1.
Mapping, speech perception, and language outcomes for children using
cochlear implants who have a preterm and/or low birth weight history.
Shani
1,2,
Dettman
Shiow Yuan
1,
Oh
Richard
1,2,3
Dowell
The University of Melbourne, Department of Audiology & Speech Pathology, 2 The HEARing Cooperative Research Centre,
3 Royal Victorian Eye & Ear Hospital
1
Background to this study.
A ‘premature’ or ‘preterm’ infant is defined as a live-born infant with a birth weight of 2500g
or less and/or a period of gestation less than 37 completed weeks (American Academy of Pediatrics, 2004; Engle, 2006; Harding, 2007;
World Health Organisation). As a consequence of advancements in prenatal, obstetric and neonatal care, the survival rates for children
born preterm (<37 weeks' gestational age), with a low birth weight (<2500 grams), or both, have improved substantially over the last two
decades. Children born very preterm (<33 weeks' gestational age) with very low birth weight (<1500 grams) are estimated to comprise
0.7% to 2% of all live births (Draper, Zeitlin, Field, Manktelow, & Truffert, 2007; Roberts & Lancaster, 1999). Despite improved survival
rates, these children often have co-morbid cognitive, physical and neurological disabilities further complicated by permanent sensorineural hearing loss (Picard,
2004; Streppel, et al., 1998). The extent to which the sensorineural hearing loss has an ‘in-utero’ or neonatal onset remains unclear, as the hearing loss may be
due neonatal hypoxia and/or hyperbilirubinaemia or the provision of treatments (eg. ototoxic drugs) designed to aid survival.
The aim of this study was to examine whether variables known to impact communication outcomes for full-term children using CIs (who
have sensorineural hearing loss as their single diagnosis), would have the same impact on preterm children using CIs. Specifically, it was hypothesized that
preterm children with longer gestational age, greater birth weight, lesser cognitive delay, more residual hearing, shorter duration of profound loss, communication
mode with an aural/oral emphasis, larger electrical dynamic range, less difficulty with mapping and programming, higher socioeconomic status (SES), and younger
age of implantation would demonstrate better speech perception and language outcomes.
Total number of children
who received CI at
Melbourne CIC
1987 – 2011
N = 700
n= 30 children with
gestational age
<37 weeks, and/or
birthweight < 2500
grams
n=25 subjects
Methods & Materials. A retrospective analysis of over 700 audiological and medical records from the Melbourne paediatric
n=19 subjects able
to complete
either/both
language and
speech perception
testing
database identified 25 children (10 females and 15 males) who met the following inclusion criteria; congenital hearing loss, born < 37
weeks gestational age and/or < 2500 grams in birth weight, and implanted for at least one year. Average gestational age was 28.20
weeks (range 23.60 to 35 weeks, SD 3.76), with n=4 preterm (> 33 and <37 weeks), n=13 very preterm (> 26 and <33 weeks) and n=8
extremely preterm (<26 weeks). Average birth weight was 1040 grams (range 524 to 2430 grams, SD 525.92). Two were preterm
with low birth weights (<2500 grams), n=9 were very preterm with very low birth weights (<1500 grams), and n=7 were extremely
preterm with extremely low birth weights (<1000 grams). Birth weights for the remaining 7 children were unknown. The mean unaided 3-frequency pure tone
average (PTA) for the best ear was 108.11 dB HL (range 85 to 123 dB HL, SD 10.16), mean duration of profound deafness was 2.93 years (range 0.76 to 7.21
years, SD 1.38), and mean age at implantation was 3.80 years (range 1.55 to 15.47 years, SD 2.83). Children completed the open-set CNC monosyllabic
word test (Peterson & Lehiste, 1962), the Bench-Kowal-Bamford (BKB) open-set sentence test (Bench & Bamford, 1979), and language tests where suitable
(either Peabody Picture Vocabulary Test [PPVT-III, Dunn & Dunn, 1997], Rossetti Infant-Toddler Language Scale [RI-TLS, Rossetti, 1990], Preschool Language
Scales [PLS-4, Zimmerman, Steiner, & Pond, 2002], and/or Clinical Evaluation of Language Fundamentals [CELF-4 & CELF Preschool, Semel, Wiig, & Secord,
1992, 1996]). The nature of the child’s response to the ‘map’ programming stimuli was analyzed during the switch on period (weeks 2 to 6 post surgery) and at one
mapping review appointment at 12 months post implant. An educational psychologist also completed testing of cognitive abilities for all children.
n=19 subjects able
to complete
language testing
n=13 subjects able
to complete
speech perception
testing
Excluded n=670
excluded n=1 did not
proceed with CI due
to significant aided
residual hearing &
N=4 with < 6 mo
device experience
n= 6 subjects
unable to complete
language or
speech perception
testing
n=3 able to
provide only MRL
response to
auditory stimuli in
mapping
Results. The speech processor was able to be programmed accurately for 22 out of 25 cases. For Case 2 and 14 with severe
15
Mean Growth Rate = 0.84
Range 0.01 to 3.12
SD
10
0.74
5
0
10
5
0
0
5
10
15
20
dettmans@unimelb.edu.au
www.hearingcrc.org
creating sound value
Figure 2. Open-set word scores, scored for words correct, for
n=13 preterm children using CIs compared with published data.
10
Figure 3. Open-set sentence scores for n=13 preterm children
using CIs compared with published data.
5
0
0
Chronological Age (years)
Figure 4. Individual receptive language trajectories for
n=15 preterm children using CI.
Figure 1. Open-set word scores, scored for phonemes correct,
n=13 preterm children using CIs compared with published data.
15
Equivalent Language Age (yrs)
15
Equivalent Language Age (yrs)
Equivalent Language Age (years)
cognitive delay and Case 21 with a moderate cognitive disability and cerebral palsy, only a maximum response level (MRL) (eg blink
signifying loudness discomfort level) could be obtained at switch-on and at 12-months post implant. The mean open-set word (OSW)
scores for n=13 children who completed testing were 76.8% phonemes (range 48 to 91%; SD 12.7) and 51.8% words (range 12 to
84%; SD 21.0). The mean open-set sentence score was 70.5% (range 18 to 98%; SD 25.7). Figures 1, 2 and 3 (see right) compare
individual pre-term childrens’ scores with mean scores from children with typical gestational age and birth weight (Dowell, et al., 2002a;
Dowell, et al., 2002b; Eisenberg, Kirk, Martinez, Ying, & Miyamoto, 2004; Geers, et al., 2003).
Educational psychologist’s testing indicated the cognitive status for the pre-term children was within the normal range (n=10),
borderline average (n=1), mild delay (n=6), moderate delay (n=3) and severe global delay (n=5). Stepwise linear regression analysis indicated a relationship
between degree of cognitive delay/impairment and all speech perception outcomes. Neither gestational age, birth weight, gender, PTA, communication mode,
SES, nor age at CI were predictive of speech perception outcomes for this small group.
For n=19 children who completed language testing, the mean language delay was 50.19 months (range 6.64 to 125.87 months; SD
30.38). For the n=15 children who completed 2 or more tests over time, the average receptive language slope was 0.84 (range 0.01 to 3.12; SD 0.74, Figure 4
below), where a value of 1.0 indicates the normal vocabulary acquisition rate for hearing peers. Younger age at implant was associated woth better receptive
vocabulary for this group.
Figure 5 (below) illustrates the receptive language outcomes for n=19 preterm children using CIs (filled black circles) compared to
n=163 children (clear diamonds) with typical birth history using CIs (Dettman, Hoenig, Dowell, & Leigh, 2008). The solid grey line represents language growth for a
child with normal hearing. In Figure 6 (below) the normal growth line was adjusted (dashed blue line) for the group average age at implant, so that the progress of
these pre-term children is compared to their hearing age. On this ‘hearing age’ basis, all pre-term children, except Case 3 and 4, performed within one standard
deviation of their hearing peers.
5
10
Chronological Age (yrs)
Figure 5. Individual receptive language results (filled black
circles) for n=19 preterm children using CI compared with
results for full-term children using CI (clear diamonds).
15
0
5
10
Chronological Age (yrs)
15
Figure 6. Individual receptive language results (filled black
circles) for n=19 preterm children using CI compared with
results for full-term children using CI (clear diamonds). Dashed
blue line indicates expected language growth for ‘hearing age’,
ie adjusted for mean 3.8 years age at implant.
Case Study; Subject 6, an extremely preterm
child (24 weeks gestational age with
undocumented birth weight), had auditory
neuropathy and normal cognitive skills, used an
Aural/Oral communication mode and received
bilateral implants sequentially at the age of 1.55
and 4.03 years respectively. This child achieved
language scores within 7 months of
chronological age, had a standard score
between 85 and 100 on both PPVT-III and PLS-4,
and demonstrated a receptive language growth
rate of 1.32 over a period of 3.61 years. Subject 6
obtained
83%
(OSWphonemes),
60%
(OSWwords) and 98% (BKB sentences).
Conclusions.
Variables known to influence speech perception and language outcomes in full-term children with CIs also affect children with a pre-term/low birth weight
neonatal history. There were 3 children for whom the degree of cognitive delay was associated with no measurable implant benefit on formal speech perception and language
tests (but quality of life benefits were not measured in this study). These 3 children were able to give only a maximum (blink) response during mapping. In contrast, there were 13
children for whom substantial speech perception and language benefits were demonstrated. There were exceptional cases such as Case 6 with normal language growth. A
complex range of factors must be considered when discussing outcomes for this population.
Acknowledgements to the children, parents, speech pathologists, audiologists, surgeons & administrative staff at the Cochlear Implant Clinic, RVEEH, Melbourne, Australia.