Early subclinical cochlear dysfunction in myotonic dystrophy type 1.

BACKGROUND: Myotonic dystrophy type 1 (DM1) is an autosomal-dominant inherited disorder clinically characterized by variable systemic manifestations. Among clinical features of the disease, 'precocious presbyacusis' has been previously reported. The underlying mechanism of this auditory impairment remains still poorly understood. Hearing is an active process located in the cochlea, where the outer hair cells (OHCs) play an important role in sound perception through a 'contractile' like movement resembling skeletal muscle fibers dynamics. OHCs status has not yet been investigated in DM1 patients. OHCs integrity can be assessed by measuring transient-evoked otoacoustic emissions (TEOAE), a non-invasive, repeatable, and objective quantitative tool. METHODS: We recruited 25 patients with a genetically confirmed diagnosis of DM1, and 28 age-matched control subjects. All of them underwent a routine audiological evaluation and TEOAE recordings. RESULTS: We detected a high prevalence of sensorineural high-frequency hearing loss (HFHL) in DM1 patients, significantly different if compared to control subjects. Interestingly, the accurate analysis of DM1 recorded data showed a marked impairment of TEOAE both in HFHL+ and unexpectedly in HFHL- group. Cochlear dysfunction was restricted to frequencies above 2000 Hz in the HFHL- group, but it extended to 1000 Hz in HFHL+ DM1 patients. CONCLUSIONS:   Our study indicates that cochlear impairment in DM1 is present, even in patients without evidence of hearing loss at a standard audiometric analysis. Hence, in the current clinical practice, an assessment of cochlear function by TEOAE recording may be useful in DM1 patients to identify precocious signs of cochlear dysfunction.