DEVELOPMENTAL MEDICINE & CHILD NEUROLOGY ORIGINAL ARTICLE
Intellectual disability in cerebral palsy: a population-based
SUSAN M REID
ELAINE M MEEHAN
SARAH J ARNUP
DINAH S REDDIHOUGH
1 Developmental Disability and Rehabilitation Research, Murdoch Children’s Research Institute, Melbourne, Victoria; 2 Department of Paediatrics, University of
Melbourne, Melbourne, Victoria; 3 Neurodevelopment and Disability, The Royal Children’s Hospital, Melbourne, Victoria; 4 Clinical Epidemiology and Biostatistics Unit,
Murdoch Children’s Research Institute, Melbourne, Victoria, Australia.
Correspondence to Susan M Reid, Developmental Disability and Rehabilitation Research, Murdoch Children’s Research Institute, 50 Flemington Road, Parkville, VIC 3052, Australia.
This article is commented on by Sigurdardottir on page 640 of this issue.
Accepted for publication 24th February
Published online 18th Apr 2018.
RRR Relative risk ratio
A population-based observational study design was used to describe the epidemiology
of intellectual disability in cerebral palsy (CP) in terms of clinical and neuroimaging
associations, and to report the impact of intellectual disability on utilization of health services
and length of survival.
Population CP registry data were used to retrospectively assess the frequency of
intellectual disability and strength of associations between intellectual disability and mobility,
epilepsy, vision, hearing, communication, and neuroimaging patterns (n=1141). Data linkage
was undertaken to assess usage of hospital inpatient and emergency department services.
Survival analysis was performed in a 30-year birth cohort (n=3248).
Intellectual disability, present in 45% of the cohort, was associated with non-
ambulation (47% vs 8%), later walking (mean 2y 7mo vs 1y 9mo), hypotonic (8% vs 1%) or
dyskinetic (9% vs 5%) CP, a quadriplegic pattern of motor impairment (42% vs 5%), epilepsy
(52% vs 12%), more emergency and multi-day hospital admissions, and reduced 35-year
survival (96% vs 71%). Grey matter injuries (13% vs 6%), malformations (18% vs 6%), and
miscellaneous neuroimaging patterns (12% vs 4%) were more common in people with
Intellectual disability adds substantially to the overall medical complexity in
CP and may increase health and mortality disparities.
Cerebral palsy (CP) is an umbrella term used to describe
individuals who, as a consequence of early disturbance to
the developing brain, have ongoing problems with move-
ments and/or postures that limit their ability to perform
activities of daily living.
Intellectual disability is an impor-
tant and relatively common accompanying impairment in
CP that has the potential to further affect daily activities,
burden of care, quality of life, effectiveness of interven-
tions, and longevity. Intellectual disability may also exacer-
bate existing health care disparities because of an increased
reliance on carers to identify illnesses and health care con-
cerns, challenging behaviours associated with intellectual
disability, and lower rates of participation in preventive
care and health promoting practices.
Intellectual disability in CP has not been well studied.
This research gap can be partly explained by the substan-
tial challenges posed by the use of standard measures of
intelligence for assessing children with CP.
Iceland and Australia estimated that one-third of children
with CP were unable to complete all tasks on such mea-
sures because of inadequate pointing and verbal ability
and, even among those who completed the tasks, summary
scores were likely to misrepresent the child’s actual level of
functioning by the inclusion of tasks that required speed or
ﬁne motor responses.
It is therefore not surprising that
estimates of the frequency of intellectual disability in CP
have varied between 38% and 52%, despite arising from
population samples and being based on the same cut-off of
a tested IQ less than 70.
The frequency of intellectual
disability has been reported to be relatively increased in
association with quadriplegia,
poor gross motor func-
We know of only one previous publi-
cation relating the prevalence of intellectual disability to
cerebral pathology. On the basis of classiﬁcation of pat-
terns of injury on brain magnetic resonance imaging
the highest rate of intellectual disability was seen
in individuals with cerebral malformations (>70%) and the
lowest in those with a predominantly white matter injury
The objectives of this study were to describe the epi-
demiology of intellectual disability in CP in terms of clini-
cal and neuroimaging associations, and to report the
impact of intellectual disability on utilization of health ser-
vices and longevity. We aimed to emphasize the
© 2018 Mac Keith Press DOI: 10.1111/dmcn.13773 687