Audiological evaluation in Chinese patients with mitochondrial encephalomyopathies

Hearing impairment has been reported to be common in patients with mitochondrial disorders, a group of diseases characterized by pleiomorphic clinical manifestations due to defects in oxidative phosphorylation of mitochondria. This study aimed to investigate the audiological characteristics in a large cohort of patients with mitochondrial disease.

Comprehensive audiological evaluations, including pure tone audiometry, tympanometry, speech audiometry, otoacoustic emissions, electrocochleography and auditory brainstem evoked potentials, were performed in 73 Chinese patients with mitochondrial encephalomyopathy and with confirmed mitochondrial DNA (mtDNA) defects.

Among the patients, 71% had hearing impairment. However, the incidence rate and severity of hearing impairment were much less in the chronic progressive external ophthalmoplegia (CPEO) subtype than in the mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes (MELAS), myoclonic epilepsy with ragged red fibers (MERRF) and Kearns-Sayre syndrome (KSS) subtypes. While most of our patients had a predominantly cochlea origin for the hearing deficit, five patients had an auditory neuropathy spectrum disorder and three patients had impairment of both cochlea and auditory cortex.

Various portions of the auditory system could be involved in patients with mitochondrial diseases, including cochlea, auditory nerve, auditory pathway and cortex. Hearing loss was more associated with multisystem involvement. Genotype, mutant load of mtDNA and other unknown factors could contribute to heterogeneity of hearing impairment in mitochondrial disease.