Myopathies

Home » Myopathies » Overview, Incidence and Prevalence

Overview

Myopathies are diseases that affect muscles connected to bones (called skeletal muscles), such as the biceps in the upper arm and the quadriceps in the thigh. Myopathies can be caused by inherited genetic defects (e.g., 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, such as the muscular dystrophies, develop at an 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 voluntary movements (e.g., walking, reaching, talking) possible.

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 shrinkage (atrophy). 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.

Myopathies Resources

	Join Our Myopathies Forum Do you have a question, want to share medical advice, or just need to discuss your situation with someone else having a similar experience? The healthchannels forum is a resource for everyone to share and discuss their health and medical needs with others.	Advertising Disclaimer
	Living with...Share your story Do you have a personal health story that you would like to share with others? As a source of free patient education, our goal is to provide our users with trustworthy information and support from others. That's why we've started our "Living with..." sections.
	Our "Living With..." support pages are a place to share experiences about living with a certain condition, disease, disorder, or illness and for loved ones of those dealing with health-related issues. Many people, especially when newly diagnosed, find comfort in knowing that others are having a similar experience. Help others by sharing your story. View stories already submitted.
	Stay Updated Sign up for our newsletter and receive important updates on the medical conditions that are most important to you.
Advertising Disclaimer To quickly access health information from your website's browser, download Healthcommunities.com's healthchannels toolbar.