To Örebro University

OBJECTIVE: Comparison of asymmetric hearing in patients with severe-to-profound hearing loss (STPHL) and those with less pronounced or no hearing loss. The influence of asymmetric hearing on cochlear implantation (CI) was also analyzed.

STUDY DESIGN: Retrospective cohort.

SETTING: Hearing clinics across all regions in Sweden. PATIENTS: This study included 898,421 adult patients identified using the audiometric software Auditbase and 4286 adult patients from the Swedish National Quality Register for STPHL.

MAIN OUTCOME MEASURES: Proportion of patients with asymmetric hearing according to 11 different asymmetry criteria. Adjusted odds ratios for the presence of cochlear implants, adjusted for age, sex, and the highest level of education.

RESULTS: Across the different criteria, asymmetric hearing ranged from 20% to 59% in STPHL patients and 14% to 46% in those with better hearing. Adjusted odds ratios showed that cochlear implants were more common in patients with >15 dB asymmetry in the pure tone average at the base and mid-range frequencies.

CONCLUSION: This study of national audiogram data from Sweden showed that asymmetric hearing was more common in patients with STPHL. The higher proportion of CI in patients with asymmetric hearing indicates that asymmetric hearing is a complicating factor that must be considered in the rehabilitation of STPHL.

Severe-to-profound hearing loss (STPHL) can negatively impact a patient’s life in many ways. Adequate assessment and rehabilitation are imperative. Reliable numbers on prevalence are important to inform the need for adequate allocation of resources to this vulnerable group. Most patients with STPHL are equipped with hearing aids (HAs) and approximately 10% have received a cochlear implant (CI). The aims of this thesis were to establish a valid prevalence of STPHL in Sweden and to study aspects affecting audiological rehabilitation including asymmetric hearing loss. Furthermore, we wanted to explore the vestibular function in patients with acquired sensorineural STPHL.

In the first study we collected audiograms from 20 of 21 regions in Sweden and found a STPHL prevalence of 0.28%. We could not find a correlation between prevalence and cochlear implantation rate across regions. The second study utilised data from the Swedish national quality register for adult patients with STPHL. Patients with sensorineural hearing loss are three times more likely to receive a CI than patients with mixed hearing loss. More than 90% of the patients in the register experience good or very good benefit from the rehabilitation independent of whether they have received HAs or a CI. In the third study we compared prevalence of asymmetric hearing between patients with bilateral STPHL and those with better hearing. Asymmetric hearing was more common when STPHL was present. We found that CIs were more frequent in patients with asymmetric STPHL. Lastly, the fourth study examined 47 patients with STPHL and 51 age- and sex-matched controls regarding vestibular function. Vestibular function was evaluated with the caloric test, video head impulse test (vHIT), and vestibular-evoked myogenic potentials (VEMP). The caloric test and vHIT showed statistically significant negative impact from STPHL, emphasizing that vestibular evaluation and subsequent rehabilitation should be considered for STPHL patients.

In conclusion, this thesis has produced a valid prevalence of STPHL in Sweden. Additionally, it revealed that asymmetric hearing is common, and vestibular function may be affected in patients with STPHL.

Background: The prevalence of disabling hearing loss is increasing worldwide. However, previous studies on hearing loss prevalence have enrolled small populations or only provided estimates.

Aim: To establish the prevalence of severe-to-profound hearing loss (STPHL) in the adult Swedish population and compare it with the cochlear implantation rate in Sweden.

Material and methods: We established a database containing over 15 million audiograms obtained from regions covering > 99% of the Swedish population by extracting audiogram data from the computer software application, Auditbase. We used this database to calculate the percentage of adult patients with bilateral hearing levels >= 70 dB. We collected data regarding cochlear implantations in Sweden from the National Board of Welfare and Health.

Results: The prevalence of STPHL in the adult Swedish population was 0.28%. There were regional variations in the prevalence and rate of cochlear implantation; however, there was no association between both parameters.

Conclusions: This study presents an updated and reliable prevalence figure for STPHL in Sweden.

Significance: Patients with STPHL have extensive rehabilitation requirements; accordingly, it is important to determine the accurate prevalence of STPHL to inform the allocation of adequate resources.

Severe-to-profound hearing loss (STPHL) can affect a person negatively in many ways. Audiological rehabilitation is important for these patients. Patients receiving cochlear implants make up less than 10% of this group but have been studied extensively. In 2005, a national registry for adult patients with STPHL was introduced in Sweden. Its purpose was to evaluate and improve rehabilitation for all patients with STPHL. Data from the Swedish registry for adult patients with STPHL were used to evaluate variables affecting the audiological rehabilitation. Previous published data from the registry were reviewed, and new data from the follow-up questionnaire were presented. More than 90% of patients rehabilitated with hearing aids experienced a good or very good benefit of audiological rehabilitation. Tinnitus and vertigo affected quality of life negatively and were reported by many patients with STPHL (41% and 31%) at follow-up. To maintain the high number of patients who find audiological rehabilitation beneficial, individualized treatment plans and timely re-evaluations are crucial. Tinnitus and vertigo need to be addressed repeatedly in the rehabilitation process.