HSC Section 8_April 2017

observed in adults and children with bilateral hearing

loss. Specifically, the current study found that CNC

word recognition was, on average, 44% at 6-months post-

activation, whereas studies using adults with bilateral

hearing loss, also with 6 months of use, have an average

CNC word score of 61%.

The primary explanation for

this finding is that patients with normal hearing in one

ear continue to rely heavily on their good ear because of

the natural sound quality, which may reduce the rate of

improvement and maximum rehabilitation potential of

the deaf ear.

In contrast to speech recognition in quiet, the cur-

rent study found that speech recognition in noise was

not significantly improved after CI, although the scores

at 6-months postactivation were higher than those

obtained before surgery. As noted earlier, several previ-

ous investigators have reported similar findings. How-

ever, one recent study by Mertens et al. suggests that

speech-in-noise improvement may not emerge until after

several years of implant use.

In that study, 12 adults

with SSD and CI were followed through 36 months of

implant use. Speech-in-noise performance was measured

with CI

and CI

off

using various testing parameters,

including presentation of both speech and noise from the

front, as well as spatially separated signals (S

, S

). Results demonstrated improved speech in

noise for S

after 12 months of implant use, whereas

improved performance for S

was not observed until

36 months of implant use.

Tinnitus suppression continues to be an indirect

benefit of implantation among patients with SSD. As

seen in the current study, the majority of patients who

had tinnitus prior to surgery had a reduction in self-

reported tinnitus severity following implantation with

the device on, and in many cases also with the device

off. The exact underlying reason of tinnitus suppression

is not known, although there is speculation that the

implant increases afferent stimulation, which offsets one

possible underlying cause.

There are several limitations associated with the

current study. First, the relatively small sample size

makes statistical comparisons less robust and limits gen-

eralizability of the data. Larger sample sizes are needed

to understand the variability in performance within this

population. Another limitation is that data was collected

retrospectively from two separate centers, each with

unique test protocols. For example, center 2 measured

speech recognition in the implanted ear with the contra-

lateral ear plugged and muffed, whereas center 1 used

masking on the contralateral side. It is unknown if these

two methods are equivalent. Another limitation of this

study is the condition of the participants’ sound process-

ors. Each participant was tested using the sound proces-

sor and program that they use in everyday life. There

was no control regarding the volume setting, the pres-

ence of noise suppression circuits, or input mixing ratios.

It is possible that some participants have much higher

volume settings than others.

Demographic factors also limit the current study.

For example, the group studied here was comprised of

children and adults with various etiologies and dura-

tions of deafness. Although the majority (12 of 23 or

52%) had SSNHL, other causes of hearing loss were also

represented. The numbers, however, are not large

enough to analyze outcomes by etiology. In addition, lon-

ger durations of deafness were observed in many of

these cases. We know from previous work that duration

of deafness negatively impacts CI performance and may

have played a role in our patients being implanted after

longer periods of nonusable hearing.

Our mean dura-

tion of deafness (4.0 years) is skewed by three of six of

the children in whom congenital hearing loss and long

delays to implantation occurred. Future studies with

higher numbers of patients in this category will be

needed to determine if significant differences in perform-

ance occur.

CONCLUSION

Rehabilitation of SSD with CI significantly

improves speech understanding in the deafened ear and

reduces or eliminates tinnitus in most subjects. Speech

understanding in noise remains unchanged between the

3-months and 6-months postactivation test intervals. It

is possible that performance on speech in noise will con-

tinue to improve that and benefits will be realized with

longer-term implant experience.

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