Hormonal effect on the inner ear : two endocrine syndromes

Abstract

Hearing loss is a major problem in our society with more than 5 % of the population world-wide suffering from disabling hearing loss according to the WHO. There are many endocrine syndromes associated with hearing loss. In both Turner syndrome and Pendred syndrome hearing loss is a prominent feature often leading to a need for hearing rehabilitation with hearing aids or cochlear implants. Hormonal treatment might also affect the inner ear directly and studies have shown a negative effect on hearing by progesterone treatment.

The overall aim of this thesis is to enlighten the close connection between hearing and endocrinology both directly via hormonal effects on the inner ear and indirectly by which endocrine syndromes have an impact on both hearing and endocrine target organs.

Studies I and II explore the audiological features in young women with Turner syndrome and the effect of hormonal treatment. Sensorineural hearing loss is common with high-frequency hearing loss and mid-frequency dip being the configurations most often seen. The mild to severe hearing loss concentrated to the high- and mid-frequencies leads to reduced speech perception which leads to the necessity of hearing rehabilitation with hearing aids. No effect on hearing by the hormone replacement therapy with estrogen was seen but a negative effect on high-frequency hearing, attributed to the growth hormone treatment, was found.

Study III investigates the presence of progesterone receptors in the inner ear which could explain a direct negative effect on hearing by progesterone containing hormone replacement therapy. No nuclear progesterone receptors were found according to the results of the immunohistochemistry, in rat and human, and by PCR and Western blot in rat. Therefore, direct nuclear effect seems unlikely.

Study IV investigates the natural hearing history and outcome after cochlear implantation in children with severe hearing loss due to Pendred syndrome or DFNB4 having LVAS and/or IP2-malformation. A severe to profound hearing loss is seen, often with an early onset, but progressive hearing loss is not rare. The speech and language tests show low results in expressive vocabulary and pragmatic skills but normal results in receptive vocabulary. Additional symptoms are vertigo, fluctuating hearing, motor problems, concentration deficits and sleeping disturbances.

In conclusion, hearing impairment is common and linked to several endocrine syndromes including Turner syndrome and Pendred syndrome. In both syndromes the hormonal and genetic impact can lead to severe hearing impairment though the risk for congenital severe hearing loss is present only in Pendred syndrome. An early rehabilitation with hearing aids or cochlear implants in regard to the hearing deficit is necessary to prevent social isolation and to ensure speech development and speech perception. Hormonal treatment might interfere with hearing but no direct nuclear effect of progesterone on the inner ear was found.