Hearing Loss in Nicu Graduates

Due to early birth, premature organ development, and exposure to primary illnesses, premature babies are more prone to hearing loss. They may have consumed ototoxic drugs or acquired illnesses like jaundice, leading to hearing loss. 1-3-6 strategy is the screening test for hearing loss, i.e., the baby is screened at one month, diagnosis by 3 months, and rehabilitation should be started by six months. Even mild and unilateral hearing loss can cause significant delays. The types of hearing loss seen are sensory, conductive, auditory dyssynchrony/auditory neuropathy and central hearing loss.

Types of Hearing Loss

• Sensorineural hearing loss is the abnormal development or damage to the cochlea or auditory nerve cells.
• Conductive hearing loss is when signals are not conducted properly due to middle ear effusions, microtia, canal stenosis, and stapes fixation.
• Auditory neuropathy/ Auditory dysynchrony is a rare type of hearing loss where the signals transferred to the cochlea are normal. Still, the signals transferred from the cochlea to the auditory nerve are abnormal. It can be due to prematurity, birth asphyxia, bilirubin encephalopathy, or other genetic factors.
• Central hearing loss is when abnormal signal processing occurs at the central level.

Etiology

• 50% of congenital hearing loss is genetic in origin. Of these, 30% are syndromic causes, and the rest are non-syndromic. The most common genetic cause of non-syndromic autosomal recessive hearing loss is the mutation of Connexin 26 (Cx26) gene located on chromosome 13q11-12. There have been at least 90 deletions identified. Cx26 mutation causes at least 20-30% of congenital hearing loss.
• Deleting mitochondrial gene 12SrRNA, A1555G, is associated with predisposition for hearing loss after exposure to aminoglycoside antibiotics. The non-genetic causes include 25% of the cases of hearing loss. It is due to secondary causes like injury to the auditory system during the intra-peripartum period. The most common cause of non-genetic hearing loss is congenital CMV infection.
• Congenital CMV- 5% of the infants with CMV are asymptomatic. Hearing loss can occur in 10-15% of these, and they can be progressive. Oral valganciclovir is given for six months and can improve hearing function at 2 years. Ideal treatment has to be begun at 1 month of birth.
• The other risk factors include NICU stay for five days, ECMO, drugs like gentamycin and tobramycin, loop diuretics, and Total serum bilirubin>20 or present in the exchange zone. Syndromes associated with progressive or late-onset hearing loss include neurofibromatosis, usher, and osteoporosis. Other frequently identified syndromes include Waardenberg, Alport, Pendred, Jervell, and Lange-Nielson syndrome. The incidence of hearing loss in HIE requiring therapeutic hypothermia is 6-10%.

Also Read: DIARRHEA IN CHILDREN: TYPES OF ENTERIC INFECTIONS

Screening

• The screening tests are auditory brainstem response(ABR) and evoked otoacoustic emission(EOAE). The threshold cut-off to label as abnormal screening is greater than or equal to 35 dB. In ABR, the stimulus or response to clicks is checked using three scalp electrodes. It is reliable only after 34 weeks of age. Otoacoustic emission is acceptable for routine screening of low-risk infants, and for high-risk babies, auditory brainstem response is better and recommended because auditory brainstem response picks up all kinds of neural hearing loss, including auditory dyssynchrony.
• Evoked otoacoustic emission- It is based on the acoustic feedback from cochlea following a click or tone burst stimulus. It is quicker than auditory brainstem response and is more likely to be affected by debris or fluid. It has higher referral rates and is unable to detect auditory dyssynchrony.
• A pediatric audiology specialist should re-examine infants who fail the first test within three weeks. Follow-up testing will include full diagnostic frequency-specific auditory brainstem response, evoked otoacoustic emission, and middle ear evaluation(tympanometry using 1000 Hz probe tone).

Degree And Severity Of Hearing Loss

Rehabilitation And Treatment

• A personal amplification system (bone-anchored hearing aid-BAHA) will be fitted immediately. If the child has severe or profound bilateral hearing loss, that child is a candidate for a cochlear implant by the end of the first year. The last option is an auditory brainstem implant.

Prognosis

• Fitting of hearing aids by 6 months has been associated with improved speech outcomes. Initiation of early intervention services by 3 months has been associated with improved cognitive developmental outcomes at 3 years of age.

Also Read: 

Microdeletion Syndromes Part-3 : Williams Syndrome,  Rubinstein Taybi Syndrome, Smith Magenis  Syndrome

Infections of the Upper Airway- Common Cold and Sinusitis

Hope you found this blog helpful for your neonatology NEET SS pediatrics preparation. For more informative and interesting posts like these, keep reading PrepLadder’s blogs.