The myopathies are neuromuscular disorders in which the primary symptom is muscle weakness due to dysfunction of muscle fiber. Other symptoms of myopathy can include include muscle cramps, stiffness, and spasm.
Myopathies can be inherited (such as the muscular dystrophies) or acquired (such as common muscle cramps). Myopathies are grouped as follows:
congenital myopathies: characterized by developmental delays in motor skills; skeletal and facial abnormalities are occasionally evident at birth
muscular dystrophies: characterized by progressive weakness in voluntary muscles; sometimes evident at birth
mitochondrial myopathies: caused by genetic abnormalities in mitochondria, cellular structures that control energy; include Kearns-Sayre syndrome, MELAS and MERRF
glycogen storage diseases of muscle: caused by mutations in genes controlling enzymes that metabolize glycogen and glucose (blood sugar); include Pompe’s, Andersen’s and Cori’s diseases
myoglobinurias: caused by disorders in the metabolism of a fuel (myoglobin) necessary for muscle work; include McArdle, Tarui, and DiMauro diseases
dermatomyositis: an inflammatory myopathy of skin and muscle
myositis ossificans: characterized by bone growing in muscle tissue
familial periodic paralysis: characterized by episodes of weakness in the arms and legs
polymyositis, inclusion body myositis, and related myopathies: inflammatory myopathies of skeletal muscle
neuromyotonia: characterized by alternating episodes of twitching and stiffness; and
stiff-man syndrome: characterized by episodes of rigidity and reflex spasms
common muscle cramps and stiffness, and
tetany: characterized by prolonged spasms of the arms and legs.
The prognosis for individuals with a myopathy varies. Some individuals have a normal life span and little or no disability. For others, however, the disorder may be progressive, severely disabling, life-threatening, or fatal.
Treatments for the myopathies depend on the disease or condition and specific causes. Supportive and symptomatic treatment may be the only treatment available or necessary for some disorders. Treatment for other disorders may include drug therapy, such as immunosuppressives, physical therapy, bracing to support weakened muscles, and surgery.