HIPOTIREOIDISMO CONGÊNITO COMO FATOR DE RISCO PARA OS TRANSTORNOS DO PROCESSAMENTO AUDITIVO CENTRAL

A Study on the Effects of Hypothyroidism on the Senses: A Comprehensive Narrative Review

Hypothyroidism has been found to have long-term effects on each of the senses, but with proper treatment, many of them can be significantly minimized. This paper analyzes the research on the impact of hypothyroidism on the senses of smell, taste, hearing, vision, and thermoregulation. Data were collected from the National Library of Medicine, PubMed, and Google Scholar databases using the keywords "hypothyroidism," "taste," "smell," "vision," "hearing," and "thermoregulation." Approximately 413 articles were found when searching with these parameters, and 30 were used in this paper. Studies were excluded if they were outside this paper's scope or older than 2012. Studies were included if they specifically focused on hypothyroidism and one of the five listed senses. Patients with hypothyroidism had a significantly increased risk of sensorineural hearing loss, decreased perception of the blue-yellow color axis, decreased sense of olfaction and number of olfactory bulbs, and decreased thermogenesis. Hypothyroidism was also found to show increased length of COVID-19-induced anosmia and decreased bitter taste perception. It can be concluded that hypothyroidism has many effects on the senses, particularly an increased risk of sensorineural hearing loss. More studies need to be done on these effects.

Cognitive and White Matter Microstructure Development in Congenital Hypothyroidism and Familial Thyroid Disorders

CONTEXT

Children with congenital hypothyroidism (CH) are at risk for suboptimal neurodevelopment.

OBJECTIVES

To evaluate neurocognitive function and white matter microstructure in children with permanent or transient CH and to correlate these findings with disease severity.

DESIGN, PARTICIPANTS AND METHODS

A retrospective and prospective observational study was conducted in 39 children with permanent or transient CH, and in 39 healthy children. Cognitive function was assessed by Wechsler Intelligence Scale, Fourth Edition, and by other tests; the white matter microstructure was investigated by 3 Tesla magnetic resonance imaging.

RESULTS

Children with permanent CH have lower cognitive scores at a median age of 9.5 years than those with transient CH and controls. An IQ score between 71 and 84 was found in 28.6% of permanent CH and of <70 (P = 0.06) in 10.7%. The Processing Speed Index (PSI; P = 0.004), sustained visual attention (P = 0.02), reading speed (P = 0.0001), written calculations (P = 0.002), and numerical knowledge (P = 0.0001) were significantly lower than controls. Children born to mothers with Hashimoto's thyroiditis have significantly lower IQ values (P = 0.02), Working Memory Index (P = 0.03), and PSI (P = 0.02). Significantly lower IQ and Verbal Comprehension Index values were found in children with a family history of thyroid disorders (P = 0.004 and P = 0.009, respectively). In children with permanent CH, significant correlations between abnormalities in white matter microstructural, clinical, and cognitive measures were documented.

CONCLUSIONS

These findings indicate that children with CH are at risk of neurocognitive impairment and white matter abnormalities despite timely and adequate treatment. The association between offspring cognitive vulnerability and maternal thyroid disorders requires careful consideration.

Dysfunction of the Auditory System in Children With Hypothyroidism: A Systematic Review and Meta-Analysis

OBJECTIVE

To examine the prevalence of hearing impairment in children with hypothyroidism, and to characterize clinical and subclinical hearing loss by examining cochlear function, auditory brainstem pathways, and integration of the auditory system as a whole.

DESIGN

An electronic search was conducted using PubMed, Scopus, and Cochrane Library databases. This systematic review was performed in accordance with the PRISMA guidelines. Original observational studies that utilized audiological tests for auditory system evaluations in hypothyroidism were included. A total of 2004 studies were found in the search, with 23 studies meeting the inclusion criteria.

RESULTS

The pooled prevalence of hearing loss was 16.1% [95% confidence interval 10.7, 22.4] for children with congenital hypothyroidism. Hearing thresholds at pure-tone averages (0.5-2 kHz) were 1.6 dB [95% confidence interval 1.7, 4.8] higher for children with hypothyroidism compared to age-matched controls. Cochlear dysfunction was detected at middle frequencies (1-3 kHz) by otoacoustic emission testing, indicating abnormalities of hair cell function or cochlear integration. Retrocochlear involvement was detected on auditory brainstem response (ABR), with prolonged Wave I indicating a peripheral conduction abnormality localized to the middle or inner ear and eighth cranial nerve.

CONCLUSIONS

Children with hypothyroidism have a higher prevalence of hearing loss than children without hypothyroidism. For children with congenital hypothyroidism, evidence of subclinical abnormalities at the level of the cochlea and eighth cranial nerve are present despite early initiation of levothyroxine therapy. Dysfunction of the auditory system might begin with predominance of peripheral conduction abnormalities early in development.

Neonatal thyrotropin levels and auditory neural maturation in full-term newborns

Objective

This study aimed to look for a possible relationship between thyrotropin (TSH) values from neonatal bloodspot screening testing and newborn lower auditory pathway myelinization evaluated using the brainstem evoked response audiometry (ABR) test.

Methods

Sixty-two healthy full-term newborns without perinatal problems were enrolled in the study. TSH results were collected from neonatal bloodspot screening data and were below the test cut-off level (15μUI/mL). The TSH test was performed between three and seven days, and the ABR test was performed in the first 28 days of life. The newborns were divided into two groups: Group 1 (n = 35), TSH between 0 and 5μUI/mL, and group 2 (n = 27), TSH between 5 and 15μUI/mL. Data are presented as mean ± SD, median, or percentage, depending on the variable.

Results

Wave latency and interpeak interval values for Groups 1 and 2 were as follows: Wave I: 1.8 ± 0.1 and 1.7 ± 0.1; Wave III: 4.4 ± 0.1 and 4.4 ± 0.1; Wave V: 6.9 ± 0.1 and 6.9 ± 0.1; interval I–III: 2.6 ± 0.1 and 2.6 ± 0.1; interval I–V: 5.1 ± 0.1 and 5.1 ± 0.1; interval III–V: 2.4 ± 0.1 and 2.4 ± 0.1. There were no significant differences in ABR parameters between groups 1 and 2 (p > 0.05). Multiple regression analysis showed a slight significant negative correlation between TSH and wave I values (standardized β = −0.267; p = 0.036), without observing any relationship with the other ABR waves recorded.

Conclusions

This study investigated the relationship of TSH and auditory myelinization evaluated by ABR. It did not show a significant change in lower auditory pathway myelinization according to TSH levels in newborns with TSH screening levels lower than 15 μUI/mL.

Hearing outcome in infants following correction of maternal hypothyroidism during pregnancy

PURPOSE

There is significant prevalence of overt and subclinical hypothyroidism in pregnant women in rural areas. Maternal hypothyroidism is known to cause congenital hypothyroidism resulting in sensorineural hearing loss. Anti-Thyroperoxidase antibodies are known to cross placental barrier. There is no literature on hearing assessment in infants born to women whose hypothyroidism was corrected during pregnancy. Do these infants suffer hearing loss? Our study addresses this question.

METHODS

140 infants born to women on treatment for hypothyroidism during pregnancy and 140 infants born to euthyroid women were evaluated for hearing by Brainstem Evoked Response Audiometrry at 1 and 4 months age. Anti-TPO antibodies were estimated at 4 months of age.

RESULTS

There was no clinical hearing deficit or delay in neurological development in infants born to women undergoing treatment for hypothyroidism during pregnancy. However wave V latency on BERA was slightly prolonged in them compared to infants born to euthyroid women. There was absence of wave V when maternal subclinical hypothyroidism persisted till parturition. However within 6-8months of age the wave V latencies corrected to normal. Anti-TPO antibodies were within normal range at 4months age.

CONCLUSION

Maternal hypothyroidism when corrected before parturition does not affect hearing in the infants clinically. The mild delay in wave V on BERA corrects within first year of life. However larger studies to assess hearing in infants born to women having overt hypothyroidism during first trimester of pregnancy may be desirable to assess whether hearing is adversely affected in them.

Familial-Related Risks for Congenital Hypothyroidism in Iranian Newborns: A Population-Based Case-Control Study

BACKGROUND

Congenital hypothyroidism (CH), as one of the most common endocrine disorders, is a preventable cause of mental retardation.

OBJECTIVE

This study aimed to identify familial-related risk factors for CH in Iranian newborns.

METHODS

A population-based case-control study was performed on the National Registry System of patients with CH in Iran. In this study, 906 controls and 454 cases were studied for one year. Familial related factors were investigated using logistic regression models. Population attributable fraction (PAF) was also calculated for each significant risk factor.

RESULTS

Using multivariate analysis, an increased risk for CH was observed in patients with congenital anomalies (odds ratio (OR): 5.77, 95% confidence interval (CI): 2.37 - 14.01), history of mental retardation in family (OR:2.10, 95% CI: 1.15-3.83), mother's hypothyroidism during pregnancy (OR: 2.01, 95% CI: 1.33 - 3.03), intra-family marriage (OR:1.49, 95% CI: 1.18 - 1.89), gestational diabetes (OR: 1.69, 95% CI: 1.09 - 2.63), having a hypothyroid child in the family (OR: 2.48, 95% CI: 1.39 - 4.42), and twins or more (OR: 2.61, 95% CI: 1.31 - 5.21). The highest PAF among familial-related risk factors for CH is related to the intra-family marriage (14.9%).

CONCLUSIONS

This study revealed that familial-related risk factors and consanguine marriages play an essential role in the high incidence of CH in Iran. About 15% of CH in Iran could be attributed to intra-family marriage alone.

Congenital hypothyroidism as a risk factor for hearing and parents' knowledge about its impact on hearing

Aim

To evaluate the hearing of children with congenital hypothyroidism (CH) and to analyze the knowledge that parents’ have on the possible auditory impacts of the disease.

Methods

A total of 263 parents/guardians were interviewed about aspects of CH and hearing. Audiological evaluation was performed on 80 participants, divided into two groups: with CH (n= 50) and without CH (n=30). Clinical and laboratory CH data were obtained from medical records, pure tone auditory thresholds and acoustic reflexes were analyzed. The auditory data was compared between groups. Student’s t-test and Chi-square were used for statistical analysis at a significance level of 5% (p ≤0.05).

Results

The majority (78%), of the parents were unaware that CH when not treated early is a potential risk to hearing. There was no correlation between socioeconomic class and level of information about CH and hearing (p>0,05; p=0.026). There was a statistically significant difference between the auditory tone thresholds of the groups and between the levels of intensity necessary for the triggering of the acoustic reflex. The group with CH presented the worst results (p≤0.05) and absence of acoustic reflex in a normal tympanometric condition.

Conclusions

Children with CH are more likely to develop damage to the auditory system involving retrocochlear structures when compared to healthy children, and that the disease may have been a risk factor for functional deficits without deteriorating hearing sensitivity. The possible impacts of CH on hearing, when not treated early, should be more publicized among the parents/guardians of this population.

Self-reported participation restrictions in normal hearing individuals in thyroid ontogeny: Evidence of subclinical changes

Purpose

To verify evidence of subclinical alterations through self-reported participation restrictions in normal hearing individuals and congenital hypothyroidism patients.

Methods

An analytical, quantitative, cross-sectional exploratory study with a 1:1 ratio, consisting of a convenience sample of 86 normal hearing individuals with (n = 42) and without (n = 44) congenital hypothyroidism diagnosis. All participants underwent tonal and speech audiometry, immitance and distortion product otoacoustic emissions. The researchers excluded people with hearing loss, genetic syndromes and metabolic diseases. The instrument used for evaluate of self-reported participation restrictions was the HHIE-adapted questionnaire, composed of 25 questions, 12 of which were social domain and 13 emotional domain. Student's t-test and chi-square test were used for statistical analysis at a significance level of 5%.

Results

There was a significant (p < 0.001) self-reported participation restrictions in CH (61.9%), with a greater relevance for the social domain (p = 0.002). There was a greater frequency of mild/moderate (40.5%) and higher prevalence of association with clinical factors and adherence to treatment.

Conclusion

The findings indicate that self-reported participation restrictions in normal hearing individuals with congenital hypothyroidism was more significant than in the non-exposed group, suggesting evidence of subclinical auditory abnormalities in this population.