Progressive sensorineural hearing loss in children with mitochondrial encephalomyopathies

Objective: Mitochondrial disorders are responsible for a variety of neurolo gical syndromes. Specific mitochondrial DNA mutations have been identified recently in some of these rare disorders. Clinical symptoms may occur in di fferent organs to various extent; often they are associated with progressiv e hearing loss. The aims of this study were to determine incidence, onset, and characteristics of hearing loss in children with mitochondrial encephal omyopathies and to investigate a possible correlation between the degree of hearing loss and neurological symptoms. In addition, we investigated the p rognostic value of hearing loss as a predictor of the disease. Study Design : From August 1992 to September 1998, 29 patients ranging in age from 5 to 23 years (mean years) were studied. These children were hospitalized for di agnostic purposes in the neuropediatric department. Methods: The mitochondr ial disorder was diagnosed by clinical and laboratory testings, including a nalysis of the mtDNA Audiological evaluation consisted of measurements of p ure-tone and speech audiometry, tympanometry, and acoustic reflex threshold testing, auditory brainstem response, and evoked as well as distortion-pro duct otoacoustic emissions. Results: A sensorineural hearing loss was ident ified in 12 children. Three of these were diagnosed as having classic Kearn s-Sayre syndrome; five as having multisystem KSS; two as having the syndrom e of mitochondrial myopathy, encephalopathy, lactic acidosis, and stroke-li ke episodes (MELAS); one as having KSS-MELAS overlap syndrome; and one as h aving Friedreich ataxia. Longitudinal testing was performed in seven childr en, and in all of them a progression of the hearing loss could be demonstra ted. Audiological test results in all 12 children suggested cochlear as wel l as retrocochlear origin of the hearing loss presenting independently from the severity of hearing impairment. No correlation between the characteris tics and degrees of hearing loss and the number and severity of clinical ne urological symptoms could be found. Conclusions: The present study demonstr ated a high incidence (42%) of sensorineural hearing loss in children with mitochondrial encephalomyopathies. The progressive nature of the hearing im pairment was confirmed by a significant correlation between the duration in years and severity of hearing loss in the children. The hearing loss does not have a prognostic value for the progression of the disorder. Based on o ur findings, we recommend regular audiometric examinations in patients with mitochondrial disorders.