What causes hearing loss in Haemophilus influenzae type b (Hib) meningitis?

Updated: Jul 09, 2018
  • Author: Prateek Lohia, MD, MHA; Chief Editor: Niranjan N Singh, MBBS, MD, DM, FAHS, FAANEM  more...
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Answer

Hearing impairment is a common complication of meningitis. It is among the most common sequelae of Hib meningitis, occurring in about 20% of cases, although reports indicate a range of 10-30%. Hearing loss is sensorineural and may be unilateral or bilateral, with deficits ranging from mild hearing loss to deafness in the involved ear. Persistent hearing deficits may be associated with learning disabilities and language delay.

The actual mechanisms of damage to the hearing system are not fully understood. The absence of all waveforms on brainstem auditory evoked response (BAER) testing in these patients suggests a peripheral process. One explanation of injury is that, during the acute phase of illness, the eighth cranial nerve becomes encased by inflammatory exudate within its sleeve in the subarachnoid space.

Another possible mechanism is bacterial invasion of the spiral ganglia or cochlear perilymph via the internal auditory canal or cochlear aqueduct, resulting either in direct damage or in damage secondary to toxins or inflammatory products. Evidence for either of these mechanisms has been found in pathological studies.

Although sensorineural hearing loss is the most common finding, occasional patients with postmeningitic deafness are found to have conductive hearing loss. This type of deficit may result from the otitis media that fairly commonly precedes the development of Hib meningitis. Unlike sensorineural hearing loss, conductive hearing deficits resolve without permanent impairment.


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