Mechanisms involved in hearing disorders of thyroid ontogeny: a literature review

Abstract

Endocochlear, retrocochlear and/or central origin hearing damage may be related to the absence of appropriate levels of thyroid hormone during morphogenesis and/or auditory system development. Hearing disorders related to the thyroid are not well studied, despite speculation on the pathophysiological mechanisms. The objective of this review was to characterize the main pathophysiological mechanisms of congenital hypothyroidism and to evaluate the relationship with central and peripheral hearing disorders. We conducted a literature review using the databases MedLine, LILACS, Cochrane Library, SciELO, Institute for Scientific Information (ISI), Embase, and Science Direct between July and September on 2016. We identified the studies that address hearing disorder mechanisms on the congenital hypothyroidism. Congenital hypothyroidism may have clinical and subclinical manifestations that affect the auditory system and may be a potential risk factor for hearing impairment. Hearing impairment can severely impact quality-of-life, which emphasizes the importance of monitoring and evaluating hearing during the clinical routine of these patients. Arch Endocrinol Metab. 2017;61(5):501-5

High Prevalence of Hearing Impairment in Primary Congenital Hypothyroidism

“…Delayed initiation of LT 4 supplemental therapy or inadequate therapy results in delayed psychomotor development and is associated with higher rates of HI [2]. Interestingly, in our study, there was no difference in the age at initiation of supplemental therapy between patients with HI and those with normal hearing.…”

“…The development of hearing in humans, as well as in rodents, is highly dependent on a sufficient supply of thyroid hormones (TH). TH deprivation during the late fetal period, or delay in TH replacement therapy in infancy may result in hearing impairment (HI) [1][2][3]. Deaf-mutism and HI are common in areas of iodine deficiency [4] and were reported in patients with congenital hypothyroidism (CH) prior to the implementation of thyroid neonatal screening in the 1980s [5].…”

Understanding hormone and hormone therapies' impact on the auditory system

“…This is partly due to the hormone's direct role in cochlear biological processes since TH as well as its receptors have been observed in the inner ear via immunohistochemical experiments. Subjects that have low levels or lack TH exhibit deformed OHCs as well as defects in afferent synaptic pruning and delays in calcium (Ca 2+ ) clustering in IHCs, ultimately leading to hearing loss (review in Andrade et al, ; O'Malley, Li, & Turner, ; Sundaresan et al, ). Additionally, TH regulates glutamate uptake by cerebellar astrocytes, and T3 treatment has been shown to protect against glutamate toxicity (Mendes‐de‐Aguiar et al, ).…”

Congenital Hypothyroidism and the Deleterious Effects on Auditory Function and Language Skills: A Narrative Review

“…The development of auditory pathways depends on the presence of adequate serum levels of thyroid hormones (TH) and their action on TH receptors (1)(2)(3). These hormones regulate proteins and enzymes responsible for the structural formation of the inner ear, being crucial for the proper performance of auditory function (4).…”