Mitochondrial myopathy: A group of neuromuscular diseases caused by damage to the mitochondria, energy-producing structures in cells that serve as power plants. Nerve and muscle cells require a great deal of energy and are particularly impaired by mitochondrial dysfunction.
Some of the more common mitochondrial myopathies include the Kearns-Sayre syndrome, myoclonic epilepsy with ragged-red fibers, and the MELAS syndrome of mitochondrial encephalomyopathy with lactic acidosis and stroke-like episodes.
The onset of most mitochondrial myopathies is before the age of 20. They often begin with muscle weakness. During physical activity, muscles may become easily fatigued or weak. Muscle cramping is rare, but may occur.
Aside from muscle weakness and exercise intolerance, the symptoms of mitochondrial myopathy may include nausea, vomiting, headache, seizures, stroke-like episodes, and dementia; droopy eyelids, limited mobility of the eyes, blindness, and deafness; heart failure and heart rhythm disturbances (arrhythmias); and movement disorders.
There is no specific treatment for mitochondrial myopathy. However, physical therapy can extend the range of movement of muscles and improve dexterity. Vitamins such as riboflavin, coenzyme Q, and carnitine (an amino acid) may provide some subjective improvement in fatigue and energy levels in some patients.