Cochlear Implantation in Patients with Known Cognitive Impairment: What are the Benefits?

Abstract

Objective:

To evaluate the outcomes of cochlear implantation (CI) in adults with preoperatively diagnosed cognitive impairment.

Study Design:

Retrospective cohort study.

Setting:

Tertiary-care academic center.

Patients:

Adults undergoing CI with preexisting cognitive impairment.

Interventions:

Cochlear implantation.

Main Outcome Measures:

1) Hearing improvement following CI; 2) Morbidity and mortality associated with surgery.

Results:

Eight patients met inclusion criteria with mean age 77.8 years (SD 9.6 years) at time of implantation; 7 were included in subsequent analysis as one did not have speech recognition scores. Average preoperative MoCA cognitive score of 22.6 (SD 3.9, ≤25 demonstrates cognitive impairment). Average follow up was 29.0 months (SD 33.3 months). Two patients passed away at an average 58.0 months (SD 31.1 months) after surgery. Median preoperative pure tone average (PTA) was 86.3 dB HL (IQR 31.3 dB HL) compared to 33.8 dB HL (IQR 5.0 dB HL) postoperatively (p=<0.001). Median preoperative speech testing score (AzBio/HINT) was 21% (IQR 24%) compared to 44% (IQR 21%) postoperatively (p=<0.001). There were no observed surgical complications during the follow up period.

Conclusions:

This study demonstrates that patients with cognitive impairment prior to CI can experience improved hearing, no increased risk of complications, and good longevity following CI. Further prospective studies are needed to further define the utility of CI in patients with impaired cognition.

Introduction

The impact of hearing loss on cognitive function in older adults is an active area of research as several studies attempt to better characterize and understand the complex relationship. Multiple studies have demonstrated that there is an association of cognitive decline in older adults with hearing loss compared to those with normal hearing(1–7). Multiple hypotheses have been proposed to explain the relationship between hearing loss and cognitive decline, including shared neuropathology or “common cause”, neuroanatomic changes in the brain auditory cortex, increased cognitive load of hearing loss, and the social isolation hypothesis(8,9). Psychosocial factors require emphasis, as social isolation resulting from difficulty to communicate is known to increase the risk for cognitive decline(10). It is also important to note that there may be a scoring artifact as a result of hearing loss when testing for cognitive function, as many tests rely on auditory processing(11,12).

Several studies have described the positive impact of treating hearing loss with amplification on cognitive decline, but understanding the neurocognitive impact of cochlear implantation (CI) is an area of active clinical research. Recent literature has demonstrated a lower rate of progression of cognitive impairment, improved quality of life and improved communication ability in patients who have undergone CI(13–22). There is little known, however, about the impact of CI in patients with preexisting cognitive impairment or dementia and whether it mitigates the risk of progressive cognitive impairment. When a patient has known cognitive impairment, is it worthwhile to offer a CI?

In the present study, we aim to examine CI outcomes in patients with pre-existing cognitive impairment. Adults with cognitive impairment are often overlooked as potential CI candidates, despite the benefits CI may provide in terms of hearing, quality of life, and cognitive function. The primary objective of this study is to describe hearing outcomes in adults undergoing CI with preexisting cognitive impairment. The secondary objective is to identify the morbidity and mortality associated with CI surgery in this unique population. The ultimate goal of this study is to provide guidance on the utility and benefits of CI in patients with preoperatively known cognitive impairment.

Materials and Methods

After institutional review board approval (IRB_00105049), the Utah Population Database (UPDB) was used to identify all patients over the age of eighteen years who received CI between 1994 to 2019. CPT code 69930 (cochlear device implantation, +/− mastoidectomy) was used to generate the initial patient query. From this list, patients were filtered for a first dementia/cognitive impairment diagnosis ICD code being record prior to undergoing CI. The ICD-9 diagnostic codes included the following: 290.0, 290.1x, 209.2x, 290.3, 331. The ICD-10 diagnostic codes included the following: F03.90, F03.91, G30.9. From this dataset, 60 patients were initially identified within the University of Utah Health system. A retrospective chart review of the demographic, audiologic and clinical data of all patients was performed. Inclusion criteria were age 18 years or older, documented cognitive impairment prior to implantation (either via formal testing or neuropsychology evaluation), and available audiologic testing data pre- and post-implantation. Complications were defined as any post-operative CI-related event requiring additional care (surgical site infection, meningitis, reimplantation, facial paralysis, CSF leak, etc.).

All patients who had formal cognitive testing underwent the Montreal Cognitive Assessment (MoCA), a validated cognitive assessment tool that helps determine the presence and degree of cognitive impairment. A MoCA score between 26–30 is considered normal, 18–25 is considered mild cognitive impairment, 10–17 is considered moderate cognitive impairment, and <10 is considered severe cognitive impairment.

Comparative analysis was performed using the independent samples median test. We considered P values of < .05 as being statistically significant. Analyses were done using IBM SPSS Statistics 28 software version 28.0.1.0 (released 2021, IBM SPSS Statistics for Windows; IBM, Armonk, NY).

Results

The initial UPDB patient query found 60 patients who underwent CI after a diagnosis of dementia/cognitive impairment. After performing a chart review, 8 patients met inclusion criteria. See Table 1 for descriptive data of this patient cohort. The mean age was 77.8 years (SD 9.6 years) at time of implantation. There were 7 males and 1 female. Regarding hearing loss etiology, 5 were noise/presbycusis, 1 was congenital, 1 was barotrauma, 1 was otosclerosis, and 1 was chronic ear disease. Six of the 8 patients were implanted initially on the right side whereas 2 were on the left side. Seven of the 8 patients used traditional hearing amplification for the contralateral ear at the time of implantation whereas 1 was unaided. Patient #4 did not have pre- or post-operative speech testing available in the electronic medical record, and was thus excluded from subsequent statistical analysis.

Table 1.

Patient cohort descriptive data. One patient (patient #4) did not have pre- or post-operative speech testing available in the medical record, and was thus excluded from the statistical analysis.

Patient #	Gender	Age at first CI (years)	HL etiology	Pre-operative dementia diagnosis	Cognitive Impairment Level	Preoperative MoCA Score	Time to implant from first dementia diagnosis (months)	Contralateral hearing modality	CI laterality	CI model	Complication
1	M	77	COM	unspecified	mild	25	1	HA	left	Med-El Flex24	no
2	M	78	otosclerosis	unspecified	mild	23	1	HA	left	AB Mid-Scala	no
3	M	80	noise	Alzheimer’s	mild	25	145	HA	right	Med-El Flex28	no
4*	F	88	noise/presbycusis	unspecified	mild	20	74	HA	right	Cochlear CI622	no
5	M	57	barotrauma	cerebellar atrophy	mild	23	90	HA	right	Cochlear CI622	no
6	M	86	presbycusis	unspecified	mild	23	9	HA	right	Cochlear CI622	no
7	M	74	congenital	unspecified	moderate	14	38	HA	right	AB SlimJ	no
8	M	83	noise/presbycusis	Alzheimer’s	mild	25	47	unaided	right	Med-El Flex24	no

CI: cochlear implant, COM: chronic otitis media, HL: hearing loss; MoCA: Montreal Cognitive Assessment; HA: hearing aid; AB: Advanced Bionics

Average preoperative MoCA cognitive score of 22.6 (SD 3.9). Six of the 7 patients were noted to have mild cognitive impairment at the time of CI whereas 1 was noted to have moderate cognitive impairment. Regarding etiology of cognitive impairment, 4 were unspecified, 2 were Alzheimer’s dementia, and 1 was cerebellar atrophy.

Median preoperative pure tone average (PTA) was 86.3 dB HL (IQR 31.3 dB HL) compared to 33.8 dB HL (IQR 5.0 dB HL) postoperatively (p=<0.001) on the implanted side. Median preoperative speech testing score (AzBio/HINT) was 21% (IQR 24%) compared to 44% (IQR 21%) postoperatively (p=<0.001) on the implanted side. See Table 2 for audiometric data for the implanted side.

Table 2.

Audiometric data for implanted side. One patient (patient #4) did not have pre- or post-operative speech testing available in the medical record, and was thus excluded from the statistical analysis.

Patient #	Pre-operative PTA	Pre-operative speech testing score	Post-operative PTA	Post-operative speech testing score
1	112.5	22	33.75	56
2	86.25	21	32.5	88
3	68.75	5	33.75	35
4*	66.25	N/A	32.5	N/A
5	96.25	17	28.75	44
6	60	32	37.5	34
7	100	32	33.75	52
8	77.5	8	50	41

PTA: pure tone average.

Average follow up was 29.0 months (SD 33.3 months). Two patients (patient # 1 and 2) passed away at an average 58.0 months (SD 31.1 months) after surgery, both due to reasons unrelated to CI surgery (abdominal infection and respiratory failure, respectively). There were no observed surgical complications during the follow up period.

Discussion

Cochlear implantation is the standard of care for treating individuals with severe-profound sensorineural hearing loss(23). For older adults with known known cognitive decline, though, is it worthwhile to perform this procedure? While it has been shown that CI is safe in patients with various levels of frailty, will a patient with impaired cognition benefit from surgery? Does their life expectancy with a neurodegenerative disorder justify a costly surgical intervention? Will they or their caregivers be able to derive benefit from the intervention, especially when post-operative auditory rehabilitation does require a significant amount of effort? This is a somewhat analogous clinical situation to caring for children with developmental delays. In this population, there have been studies showing the benefit of CI to both children with developmental delays and their caregivers(24,25). Could this similarly apply to older adults with cognitive impairment?

It is becoming increasingly established that the treatment of hearing loss has the potential to mitigate the risk of dementia and slow the rate of cognitive decline. In the present study, we aimed to identify the objective hearing and safety outcomes in patients undergoing CI with a pre-existing diagnosis of cognitive impairment or dementia. By utilizing the UPDB to identify and retrospectively review the present cohort, we found that patients with cognitive impairment prior to CI can experience improved hearing and good longevity following CI without any observed perioperative complications.

First established in 1982, the Utah Population Database (UPDB) is an extensive database providing access 11+ million individuals’ demographic details and clinical records in the setting of multi-generational pedigrees, including data encompassing diagnostic, surgical and discharge events. One strength of the UPDB lies in its ability to perform population-based analyses(26). Data that is stored in the UPDB and linked to person-oriented records reflect several events over an individual’s life. With this database, we were able to identify patients who underwent CI with a pre-existing diagnosis of dementia both before and after implementation of an electronic medical record. While only eight patients met initial inclusion criteria and were included in the study, with 7 included in the statistical analysis due to available speech recognition data, a total of sixty patients were identified to have underwent CI with a pre-existing diagnosis of dementia over a 25 year period.

Despite the demonstrated benefits of undergoing CI, a small percentage of CI candidates actually undergo implantation(27). Most agree that the primary barriers to CI include access limitations and understanding of candidacy. While several studies have demonstrated that CI is well tolerated by older patients(28–30), a recent study by Zhang et al demonstrated that the fear of undergoing CI surgery was one the primary barriers preventing CI candidates from receiving an implant(31). In the present study, the observed proportion of patients undergoing CI with pre-existing cognitive impairment does not reflect the observed prevalence of cognitive impairment in the general population(32). It is possible that a proportion of potential CI candidates are not referred as a result of their cognitive impairment diagnosis. A recently published study by our senior author demonstrated that older patients with cognitive impairment had greater cognitive benefits 1 year after CI compared to subjects with normal cognition(16). The present study adds to this data and demonstrates that CI is a safe and effective treatment modality for patients with severe-profound hearing loss and pre-existing cognitive impairment.

While several studies have examined the impact of traditional hearing amplification on cognitive decline, fewer studies have specifically looked at the role of CI as the treatment modality. The need for clinical research in this area has recently become evident and a handful of prospective studies have demonstrated improvements in global cognitive function after CI(13,33–35). Mosnier et al. demonstrated that patients with poor cognitive function prior to undergoing CI showed improved global cognitive function and a lower rate of progression to dementia compared to the general population after CI(13,14). An ongoing longitudinal study by Sarant et al. have observed no significant decline on any cognitive test score after CI(15). In the present cohort, there were unfortunately no postoperative cognitive tests recorded in the electronic medical record, and thus we are unable to determine if there was any improvement or decline in cognitive function after implantation. Based on recently published literature, however, it is becoming increasingly evident that CI has a likely positive impact on neurocognitive outcomes in older adults. It is reasonable to extrapolate this conclusion to patients with pre-existing cognitive impairment prior to CI. Future prospective studies evaluating the impact of CI on postoperative neurocognitive outcomes by objectively measuring cognitive scores are warranted.

Quality-of-life (QOL) improvement is an important outcome measure to consider when evaluating a patient’s daily experience. Previous studies have generally observed a largely positive effect on QOL after CI(17–20). McRackan et al evaluated the relationship between demographic, hearing- and CI-related factors and quality of life. Interestingly, they found that these factors only accounted for a small percentage of the QOL domain scores and concluded that factors not accounted for by these factors contribute to the observed improvements in QOL(36). In the present study, none of the included patients had documented QOL domain scores in the electronic medical record to determine whether CI had an objective benefit in this regard. To our knowledge, there are currently no published studies examining the impact of CI on QOL in patients with pre-existing dementia, highlighting an area of need for future clinical research.

The primary limitations to this study were its retrospective study design and the relatively small number of patients in the cohort meeting inclusion criteria. It is likely that a larger proportion of older patients who undergo CI have some component of cognitive impairment that has either never been formally diagnosed or has not been recorded as a diagnosis code in the electronic medical record, and were thus missed in the patient query.

In conclusion, this study demonstrates that patients with preoperative cognitive impairment can obtain significant benefit from cochlear implantation. Every patient in our cohort experienced improved hearing similar to the average CI user with no increased risk of complications, and maintained good longevity following CI. As a result, this study offers optimism and guidance in counseling of prospective patients with cognitive impairment on the utility and benefits of CI. However, further prospective studies are still needed to understand the full advantage of CI in adult patients with pre-existing impaired cognition.