[Two cases of mitochondrial myopathy (focal cytochrome c oxidase deficiency), long-term follow-up on a diagnosis of ocular type myasthenia gravis].

Two patients (a 50-year-old and a 35-year-old men) with focal cytochrome c oxidase deficiency, manifesting ptosis and external ophthalmoplegia of 13 and 6 years' duration, respectively, were reported. Patient 1 (a 50-year-old male) had also slight muscular weakness of the proximal limb and neck flexor muscles. Diagnosis of myasthenia gravis had been made on the clinical findings including ptosis and external ophthalmoplegia, diurnal fluctuation of symptoms, and equivocal positive Tensilon test. However, waning phenomenon on repetitive nerve stimulation or elevation of titer of the anti-acetylcholine receptor antibody was not detected on both patients. Needle EMG showed mild myopathic changes. Finally, pathological and biochemical analyses of the biopsied muscles confirmed the diagnosis of mitochondrial myopathy (focal cytochrome c oxidase deficiency).