Patterns of hearing loss in tympanic membrane perforation resulting from physical blow to the ear: a prospective controlled cohort study.

OBJECTIVES: To evaluate the incidence and pattern of hearing loss in non-explosive blast injury of the ear.

STUDY DESIGN: Prospective clinical study.

SETTING: Tertiary referral centre.

PARTICIPANTS: Consecutive patients who suffered physical blow to the ear resulting in tympanic membrane perforations without history of previous middle ear disease.

MAIN OUTCOME MEASURES: Incidence of conductive and sensorineural hearing loss, extent of air-bone gap versus size and site of perforation, post-healing hearing loss recovery.

RESULTS: Fifty-one patients, 31 males (61%) and 20 females (39%) aged 10-56 years, were recruited over a 30 month study period. The prevalence of hearing loss was significantly more in the injured ears than contralateral normal ears (chi(2) = 76.26; P = 0.000). Pure conductive hearing loss occurred in 39%, while 28% (14 patients) had mixed hearing loss. Three patterns of sensorineural loss were observed: dip involving several adjacent high frequencies, a dip in a single frequency, and two separate dips involving low and high frequencies. The extent of air-bone gap correlated with the size of perforation (r = 0.33; P = 0.01). Ears that sustained small tympanic membrane perforation showed significantly small average air-bone gap (t = 2.97; P = 0.005). The mean air-bone gap difference between the anterior and posterior perforations was not significant (t = 1.7; P = 0.09). Closure of air bone gap following healing was significant (t = 15.08; P < 0.01), while recovery of bone conduction abnormality was less favourable.

CONCLUSION: Conductive hearing loss occurring in the speech frequencies was the most common form of hearing loss in this group of patients with non-explosive blast injury to the ear. The accompanying sensorineural loss mostly affected several adjacent high frequencies. Healing of perforation favoured significant recovery of the conductive loss, but recovery of sensorineural loss was less favourable.