Problems in assessing the audiogram in patients with severe hearing impairment

Abstract

Severe hearing impairment (SHI) is an impairment of hearing in which the air conduction mean over 0.5–4 kHz in the better hearing ear lies between 70 and 90 dB. Masking of bone and air conduction thresholds is seldom possible with SHI, leading to difficulties in assessing the pure tone audiogram whenever there is a potential air bone gap in either ear.An audiological survey of 83 patients with severe hearing impairment was conducted. In 16 per cent of patients there was no possibility of a material air bone gap in either ear and no difficulty in interpreting the audiogram. In 23 (28 per cent), the audiogram was consistent with, but did not prove the presence of, an air bone gap in the poorer hearing ear. In 25 patients (30 per cent of 108) the better hearing ear could not be determined, and in 22 (27 per cent) a profound sensorineural impairment in the poorer hearing ear could not be excluded. The implications of this for the otologist are discussed.

Bilateral hearing results of 751 unilateral stapedotomies evaluated with the Glasgow benefit plot

“…In addition, Ramsay and Linthicum 34 found that patients with pre-operative mixed hearing loss more frequently suffered profound post-operative sensorineural hearing loss (SNHL). 40 The current study identified the best pre-and postoperative bone conduction thresholds in unilateral hearing impairment patients, and the worst such parameters in bilateral asymmetrical hearing impairment patients, who would probably require post-operative hearing aids (Table III). The 1995 American Academy of Otolaryngology, Head and Neck Surgery guidelines, which use post-operative bone conduction thresholds for ABG calculation, have been criticised because bone conduction thresholds can change unpredictably.…”

“…For example, bone conduction thresholds may either improve, due to Carhart's effect, as a result of successful mobilisation of the ossicular chain, or worsen as a result of surgical trauma 36 – 39 . Bone conduction audiometry may have limitations owing to difficulties with masking, especially in cases of severe bilateral conductive hearing impairment 40 …”