To describe characteristics of sensorineural hearing loss
(SNHL) in patients with blast-induced tympanic membrane (TM) perforations that required surgery.
A retrospective review of hearing outcomes in those who had tympanoplasty for combat blast-induced TM perforations. These were sequential cases from one military otolaryngologist from 2007 to 2012. A total of 87 patients were reviewed, and of those, 49 who had appropriate preinjury, preoperative, and long-term audiograms were included. Those with pre-existing hearing loss were excluded. Preinjury audiograms were used to assess how sensorineural thresholds changed in the ruptured ears, and in the contralateral ear in those with unilateral perforations.
The mean time from injury to the final postoperative audiogram was 522 days. In the ears with TM perforations, 70% had SNHLs of 10 dB or less (by bone conduction pure tone averages). Meanwhile, approximately 8% had threshold shifts >30 dB, averaging 50 dB. The strongest predictor of severe or profound hearing loss was ossicular discontinuity. Thresholds also correlated with bilateral injury and perforation size. In those with unilateral perforations, the SNHL was almost always larger on the side with the perforation. Those with SNHL often had a low-to-mid frequency threshold shift and, in general, audiograms that were flatter across frequencies than those of a typical population of military personnel with similar levels of overall hearing loss.
There is a bimodal distribution of hearing loss in those who experience a blast exposure severe enough to perforate at least one TM. Most ears recover close to their preinjury thresholds, but a minority experience much larger sensorineural threshold shifts. Blast exposed ears also tend to have a flatter audiogram than most service members with similar levels of hearing loss.