Diabetes and hearing dysfunction: under-recognized complication of diabetes?

Prevalence of diabetes, especially type 2 diabetes, has reached an epidemic level. In 2012, about 371 million people worldwide are estimated to have diabetes.[1] Diabetes may lead to development of several complications, of which retinopathy, nephropathy, peripheral neuropathy, and accelerated atherosclerosis have been most widely studied. However, diabetes may also lead to other important consequences. It has been demonstrated that prevalence of hearing impairment in diabetic patients, measured by a pure-tone audiometry, is roughly doubled as compared with that in a general population.[2] Moreover, the clinical importance of audiological complications of diabetes mellitus remains underestimated and undervalued.

Sense of hearing, together with sense of sight, are the most important tools of social communication. Dysfunction of any of these senses has a significant impact on the quality of life of the affected person. Disturbances of auditory organ function were noted in both type 1 and 2 diabetic patients. The disturbances can be measured by a pure-tone audiometry, which reflects the function of the auditory organ as a whole, by an otoacoustic emissions evaluation, which is used to determine the status of the cochlear micromechanics, especially the function of the outer hair cells and by an auditory brainstem response audiometry, which is a neurological test used to determine the function of the retrocochlear part of the acoustic pathway up to the brainstem level. Abnormalities in these evaluations were seen in young patients with type 1 diabetes as well as in middle-aged patients with type 2 diabetes, with a relatively short duration of the disease. They demonstrated higher hearing thresholds at middle and high frequencies (3–12 kHz and 4–8 kHz, respectively) as well as longer wave V and interpeak I-V latencies in the auditory brainstem responses evaluation in comparison with non-diabetic subjects.[34] In addition, in type 1 diabetic subjects, lower amplitude of otoacoustic emissions were seen, which may indicate impaired function of the cochlea.[3] Thus, hearing organ impairment (diabetic “otopathy”) may be also considered as an another diabetic complication.

The study by Gupta et al.[5] demonstrated significant differences between diabetic and non-diabetic subjects regarding waves III and V latencies, interpeaks III–V and I–V latencies bilaterally, and wave IV latency unilaterally (in the right ear). These abnormalities showed correlation with fasting blood glucose levels and the duration of diabetes. This study confirmed the existence of early central diabetic neuropathy that can precede other clinical manifestations of that consequence of diabetes.

Findings of these, together with findings of other studies, indicate the need for early screening of the auditory organ involvement in diabetic subjects, similar to that in the eye fundus examination, microalbuminuria, or touch sensation assessment. Otherwise, they might not hear what they are missing.