Aim Consideration of how treatment for hypothyroidism may lead to an improvement in hearing, illustrated by two cases of hearing loss identified by neonatal screening.
Method Two babies referred for Audiological assessment and identified to have a sensorineural hearing loss showed an improvement in their hearing levels following management for hypothyroidism. The literature was searched for information regarding the association of thyroid problems and hearing loss to elucidate an explanation for the improvement in hearing when hypothyroidism was treated.
Results The sensorineural hearing loss in two babies showed an improvement following treatment for hypothyroidism. Baby A (14 August 2007) initially had a hearing loss of 50–60 dBnHL. Hypothyroidism was identified by the Guthrie test simultaneously with readmission with neonatal jaundice. There is a strong family history of thyroid disorder. A now has normal hearing. Baby B (18 September 2009) was diagnosed with a mild to moderate loss and aided. B has agenesis of the thyroid. B's hearing has improved to a unilateral mild loss. In 1888 the Myxoedema Committee of the Clinical Society of London found hearing loss in over half the adults studied. By the mid 1950s it was agreed that the loss may be ‘perceptive’ and hearing improved in about half the cases treated with thyroid extract. Autosomal recessive Pendred's syndrome is a known cause of hearing loss associated with thyroid dysfunction in which hearing loss is not thought to respond to thyroid replacement therapy. Research into the postulated ways that hypothyroidism could cause hearing loss supported the theory that thyroid treatment can sometimes lead to an improvement in auditory function. Direct physical problems for example due to oedema are postulated along with neuronal function, maturation and myelination effects.
Conclusion Early identification and management of hypothyroidism can improve any related sensorineural neonatal hearing loss in specific cases. Hypothyroidism in the neonate should be identified and treated as it is may be a reversible cause of hearing loss in addition to other problems. The improvement of hearing loss with thyroxine treatment is probably multifactorial but includes maturation and improved neurological function.