Myopathy Overview, Incidence and Prevalence of Myopathy

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), or by endocrine, inflammatory (e.g., polymyositis), and metabolic disorders.

Overview of Myopathy

Nearly all types of myopathy produce weakening and atrophy of skeletal muscles, especially those muscles closest to the center of the body (called the proximal muscles), such as the thigh and shoulder muscles. Muscles further from the center of the body (called the distal muscles), such as those in the hands and feet, are generally affected less often.

Incidence and Prevalence of Myopathy

Worldwide incidence of inheritable myopathies is about 14%. Of all inheritable myopathyies, central core disease accounts for 16% of cases; nemaline rod myopathy accounts for 20%; centronuclear myopathy accounts for 14%; and multicore myopathy accounts for 10%.

Prevalence of muscular dystrophy is higher in males. In the United States, Duchenne MD 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 type of endocrine myopathy and endocrine disorders are more common in women than in men. Metabolic myopathies are rare, but diagnosis of these conditions is increasing in the United States.

Incidence and Prevalence of Myopathy

Worldwide incidence of inheritable myopathies is about 14%. Of all inheritable myopathyies, central core disease accounts for 16% of cases; nemaline rod myopathy accounts for 20%; centronuclear myopathy accounts for 14%; and multicore myopathy accounts for 10%.

Prevalence of muscular dystrophy is higher in males. In the United States, Duchenne MD 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 type of endocrine myopathy and endocrine disorders are more common in women than in men. Metabolic myopathies are rare, but diagnosis of these conditions is increasing in the United States.