cause of disease.
Skeletal Muscle
Every time the body moves, a skeletal muscle contracts. Skeletal muscles are attached to parts of the skeleton
and make possible voluntary movement like walking, reaching, and talking.
Depending on where they are and how they function, skeletal muscles vary considerably in size and shape, but
they are all made up of bundles of fibers. Each fiber is made up of a sophisticated system of sliding filaments
that, when "told" what do by the brain via the nervous system, cause contraction and movement. The nerves
that command the muscle are called motorneurons, and the place where a motorneuron meets the muscle is
called the neuromuscular junction.
Motorneurons communicate to muscles by secreting biochemical substances. The skeletal muscles receive
that biochemical energy and transform it into the mechanical energy that causes muscles to contract and move
the human body.
When muscles are affected by disease, many changes occur that may lead to weakness, pain, and atrophy.
The muscle fibers can be destroyed or can show significant atrophy (shrinkage). In the inflammatory
myopathies, white blood cells and other blood elements may attack parts of the muscle and surrounding blood
vessels. Scar tissue may take the place of normal muscle. In some of the metabolic myopathies, abnormal
amounts of biochemical substances may accumulate in the muscles.
Incidence and Prevalence
Worldwide incidence of all inheritable myopathies is about 14%. Central core disease accounts for 16% of
cases; nemaline rod myopathy for 20%; centronuclear myopathy for 14%; and multicore myopathy for 10%.
Prevalence of muscular dystrophy is higher in males. In the United States, Duchenne and Becker MD occur in
approximately 1 in 3300 boys. Overall incidence of muscular dystrophy is about 63 per 1 million.
Worldwide incidence of inflammatory myopathies (e.g., dermatomyositis, polymyositis) is about 5–10 per
100,000 people. These disorders are more common in women.
Incidence and prevalence of endocrine and metabolic myopathies are unknown. Corticosteroid myopathy is the
most common endocrine myopathy and endocrine disorders are more common in women. Metabolic
myopathies are rare but diagnosis of these conditions is increasing in the United States.
Is there any treatment?
Treatments for myopathy vary depending on the type.
Supportive and symptomatic treatment may be the only treatment available or necessary in some cases.
Treatment for other forms may include drug therapy, such as immunosuppressives, physical therapy, bracing,
and surgery.
What research is being done?
The NINDS supports and conducts an extensive research program on neuromuscular disorders such as the
myopathies. Much of this research is aimed at increasing scientific understanding of these disorders, and
finding ways to prevent, treat, and cure them.
Organizations
National Institute of Arthritis and Musculoskeletal and Skin Diseases (NIAMS)
National Institutes of Health
Bldg. 31, Rm. 4C05
Bethesda, MD 20892-2350
[email protected]
http://www.nih.gov/niams
Tel: 301-496-8188 877-22-NIAMS (226-4267)
Muscular Dystrophy Association
3300 East Sunrise Drive
Tucson, AZ 85718-3208
[email protected]
http://www.mdausa.org/
Tel: 520-529-2000 800-572-1717
Fax: 520-529-5300