Hearing Threshold Shifts Among 11- to 35-Year-Olds With Early Hearing Impairment.

OBJECTIVES: Data obtained from the clinical records of selected 11- to 35-year-olds with preadult onset hearing impairment were analyzed with 2 primary aims: (1) to determine the incidence of hearing threshold level (HTL) shift in this cohort and, (2) to examine the relationship between HTL shift, whole-of-life noise exposure, and other factors.

DESIGN: Cross-sectional cohort study. Retrospective HTL + survey data for a sample of 237 young Australians receiving hearing (re)habilitation services were obtained. From these data, two subsets, (A) n = 127 and (B) n = 79, were analyzed. Participants with risk factors for progressive hearing loss (other than noise exposure) were excluded from both subsets. Subset (A) additionally excluded cochlear implant recipients, and subset (B) excluded cases with diagnosis of hearing loss after age 5 years. Using subset (A) data, the differences between final (recent) and specified baseline (initial) HTLs at 250, 500, 1000, 2000, and 4000 Hz were calculated and three criteria for HTL shift were applied. Correlations between reported noise exposure and HTL shift were calculated (Mann-Whitney U test). Using subset (B) data, relationships between high frequency (HF) HTL shift and exposure, and other personal and extrinsic factors were examined (Cox Regression model). Survival analyses (Kaplan-Meier) were performed to reveal the temporal pattern of HF shift. The magnitude of HF shifts at 5, 10, and 15 years post initial (i.e., specified baseline) audiogram were also calculated.

RESULTS: For subset (A), HTL shift (≥15 dB any frequency, and/or ≥10 dB at two adjacent frequencies) was observed in 46.5% of cases examined. HF shift (≥15 dB at 2000 and/or 4000 Hz; one or both ears) was observed in 33.1% of cases. There was no relationship between HTL shift and reported whole-of-life exposure. For subset (B), no relationship was found between HF shift and noise exposure, nor 9 of 10 personal or extrinsic covariates tested. HF shift was significantly associated with HTL ≥ 70 dB at 2000 and/or 4000 Hz at initial audiogram. Survival analysis also illustrated that HF shift was more frequent, and occurred earlier, when HF hearing loss was ≥70 dB at initial audiogram. Median HF shifts at 15 years after initial audiogram were in the magnitude of 5 to 10 dB, and at the 90th percentile were 25 to 30 dB.

CONCLUSIONS: HTL shift was observed in almost 50% of cases without predisposing factors for progressive hearing loss. The magnitude of HF shift increased gradually over time. While no relationship was found between HTL shift and noise exposure, the interpretation of this finding is restrained by the small spread of whole-of-life noise exposures, within a relatively conservative range. Nevertheless, this is the first direct examination of the relationship between HTL shift and noise exposure in young people with preadult hearing impairment.