Describing hearing in individuals with cerebral palsy

Abstract

Hearing impairment is an associated problem in cerebral palsy, described as a ‘sensation’disturbance.1 Hearing is measured with a test battery that includes pure-tone and speech audiometry.2,3 Reducing these measurements to one meaningful number is problematic. Hearing data, collected in studies such as Bhasin et al. and Reid et al.4,5 and registries,6 may underreport hearing impairment by using pure-tone average (PTA) definitions of >40 dB Hearing Level (HL)4 or >70dB HL6 often without noting impairment type, configuration, or any changes over time. Applying the framework of World Health Organization’s International Classification of Functioning, Disability and Health (ICF), hearing test results represent body structure and function, but hearing also affects communication activity and participation.7–10 Hearing impairment filters, distorts, or blocks information from the brain, negatively affecting receptive and sometimes expressive communication.3 Environmental (e.g. background noise, room reverberation, and unfamiliar talker) and personal factors (e.g. age and sex) influence communication participation.8,9 Children, especially those with multiple disabilities, may need more sensitive hearing when acquiring language.2,3 Childhood hearing impairment occurs when a threshold in either ear is >20dB HL at any of the pure-tone frequencies routinely tested (e.g. 250, 500, 1000, 2000, 3000, 4000, 6000, 8000Hz).11 Comparing serial tests determines if impairments are stable, temporary, progressive, or fluctuating. Pure-tone results are described by degree (normal to profound), configuration (e.g. flat, sloping, rising, scoop, notch), and type (conductive, sensorineural, mixed). For example, if pure-tone air-conduction thresholds in the right ear are 25dB HL at 250 and 500Hz, 35dB HL at 1000Hz, 45dB HL at 2000Hz, 60dB HL at 4000Hz, and 75dB HL at 8000Hz, and bone-conduction thresholds are consistent with air-conduction thresholds, the impairment is described as a mild-to-severe,12 sloping, sensorineural hearing impairment in the right ear. The left ear results are reported separately. A number of issues encountered in epidemiological studies of hearing impairment have not been resolved: Degrees of impairment are not standardized. These classifications are only a naming convention and do not describe hearing difficulty at a communication activity or participation level.3,9 Even a ‘slight’ to ‘mild’ hearing impairment affects listening in important life situations.3 (See Table S1 to compare several hearing information classifications). For example, ‘severe’ is defined as 50–70,2 61–80,13,14 65–84,4 or 71–90dB HL.12 Pure-tone results (with at least six air-conduction and five bone-conduction thresholds per ear per testing date) are difficult to accurately summarize. One summarization method for air conduction thresholds is a PTA of two or more thresholds in one ear. PTA ignores type and configuration effects on speech understanding. This method was designed as a crosscheck procedure of a speech reception threshold, not as a measure of hearing impairment. PTAs do not allow estimations of which speech sounds are audible.2,3 A 2-tone or 3-tone PTA excludes important speech information from the higher frequencies such as words containing voiceless fricatives (e.g./s/,/f/). A mild-to-moderate, sloping sensorineural impairment and a moderate-to-mild, rising conductive impairment could have the same PTA but quite different effects on speech understanding. Two alternative methods attempt to decrease the data points while still capturing part of the configuration: a low- and a high-frequency PTA; or a low-, a mid-, and a high-frequency PTA. These PTAs could be reported with type of hearing impairment. Data collection frequency and timing should consider that hearing may fluctuate over a lifespan. Some conductive impairments improve with surgical/medical interventions or with children’s development. Most sensorineural impairments do not improve; some progressively worsen. Mixed hearing impairment can improve if the conductive component resolves. Cerebral palsy researchers and registries should weigh these issues and provide rationales for consensus definitions. At a minimum, if hearing impairment is categorized by degree of impairment, the chosen classification system2,4,12–14 must be identified with the data method given (i.e. actual thresholds, a threshold averaging process, or some other method). Components of a hearing ICF core set may prove useful8 in describing hearing and hearing impairment roles in a person’s daily functioning and participation.2,3,8,9 Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.