A Case of Mitochondrial Encephalopathy with Peripheral and Cortical Auditory Damage

Abstract

A 21-year-old female complained of headache and vomiting as the first neurologic symptom at 17 years of age. Mitochondrial encephalopaty, lactic acidosis and stroke-like episodes (MELAS) was diagnosed by clinical findings and muscle biopsy revealing ragged red fibers. Next year, bilateral sensorineural hearing loss was found. After a strokelike episode at age 20, she noticed the difficulty with recognition of speech and environmental sounds, but hearing level (50dBnHL) on pure tone audiometry (PTA) was not changed. These psychoacoustic deficits revealed auditory agnosia due to cortical lesions. The thresthold in ABR was consistent with that in PTA and prolongation of I-V wave was not found. EOAE response was not detected at level of 78.5dB. Brain MRI and CT showed cerebral cortical atrophy in the temporal, parietal and occipital lobes and ventricular dilatation. PET images of cerebral glucose metabolism and blood flow indicated that the areas of activity were rightlateralized in the temporal gyrus and the posterior inferior frontal region (Broca area). We concluded that hearing disturbance in this case might be caused by decrease of cochlear function and cortical auditory damage.