Central and peripheral nervous system conduction in mitochondrial myopathy with chronic progressive external ophthalmoplegia.

Involvement of the peripheral and central nervous systems in mitochondrial myopathy with chronic progressive external ophthalmoplegia (CPEO) has been demonstrated clinically and electrophysiologically. Systematic electrophysiological investigations of the peripheral and central nervous systems, particularly of cortico-spinal tract function, however, are not available. We studied peripheral and central nervous system involvement in 28 patients with histologically and biochemically proven mitochondrial CPEO by motor and sensory nerve conduction tests, by somatosensory, auditory and visual evoked potentials and, for the first time, by transcranial magnetic stimulation. Nervous system involvement could be demonstrated in 24 patients, affecting the peripheral and central nervous systems in 18 and 10 patients, respectively. Evidence of cortico-spinal tract involvement was found in 4 patients, which was clinically expected in only 2. Therefore, dysfunction of the cortico-spinal tract in mitochondrial CPEO may occur more frequently than so far assumed. Generally, electrophysiological tests serve as valuable supplements to clinical examination in patients with mitochondrial CPEO and may be especially helpful in therapeutic studies, i.e., coenzyme Q administration.