The impact of cochlear implantation on quality of life: The role of audiologic performance and variables

Abstract

OBJECTIVE: The purpose of this study was to assess the impact of cochlear implantation (CI) on health-related quality of life (HRQOL), to correlate the results with audiologic performance, and to analyze the influence of variables that possibly affect the CI outcome.

STUDY DESIGN: A retrospective study.

SUBJECTS AND METHODS: Fifty-six adult CI users were evaluated by two HRQOL-questionnaires (the Nijmegen Cochlear Implant Questionnaire [NCIQ] and the Medical Outcome Study Short-Form 36 [SF-36]) and speech-perception tests (Freiburger monosyllable and Hochmair, Schulz, Moser (HSM) sentence test).

RESULTS: The NCIQ showed significant improvements in the total score and in all subdomains after CI. The NCIQ total score and the advanced sound-perception and speech-production score correlated significantly with speech test results. Significant inverse relationships were noted between speech test results and duration of deafness. Significant associations were found between time since CI, NCIQ total score, and speech test results.

CONCLUSION: The NCIQ was able to detect significant effects of CI on HRQOL and correlated with audiologic measures, supporting its use as a measurement tool in CI.

For many years, cochlear implantation (CI) has been a well-established procedure for patients with profound sensorineural hearing loss.¹ From the outset, the assessment of patient benefits associated with CI has been a continuing focus of implant research. Besides the purely audiologic performance, the gains in terms of quality of life and activities and participation are important outcomes when evaluating results in this particular category of patients (World Health Organization). In the case of CI, this means that the treatment not only affects hearing and speech production daily but also has an impact on self-esteem, activities and social functioning. Over the past 10 years, the general health status of patients, often referred to as health-related quality of life (HRQOL), has become more and more the focus of research. Most existing HRQOL questionnaires for CI users focus predominantly on measuring auditory functioning and some associated social activities, so they can hardly be classified as disease-specific HRQOL instruments. In 2000, Hinderink et al² developed a disease-specific HRQOL questionnaire for adult CI users: the Nijmegen Cochlear Implant Questionnaire (NCIQ). The NCIQ is a quantifiable self-assessment HRQOL instrument that encompasses not only hearing and speech production but also self-esteem, daily activities, and social functioning. The positive effects of a CI on HRQOL were shown in all publications using this questionnaire, although not many researchers have yet used the NCIQ.^2–6

The aim of the present study was to examine the impact of cochlear implantation on different aspects of HRQOL in postlingual deaf adult patients using the new disease-specific NCIQ and a generic questionnaire (Medical Outcome Study Short-Form 36 [SF-36]). The results of both HRQOL instruments were compared and correlated to speech-perception scores. Furthermore, the influence of variables (age, duration of deafness, and time since CI) on HRQOL outcomes and audiologic test results was analyzed.

PATIENTS AND METHODS

Study Population

The study was approved by the institutional review board. Sixty-two postlingually deaf adult subjects, who were implanted with a multichannel CI at the ENT Department of Charité from 1995 to 2005 and who had had their implant for a minimum of 12 months, were identified. Demographic data (current age, age at intervention, and time since intervention) were collected for each person from patient records.

HRQOL Instruments

The following instruments were used to obtain data on HRQOL: the NCIQ and the SF-36. Two copies of both HRQOL instruments, together with a letter in which the purpose of the study was explained, were separately mailed to 62 CI patients. The first version was for the pre-CI state and the second version for the post-CI state.

The NCIQ, a disease-specific HRQOL questionnaire recently designed and validated, is composed of 6 subdomains. Basic sound perception, advanced sound perception, and speech production constitute the physical domain; self-esteem comes under the psychological domain; and activity limitations and social interactions make up the social domain.^2,3 Each subdomain contains 10 items. These items are formulated as statements with five answer categories that vary from “never” to “always” (55 statements) or from “no” to “good” (five statements). If a statement does not apply to a patient, a sixth answer can be given: “not applicable.” The questionnaire was scored as described by Hinderink et al.² Scores range from 0 (very poor) to 100 (optimal). The NCIQ² was translated by a native German and a native English speaker group into a German version by using forward-backward translation.

The SF-36 is a non-disease-specific, generic HRQOL instrument.⁷ It contains 36 items that measure 8 domains: physical functioning, role functioning due to physical health problems, role functioning due to emotional problems, bodily pain, vitality, social functioning, mental health, and general health perceptions. The number of response choices per item range from two to six. Item scores on each dimension are coded, totaled, and transformed into a scale from 0 to 100, in which higher scores indicate better self-perceived health. A physical component summary score and a mental component summary score can be computed using the standardized scoring system.

Additional Questions

Our survey had three additional questions: (1) “For how long had you been deaf when you received your CI?” (2) “For how many hours per day do you use the CI?” and (3) “Are you satisfied with the changes in the quality of life after CI (never, sometimes, regularly, usually, and always)?”

Auditory Performance

To relate the outcome of the HRQOL instruments to the subjects' auditory performances, we used their results from the Freiburger monosyllable test in quiet (70 dB SPL) and the HSM sentence test in noise (70 dB SPL, S/N = 15 dB). A total of 54 (87%) CI users participated in both speech tests.

Statistical Analyses

Statistical analysis was performed by using STATISTICA 6.0 for Windows (StatSoft, Inc., Tulsa, Oklahoma). Differences between parameters (pre/post-CI scores) or data were analyzed by using the nonparametric Wilcoxon test for paired observations. The Spearman correlation was used to identify and quantify relationships between HRQOL scores, results of the auditory performance, and the other implant variables.

RESULTS

Demographic Characteristics

A total of 56 (90%) CI users returned the NCIQ and the SF-36, 20 males and 36 females. The mean age of the study group at the time of implantation was 50.2 years (standard deviation, 14.4 years; range, 21–72 years). The length of time of deafness before implantation varied from 0.5 to 34 years, with a mean length of 10.2 years (SD, 10.8 years). The mean duration of CI experience at the time of completing the questionnaire was 4.0 years (SD, 2.8 years; range, 1–10.1 years). All the patients received a multichannel implant. The most commonly used type was the Nucleus CI24 Contour (Cochlear Ltd., Sydney, Australia) (n = 15). The distribution of the different implant systems together with demographic characteristics are shown in Table 1. Altogether, 50 (89.2%) patients reported that they are always/usually satisfied with the changes in quality of life after CI.

Significant Improvements in all NCIQ Scores

CI was associated with a significant increase in HRQOL, as measured by the NCIQ (Fig 1 and Table 2). The NCIQ showed significant (P <.001) improvements in the total score and in all 6 subdomain scores after CI. The largest differences between pre-CI and post-CI scores were for basic (65%) and advanced sound perception (52%). The differences for the other four subdomain scores were >30%.

Ambiguous SF-36 Results

The SF-36 detected significant improvements after CI in the following domains: social functioning (P = .000054), mental health (P = .0016) and general health perception (P = .026), and in the mental summary score (P = .00049) (Table 3). In contrast, the physical functioning score (P = .038) and the physical summary score (P = .047) decreased significantly.

Table 1

Characteristics of study population

Characteristic
Sex (no.)
Male	20
Female	36
	Mean (SD)	Range
Age at study (y)	54.3 (14.0)	22–76
Age at implant (y)	50.2 (14.4)	21–72
Duration of deafness (y)	10.2 (10.8)	0.5–34
Cochlear implant use (y)	4.0 (2.8)	1–10.1
Implant type (no.)
CI 24 Contour	15
CI 24M	13
C40 +	13
CI22	5
Pulsar	5
Freedom	3
C40	2

Figure 1

NCIQ-results. Compared with the pre-CI state, the NCIQ measured significant improvements in the subdomains 1–6 and in the total score post-CI (P <.001). The box contains the values for 50% of cases from the 25th (Q1) to the 75th (Q2) percentile; the length of the box corresponds to the interquartile range (IQ).The line through the box is the median value. A point beyond an inner fence (Q1-1,5xIQ; Q2 + 1,5xIQ) on either side is considered a mild statistical anomaly (“o”).

Significant Relationships Between the NCIQ Scores and Results of Speech Tests

Improvements in the NCIQ total score after CI correlated with the results in speech-perception tests (monosyllable test: r = 0.28, P = .037; HSM sentence test: r = 0.29, P = .033) (Table 4). The results of the correlation analysis have shown a significant direct correlation between the post-CI scores of the advanced sound-perception subdomain with both speech test results (monosyllable test: r = 0.43, P = .0012; HSM sentence test: r = 0.45, P = .00076). Furthermore, there was a significant correlation between speech-perception tests and post-CI score for the speech-production subdomain (monosyllable test: r = 0.56, P = .000012; HSM sentence test: r = 0.39, P = .0041).

Significant Associations Between SF-36 Scores and Results of Speech Tests

When mean post-CI scores of the SF-36 were analyzed together with the speech-perception scores, some relationships were detected; the mean SF-36 scores of the domains physical functioning (r = 0.40, P = .02) and vitality (r = 0.44, P = .0087) correlated significantly with the results of the monosyllable test. Furthermore, the scores of the SF-36 domains vitality (r = .50, P = .0027) and mental health (r = 0.38, P = .028) have shown significant relationships with the HSM sentence test.

Table 2

NCIQ results: Comparison of the pre-CI and post-CI scores

HRQOL score	Pre-CI	Post-CI
Total	31.3 (15.1)	69.2 (13.8)^*
Basic sound perception	15.8 (19.8)	71.6 (16.6)^*
Advanced sound perception	18.8 (17.3)	65.4 (16.0)^*
Speech production	52.1 (24.6)	85.7 (13.6)^*
Self-esteem	33.9 (16.4)	60.8 (17.8)^*
Activity	31.3 (16.7)	64.5 (16.6)^*
Social interactions	35.9 (18.9)	67.8 (16.5)^*

Values are mean and standard deviation. Significant changes are indicated with an asterisk (^* P <.001).

Table 3

SF-36 results: Comparison of the pre-CI and post-CI scores

HRQOL score	Pre-CI	Post-CI
Physical functioning	81.0 (27.0)	71.9 (31.3)^*
Role functioning (physical)	70.3 (42.3)	64.3 (43.7)
Pain	80.1 (31.2)	70.5 (32.0)
General health perception	61.3 (22.2)	64.2 (21.4)^*
Vitality	55.1 (24.7)	61.0 (23.9)
Social functioning	33.8 (31.7)	70.4 (36.1)^†
Role functioning (emotional)	73.7 (41.4)	75.2 (40.4)
Mental health	56.9 (24.4)	70.3 (21.0)^*
Physical summary score	50.9 (11.5)	46.9 (11.3)^*
Mental summary score	39.1 (12.3)	49.6 (9.1)^†

Values are mean and standard deviation. Significant changes are indicated with an asterisk (^* P < .05, ^† P < 0.001).

Analysis of Variables That Possibly Affect HRQOL and/or Speech-Perception Results

There was only one significant relation between these variables and HRQOL scores. Current age correlated with the post-CI speech-production score (NCIQ) (r = 0.34, P = .019). No other relationships were found between current age or age at implantation and HRQOL scores for both questionnaires or speech test results.

No significant associations were found between the NCIQ results and the length of hearing loss. In contrast, significant relations were detected between the post-CI scores of the SF-36 domain physical functioning (r = 0.39, P = .049) and the physical summary score (r = 0.46, P = .026) and the length of deafness. However, statistically significant inverse relationships were seen between post-CI speech test results (monosyllable test: r = −0.38, P = .016; HSM sentence test: r = −0.38, P = .014) and the duration of deafness before implantation.

Analysis of the ratio of deafness to age at implantation revealed no statistically significant relationships with HRQOL scores of both questionnaires. But as this ratio increased (as subjects spent a greater portion of their lives deaf), speech tests diminished significantly (monosyllable test: r = −0.36, P = .019; HSM sentence test: r = −0.44, P = .0037).

When the mean post-CI scores of both HRQOL instruments were analyzed, together with the duration of CI use, the following associations were detected: time since CI correlated significantly with the NCIQ total score (r = 0.34, P = .0094) and scores of the advanced sound-perception (r = 0.48, P = .00019), speech-production (r = 0.32, P = .015), self-esteem (r = 0.26, P = .049), and activity (r = 0.27, P = .037) domains; with the scores of the physical functioning (r = 0.46, P = .0067), role functioning (physical) (r = 0.46, P = .0073), pain (r = 0.43, P = .012), general health perception (r = 0.50, P = .0029) SF-36 domains; and with the mental- (r = 0.38, P = .039) and physical summary scores (r = 0.52, P = .0028). Significant associations were also found between the results of speech tests (monosyllable test: r = 0.34, P = .011; HSM sentence test: r = 0.29, P = .033) and time since intervention.

Table 4

Spearman results of correlation analyses (r = correlation coefficient) on NCIQ and SF-36 scores and speech-perception tests after CI

HRQOL score	Freiburger monosyllable test in quiet 70dBSPL r	HSM sentence test in noise 70dBSPL, S/N 15dB r
NCIQ
Total	0.28^*	0.29^*
Basic sound perception	0.12	0.18
Advanced sound perception	0.43^*	0.45^†
Speech production	0.56^†	0.39^*
Self-esteem	0.12	0.25
Activity	0.18	0.25
Social interactions	0.20	0.24
SF36
Physical functioning	0.40^*	0.33
Role functioning (physical)	0.15	0.21
Pain	0.28	0.21
General health perception	0.20	0.18
Vitality	0.44^*	0.50^*
Social functioning	0.14	0.11
Role functioning (emotional)	−0.14	0.06
Mental health	0.20	0.38^*
Physical summary score	0.25	0.18
Mental summary score	0.09	0.32

Significant correlations are indicated with an asterisk (*P <.05, ^† P < .001).

The average duration of implant use per day in our patients was 14.4 hours. The average daily duration of implant use was more than 12 hours in 92% of the subjects and more than 16 hours in 39%. There was no significant correlation between the total number of daily hours for which the CI was used and the results in speech-perception tests or the results of both HRQOL instruments.

DISCUSSION

CI has become the method of choice for the treatment of postlingually deaf patients. As experience with the assessment, surgery, and rehabilitation of deaf patients has increased, the selection criteria have also changed. Studies investigating the effect of a CI on different aspects of HRQOL and audiologic performance are important to give realistic expectations to our patients. In the current study, these effects were measured by using a new disease-specific HRQOL questionnaire, the NCIQ. The questionnaire was able to detect significant effects on several HRQOL aspects, including the social and psychological domains, and correlated with audiologic measures, supporting its use as a measurement tool in CI. Furthermore, the duration of deafness and time since intervention were identified as variables with significant influence on the CI outcome.

The results of our study are once more proof that CI is indeed a successful treatment for improving quality of life and speech recognition for deaf patients. The benefit of CI has been shown by the fact that a large proportion of our subjects (89.2%) were always or mostly satisfied with their CI. Furthermore, 92% of our patients were using their CIs for more than 12 hours a day; the average duration was 14.4 hours. This corresponds to findings in the literature.^2,8,9 The NCIQ, previously tested and found to be reliable and valid and have good internal consistency among CI users,^2–4 measured significant improvements in all 6 domains between the pre-CI and post-CI assessments. The positive effect of cochlear implantation on HRQOL has been described by others, although not many researchers have used the NCIQ.^2–6 Hinderink et al² found significantly beneficial effects of a CI in all subdomains, which were equivalent to our results. The largest differences between pre- and post-CI scores were, according to our results, for basic and advanced sound perception. The differences for the other 4 subdomains were smaller, but the benefits of a CI on these domains have also been shown by an average rise in score of 30%. Recently, Cohen et al⁴ used the NCIQ to compare HRQOL between 26 CI users and 30 hearing aid users, all with postlingual deafness. The results of their analyses supported the value of this instrument in both groups, and results for CI users corresponded to those in our studies.

When analyzing the SF-36 scores, we detected ambiguous results. The decreased scores in the domain of physical functioning and in the physical summary score in this study could be possibly natural effects of aging.⁶ Significant improvements of the mental health and mental summary score in our study suggest better psychical functioning after CI.¹⁰ Finally, in SF-36 validation studies, hearing loss may best be reflected in the categories of role-emotional, social functioning, and vitality.⁷ Among these three domains, only the impairment of the social functioning score was detectable after CI. In general, our findings seem to confirm the variable SF-36 results after CI mentioned by Krabbe et al.³ A lack of sensitivity of the SF-36 in detecting changes in HRQOL after CI was also seen in earlier studies.^6,11 Therefore, on the basis of the previous studies and our observations of low sensitivity, we agree with Damen et al⁶ that the SF-36 should not constitute the first-choice generic quality of life questionnaire to evaluate hearing-impaired patients.

In our study, some significant correlations were detected between post-CI NCIQ scores and the results in speech-perception tests; the NCIQ total score and scores for the subdomains of advanced sound perception and speech production were significantly related to the results in speech-perception tests. The finding that improved audiologic performance brings about positive changes in HRQOL is also supported by the study of Cohen et al.⁴ They found increased overall HRQOL scores and benefits in all subdomains. The more audiologic improvement patients had, the greater their overall HRQOL benefit. Francis et al⁸ reported that, in their study, improvements in speech perception are predictive of gains in HRQOL and associated with emotional benefits after cochlear implantation. Previous studies have found positive correlations between quality of life improvement and speech-recognition performance after cochlear implantation.^9,12 These are interesting findings because other authors have reported a lack of significant correlation between user satisfaction and audiologic test results.^2,13 Although significant relationships were only detectable between NCIQ subdomains of advanced sound perception and speech-production and speech-recognition performance after CI, significant improvements of HRQOL were measured in all of the subdomains, so it can be argued that the patients' subjective perception of benefits because of CI is not directly linked to the performance level. Our results indicate that the effect CI has on HRQOL might even outweigh improvements in hearing ability measured by speech-perception tests. This emphasizes the need for a CI-specific HRQOL instrument, in addition to existing sound- and speech-perception tests, to evaluate the outcome of CI in a more complex way.

Duration of deafness, time since intervention, age, and etiology are additional variables that may also contribute to speech-perception results and overall HRQOL outcome of CIs. Analysis of relations between length of hearing loss and HRQOL measured with the NCIQ revealed no significant associations. A similar result was determined by Cohen et al.⁴ Furthermore, the finding that current age or age at implantation is not directly linked to HRQOL or speech test results is also supported by our study.^12,14 On the other hand, the duration of deafness has had a strong influence on our CI outcome. Inverse relationships were seen between the duration of deafness before CI and post-CI speech test results. The effect of a longer duration of deafness before CI being correlated with lower postoperative speech test results has been described by other authors.^15,16 In their study, Leung et al¹⁷ investigated the relationship between CI outcome and the ratio of duration of deafness to age at implantation. This factor, first analyzed in detail by Tyler and Summerfield,¹⁸ is related to the DURAGE measure, the duration of deafness divided by patient age, first hypothesized by Shipp and Nedzelski¹⁵ as a predictive index. They found a greater ratio had a negative impact on performance with a CI because patients who had spent a greater portion of their life in deafness had worse outcomes. This agrees with our results; as this ratio increased (as subjects spent a greater portion of their lives deaf), post-CI speech tests diminished significantly. Thus, early identification of deaf adults may further enhance the benefit received from CIs.

In our study, significant associations were found between the NCIQ total score and scores of the following subdomains: advanced sound perception, speech production, self-esteem and activity, and the duration of CI use. This is not in accordance with the articles by Damen et al⁶ and Cohen et al⁴; both also measured HRQOL with the NCIQ. Damen et al⁶ observed a small but not significant trend toward deterioration over time, and they concluded that this deterioration could, for example, be a natural effect of aging.⁶ Furthermore, our data suggests, in agreement with Vermeire et al., that speech-perception scores still continued to increase over time, even after long-term CI use.¹⁴ They analyzed the speech reception results as a function of time and found a significant improvement in speech recognition over time. Similarly, Damen et al⁶ found that patients significantly increased the initial improvement in speech recognition after cochlear implantation over 6 years.⁶ These are interesting findings because other authors have shown no increase in speech-perception outcomes or merely an improvement over a shorter follow-up period.^19,20

A few points regarding the study design are relevant. HRQOL data from the pre-CI state was collected retrospectively, possibly leading to recall bias. Like Cohen et al,⁴ we found no association between time since intervention and HRQOL benefit scores, indicating that the passage of time alone did not result in greater improvement in post-CI HRQOL.⁴ To minimize the influence of patients' pre-CI answers on their post-CI answers, the pre- and post-CI questionnaires were sent separately.

Additionally, Hinderink et al² showed that retrospectively collected pre-CI HRQOL data from CI users was comparable to prospective HRQOL scores from patients with profound hearing loss on a CI waiting list.² However, the extent of recall bias in cochlear implant patients may be minimal, given that the patients are not cured of their deafness and re-experience their impairment whenever they remove their speech processor. To summarize, we can state that the NCIQ was able to detect significant effects of a CI on several HRQOL aspects, including the physical, social, and psychological domains and correlated with audiologic measures, supporting its use as a measurement tool in CI. Our findings that patients' subjective perception of benefits because of CI was not completely related to the performance level emphasize the need for a CI-specific HRQOL instrument, in addition to speech-perception tests, to evaluate the complex CI outcome. Our results suggest that variability of duration of deafness and time since intervention may influence the overall outcome of CI- HRQOL and audiologic performance. Further study is needed to elucidate the relative importance of these and other factors. Standardized CI-specific HRQOL instruments are highly recommended because they will make it possible to compare the results of different CI studies and to monitor the effects of technical improvements to CIs in the future.

AUTHOR INFORMATION

From the Department of Otorhinolaryngology, Campus Virchow Klinikum, Charité-Universitätsmedizin, Berlin.

Corresponding author: Priv. Doz. Dr Heidi Olze, Department of Otorhinolaryngology, Campus Virchow Klinikum, Charité-Universitätsmedizin Berlin, Augustenburger-Platz 1, 13353 Berlin, Germany.

E-mail address: heidi.olze@charite.de

AUTHOR CONTRIBUTIONS

Anke Hirschfelder, study design, data collection; Stefan Gräbel, data collection, statistical analyses, speech-perception tests; Heidi Olze, study design, data collection, writer.

FINANCIAL DISCLOSURE

None.

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