Cognitive functioning in children with cerebral palsy

Abstract

Children with cerebral palsy (CP) have an increased risk of cognitive impairments. This narrative review of the literature discusses assessment of cognition in children with CP, presents the most salient characteristics of cognitive functioning pertaining to each subtype, and discusses the relationships between brain injury, functioning, and intervention from a developmental perspective. A search for original studies of cognitive functioning in children with different subtypes of CP was performed. The search resulted in 81 unique hits. There were few studies with a representative sample of children with CP where all participants were individually assessed. Cognitive functioning in children with the most severe motor impairments were often assumed and not assessed. Furthermore, there was a confounding of IQ below 70 and intellectual disability, possibly leading to an overestimation of the prevalence of intellectual disability. Longitudinal neuropsychological studies, including also very young children and those with the most severe speech and motor impairments, as well as intervention studies, are called for.

What this paper adds
Few studies have assessed cognition in a representative sample of children with cerebral palsy.
Cognition in children with severe motor impairment is often assumed, not assessed.
Lack of assessment may lead to overestimating the prevalence of intellectual disability.
Lowered cognitive functioning in older children highlights the need for longitudinal studies.

Full text

DEVELOPMENTAL MEDICINE & CHILD NEUROLOGY INVITED REVIEW
Cognitive functioning in children with cerebral palsy
KRISTINE STADSKLEIV
1,2
1Department of Clinical Neurosciences for Children, Oslo University Hospital, Oslo; 2Department of Educational Science, University of South-Eastern Norway,
Vestfold, Norway.
Correspondence to Kristine Stadskleiv, Oslo University Hospital, Department of Clinical Neurosciences for Children, Post Box 4950 Nydalen, N-0424 Oslo, Norway.
E-mail: kristine.stadskleiv@oslo-universitetssykehus.no
PUBLICATION DATA
Accepted for publication 6th December
2019.
Published online 9th January 2020.
ABBREVIATION
PVL Periventricular leukomalacia
Children with cerebral palsy (CP) have an increased risk of cognitive impairments. This narra-
tive review of the literature discusses assessment of cognition in children with CP, presents
the most salient characteristics of cognitive functioning pertaining to each subtype, and dis-
cusses the relationships between brain injury, functioning, and intervention from a develop-
mental perspective. A search for original studies of cognitive functioning in children with
different subtypes of CP was performed. The search resulted in 81 unique hits. There were
few studies with a representative sample of children with CP where all participants were indi-
vidually assessed. Cognitive functioning in children with the most severe motor impairments
were often assumed and not assessed. Furthermore, there was a confounding of IQ below 70
and intellectual disability, possibly leading to an overestimation of the prevalence of intellec-
tual disability. Longitudinal neuropsychological studies, including also very young children
and those with the most severe speech and motor impairments, as well as intervention stud-
ies, are called for.
The motor impairments of children with cerebral palsy
(CP), caused by an inborn or early acquired brain lesion,
1
are often accompanied by impaired functioning in other
areas, such as cognition. The scope of cognitive impair-
ments varies between and within the spastic, dyskinetic,
and ataxic subtypes.
2
The identification of cognitive
impairments depends upon the quality of the assessments,
and the first aim of this study is to review challenges in
that regard. In this review, cognitive functioning in chil-
dren with CP will be discussed from a developmental per-
spective, on the basis of a review of the literature on
cognitive functioning in children with CP.
Assessment of cognition
Two aspects of assessment of cognition need to be
addressed: the paucity of studies where a representative
sample of all subtypes have been assessed and the chal-
lenges involved in reliably assessing cognition in children
with impairments that makes test performance difficult.
The latter is partly responsible for the former. The Gross
Motor Function Classification System (GMFCS),
3
a5-
point ordinal scale where level I indicates the least impair-
ment, is typically used to classify motor impairment in the
literature discussing cognitive functioning. However, classi-
fication of fine motor functioning would have been even
more relevant.
There are some epidemiological studies based on data
from CP registries
4–6
and geographical cohorts,
7–10
but
few where a representative sample is individually
assessed.
11,12
Without assessment, IQ was estimated on the
basis of clinical judgement,
4,5
school placement,
13
degree
of gross motor impairment,
10
or interview with parents.
8
Assessing cognition in children with motor impairments,
including those who are able to perform the tasks of a
standardized test of intelligence, is not straightforward.
Even small fine motor impairments might influence test
scores negatively and lead to an underestimation of IQ.
14
Results from timed tests must therefore be interpreted with
care, even for children in GMFCS level I. It is even more
challenging to assess cognition in children with severe
speech and motor impairments.
15
The result is that one-
third of children in GMFCS levels IV and V are assessed,
also in studies aiming to assess a representative sample of
children with CP.
12,16
The challenges of assessing cognition in the severely
affected group leads to cognitive functioning being
assumed. Although a correlation between severity of motor
and cognitive impairments exists, there is no absolute cor-
respondence;
9,11
it is therefore not possible to draw con-
clusions about cognition from functioning in other areas.
Furthermore, it is not necessary as cognition can be
assessed using tests with a multiple-choice format and
allowing for other means of responding than pointing with
a finger. Tests of verbal comprehension, such as the Pea-
body Picture Vocabulary Test
17
and the Test for Recep-
tion of Grammar,
18
and non-verbal reasoning, such as
Raven’s matrices,
19
are suitable for adaptation. Alternative
response modes include gaze pointing and scanning
(Table S1, online supporting information). Comparing
standard and alternative response modes, partner-assisted
©2020 The Authors. Developmental Medicine &Child Neurology published by John Wiley & Sons Ltd on behalf of Mac Keith Press DOI: 10.1111/dmcn.14463 283
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scanning,
20
scanning with switches on a computer,
21
the
use of frames for gaze pointing,
22,23
and gaze pointing on
a computer
20,24–26
have not been found to influence test
results. Despite this, children with the most severe motor
impairments are described as non-assessible, or test results
are provided without information about how tests were
adapted.
27
METHOD
A systematic search of the databases PsycINFO, ERIC, and
MEDLINE (Ovid) was performed on 20th to 22nd Febru-
ary 2019. The terms (cognition OR intelligence) were
sequentially combined with AND (hemipleg* OR unilat-
eral); AND (diplegi*); AND (quadriplegi*); AND (dyski-
netic OR dyskinesia); AND (ataxi*). The search was limited
to human children (0–18y) and papers published in English.
All abstracts of the 525 hits were browsed. Duplicates,
papers not reporting on CP or cognitive functioning,
papers published before 1990 (when the International Clas-
sification of Diseases, 10th Revision was published), papers
where the full text was not available, literature reviews, and
case studies were removed, resulting in 111 hits (35 papers
on hemiplegia, 31 on diplegia, 16 on quadriplegia, 21 on
dyskinesia, and eight on ataxia). Some included information
about more than one subtype, leaving 75 unique hits. Two
papers, about adults, were removed. Eight papers, which
turned up browsing reference lists, were added. From the
remaining 81 papers, information about age and subtypes,
cognitive areas assessed, and main findings were extracted
(Table S2 and Figure S1, online supporting information).
RESULTS
Cognitive impairments can be global (expressed as a low
IQ score) or specific (pertaining to only one cognitive
domain).
Global cognitive impairment
There is wide variability in estimates on the proportion
of children with CP having an IQ less than 70, but
Western countries with national registries report about
30% to 40%.
4,5,9
Spastic quadriplegia, epilepsy, severe
motor impairment, and brain malformations are associ-
ated with more severe cognitive impairments.
7,9,11
Disor-
ders of intellectual development can be considered with
an IQ less than 70, but the diagnostic criteria
2
specifies
that there should also be significant impairment in mas-
tery of everyday activities. Difficulties with the latter
should not be solely attributable to motor impairment,
which complicates the diagnostic process for children in
GMFCS levels III to V as there is a lack of appropriate
tools for assessing adaptive functioning.
28
Further,
although a full-scale IQ score might be below 70, it
would not be advisable to diagnose intellectual disability
if the profile is skewed and functioning is as expected
for age in one or more areas. In the only study differen-
tiating between IQ less than 70 and intellectual disabil-
ity, it was found that although 33% had an IQ less than
70, only 25% qualified for a diagnosis of intellectual dis-
ability.
11
Reporting only IQ and making assumptions
about proportion with intellectual disability on this basis
may lead to an overestimation of the prevalence of intel-
lectual disability in the population with CP.
Giftedness
Children with CP have an increased risk of cognitive
impairments compared with peers, but reporting only this
leaves out an important part of the picture. The find-
ing
11,29
that children with CP can obtain IQ scores above
120 indicates that some are gifted and need follow-up
accordingly.
Unilateral spastic CP
Most children with unilateral CP have normal cognition:
81% to 89% are reported to have an IQ greater than
70.
4,9,11
IQ is not significantly different in children with
left- and right-sided paresis, or in children born preterm
and at term.
30–32
Epilepsy is associated with lower IQ.
32,33
One-third have specific learning impairments,
34
including
impairment in visual–spatial cognition,
35
acquisition of
visual imagery,
36
and executive functioning.
37
The language
functioning in children with right-sided paresis illustrates
the plasticity of the developing brain. Contrary to what
would happen if adults sustained similar focal brain injuries
in the left hemisphere, language is often spared
34
and there
is no difference in verbal IQ between children with left ver-
sus right unilateral brain lesions.
30
However, this right
hemispheric reorganization of language comes with a cost,
as it is associated with lower performance IQ.
38
Bilateral spastic CP: diplegia
Typically, 67% to 78% of children with diplegia are
reported to have an IQ greater than 70.
9,11
When the cause
of diplegia is periventricular leukomalacia (PVL), IQ is
reported to be similar in children born preterm and at
term.
39
However, in children born at term and with varied
aetiology, as few as 39% have an IQ greater than 70.
40
Typically, children with diplegia have a skewed profile
with normal verbal comprehension and impaired visual–
spatial reasoning and non-verbal intelligence.
9,41–44
Even
though this profile can be observed in 3-year-olds,
42
the
difference becomes more pronounced as children enter
school.
45
PVL affects the brain connectivity in the tempo-
ral–parietal cortex,
46
is particularly frequent in children
born preterm,
47
and leads to visual–perceptual impair-
ments.
48
What this paper adds
•Few studies have assessed cognition in a representative sample of children
with cerebral palsy.
•Cognition in children with severe motor impairment is often assumed, not
assessed.
•Lack of assessment may lead to overestimating the prevalence of intellec-
tual disability.
•Lowered cognitive functioning in older children highlights the need for longi-
tudinal studies.
284 Developmental Medicine & Child Neurology 2020, 62: 283–289

The relationships between ophthalmological impair-
ments, the extent of white matter injury, visual–perceptual
impairment, and non-verbal reasoning are difficult to dis-
entangle, and lack of consensus on definition of core con-
cepts and variability in measurement methods makes
comparison across studies challenging. Different concepts,
such as cerebral visual impairment (defined as damage to
or dysfunction of the retrochiasmatic visual pathways
49
)
and visual–perceptual impairment (defined as an impair-
ment in the ability to analyse and process visual informa-
tion
50
), are sometimes used interchangeably, confounding
neurological and functional levels of description.
48
In children with diplegia, visual–perceptual impairments
have been found to be particularly pronounced in those
born preterm.
39
For this group, the degree of visual–per-
ceptual impairment is related to white matter thinning.
51
However, PVL has been found not necessarily to lead to
visual–perceptual impairment.
52
Performance IQ (which
also includes visual–spatial perception, in addition to other
abilities such as non-verbal reasoning and processing
speed) in those born preterm correlates with white matter
integrity.
53
In children born at term, full-scale IQ is
related to white matter integrity and severity of PVL;
39,54
possibly because severe cognitive impairments are more
common and thus full-scale IQ correlates with the extent
of the brain lesions. The presence of ophthalmological
impairments has been reported both to be
39
and not to be
associated with or fully explain visual–perceptual impair-
ment
41,55
or constructional dyspraxia.
43
Visual–spatial impairments and performance IQ are by
far the most studied functions in children with diplegia,
but specific impairments in attention and executive func-
tion have also been reported,
44,56
especially if there is dam-
age to the anterior corpus callosum in addition to other
white matter lesions.
41
Verbal cognition and memory for
verbally presented materials are reported to be as expected
for age.
41
Bilateral spastic CP: quadriplegia
In the subgroup with spasticity there is a correlation
between degree of motor and cognitive impairment, and
up to 90% to 100% with quadriplegia are reported to have
an IQ less than 70.
5,57
However, as formal testing is often
reported to be inaccessible to children with quadriple-
gia,
12,58
this might represent an overestimate of impair-
ment. Studies in which all children were individually
assessed report lower frequencies, around 65%.
9,11
This
implies that there could be more children with quadriple-
gia who have an IQ in the normal range.
9,11,59
Document-
ing the capabilities of children with quadriplegia requires
adapted testing. It has been found that 20% had an IQ
greater than 85,
9
illustrating that severe motor impair-
ments can mask cognitive skills.
Dyskinesia
In this second largest subtype, constituting 6% to 15% of
the total population with CP,
4,12
wide variability in
standardized scores on tests of non-verbal reasoning (20–
129) and verbal comprehension (55–119) is reported.
60,61
Often 50% to 60% are reported to have an IQ less than
70,
4,5,9
but it varies between as few as 25%
11,62
and as
many as 70% to 80%.
8,63
As in spastic CP, normal cogni-
tion is also found in those with the most severe motor
impairments.
64
In children with dyskinetic CP this is to be
expected, as magnetic resonance imaging (MRI) studies
show that lesions in subcortical areas, affecting extrapyra-
midal pathways, are common.
65
Studies of cognition including only children with dyski-
netic CP are rare, but show that visual perception, lan-
guage, memory, and executive functions often are as
expected for age.
60,66
Non-vocal children (i.e. children who
are not able to use speech as mode of communication)
struggle with literacy despite normal cognition.
62
Recently,
executive functioning has been the focus in studies of the
dyskinetic subtype,
29,61
but it has not been confirmed that
they struggle more in this area than those in the subgroup
with spasticity.
11,66
Ataxia
Ataxic CP constitutes around 5% to 6% of the CP
group,
4,9
and 42% to 67% are reported to have an IQ less
than 70.
4,5,8,9
No studies have focused solely on this group,
and knowledge about specific impairments is therefore
lacking.
DISCUSSION
Brain lesions and cognitive functioning
Recent MRI studies, particularly those using diffusion ten-
sor imaging which allows more precise descriptions of
white matter tracts, have advanced our understanding of
the complex relationships between brain lesions and func-
tioning.
27
An acute and severe intrapartum hypoxic–is-
chaemic insult at term has been linked to dyskinetic CP,
while diplegia is often seen in children born preterm with
PVL.
67
However, a lesion is visible on MRI in only 85%
to 90% of children with CP.
47,68
All types of lesion (brain
malformations and white and grey matter lesions) are
found in all subtypes.
47
In children with the same type of
lesion, cognition has been found to vary between normal
and severe intellectual disability.
69
Studies are mixed in
their reporting of correlations between MRI findings and
IQ,
39,40,54
implying that cognitive functioning cannot be
confidently predicted from these scanning technologies.
Acute severe perinatal hypoxia–ischaemia can lead to cog-
nitive deficits and no motor impairments.
67
It is well estab-
lished that in children with unilateral left hemispheric
lesions, language might be reorganized in the right hemi-
sphere and might be their strongest skill.
34,38
However, the
developing brain is vulnerable if the lesion is more exten-
sive. In a study of non-vocal children with bilateral CP,
the language tracts were visualized using diffusion tensor
imaging in the right hemisphere for all five patients
regardless of their level of verbal comprehension, but was
not visible in the left hemisphere for one child without any
Review 285

comprehension of spoken language.
70
Not only the local-
ization and extent of the brain lesion, but also the aetiol-
ogy, must be taken into consideration. When the cause is
cerebral dysgenesis, more have severe cognitive impair-
ments.
11,71
This might possibly be linked to epilepsy: more
children with a cerebral dysgenesis have epilepsy
71
and
epileptiform activity is negatively correlated with intellec-
tual functioning.
11,30
Preterm birth, especially if resulting in infarction, is
associated with CP and a risk of cognitive impairment.
72
However, in children with CP earlier gestational age does
not necessarily imply more cognitive challenges. In bilat-
eral spastic CP, the proportion of individuals with severe
cognitive impairment increased with increasing gestational
age,
73
and also no relation between cognition and gesta-
tional age has been reported.
11
Together, this implies that cognitive functioning cannot
be inferred from MRI findings alone, nor from information
about brain lesion, epilepsy, gestational age at birth, and
motor functioning. Instead, the initial brain lesion can be
viewed as a constraint on development. Cognitive impair-
ments are the result of reciprocal and continuing interac-
tions between the child and their environment, influenced
by the child’s opportunities for active exploration and par-
ticipation.
74
Knowledge about the risk factors is important
because it can lead to awareness about the need for assess-
ment and interventions, and aid in developing follow-up
programmes.
75
Developmental trends
The panorama of CP has changed over recent decades,
with a lower prevalence, proportion of children developing
bilateral spastic CP, and incidence of intellectual disabil-
ity.
76
However, knowledge about the developmental trajec-
tories of cognition in children with CP is less clear, as
there are few longitudinal studies. Of the 81 identified
studies included in this review, only nine had a longitudi-
nal design.
12,13,30,39,42,45,77–79
These studies show that measures of cognitive function-
ing at 12 and 18 months of age correlate,
77
that the skewed
cognitive profile of school-aged children with spastic bilat-
eral CP is observable from 3 years of age,
42
and that after
entering school there is an increase in verbal IQ so that it
becomes age-average while performance IQ continues to
be in the low range.
45,79
There is a differential develop-
ment of non-verbal reasoning capacity in children in differ-
ent GMFCS levels: children in level V not only show
initial lower functioning but also increase less with devel-
opment.
12
For children with unilateral CP, IQ was stable
from 3 to 5 years of age,
30
while children with the most
severe speech and motor impairments did not show the
expected increase in non-verbal reasoning from 6 to 12
years of age despite normal cognition.
78
The development
of expressive communication is related to the type of
motor impairment, whereas receptive communication is
related to IQ.
13
Following children born preterm and at
term, significantly more children with spastic diplegia born
preterm were found to develop visual–perceptual impair-
ments.
39
Developmental model
The most troubling finding is the lack of age-expected
increases in cognitive development in children with severe
speech and motor impairments.
78
This might be explained
by the brain lesion, but children with motor impairments
also have different experiential backgrounds compared with
those who are not restricted in their locomotion. In chil-
dren restricted in their locomotion, both localization of a
brain lesion and restricted upper-limb functioning explain
why action-based visual perception is more demanding
than object-based perception.
80
In children expressing
themselves using aided communication, their instructions
on a construction task included little information about
sizes and spatial relations,
81
further suggesting that allo-
centric strategies are particularly challenging for severely
motor-impaired children. An interaction between the brain
lesion and lack of appropriate experiences seems likely.
74
Applying an embodied cognition framework, the ‘mind
must be understood in the context of its relationship to a
physical body that interacts with the world’.
82
Findings
supporting this position are that: (1) action planning,
which implies that we consider the end point of a move-
ment from the start, is challenging for children with CP
and does not improve with age as would be expected;
83
(2)
finger gnosis is important for early numeracy skills, imply-
ing that the use of hands, the understanding of numbers,
and the perception of space are related;
84
and (3) construc-
tional dyspraxia in children with CP cannot be related to
visual and visual–perceptual impairments.
43
Thus, the con-
sequences of an initial impairment might be ‘wide reaching
with cascading developmental effect on other abilities’,
85
if
measures are not put in place to counteract and minimize
the developmental consequences.
Interventions for children with cognitive impairments
It is well established that early interventions are beneficial
for alleviating motor impairments in children with CP, but
the effect of cognitive training has scarcely been studied.
86
Also, most studies aim at improving literacy, despite
visual–spatial and attentional impairments being more fre-
quent than language impairments.
27
In a study of executive
functioning, no effect of training was found.
87
This does
not imply that one should do nothing. Children with CP
attending mainstream school had significantly better pro-
gress in mathematics and reading than those attending a
special school, despite identical verbal IQ. The finding that
the groups differed in the amount of the teaching received,
with the children in the mainstream school receiving 1.7
times more, emphasizes the importance of interven-
tions.
88,89
For the non-vocal group, it is imperative to pro-
vide augmentative and alternative communication as early
as possible. Otherwise they might be seriously hampered in
their development of communication and language and
286 Developmental Medicine & Child Neurology 2020, 62: 283–289

have severely restricted opportunities for interaction and
participation,
90
which in turn might have negative cascad-
ing effects on their social, academic, emotional, and cogni-
tive development.
CONCLUSION
There is a wealth of studies on motor functioning in chil-
dren with CP. However, even though parents report that
learning difficulties are at least as challenging and cogni-
tion plays a greater role for communication, academic
functioning, participation, and social functioning, it has
been less focused upon.
59,91
This review illustrates that there are gaps to be filled;
few studies have assessed cognitive profiles in a large repre-
sentative population of children with CP, including also
very young children and those with the most severe speech
and motor impairments, and there is a need for longitudi-
nal and intervention studies. Some areas, such as visual–
spatial abilities and language, are much more focused on,
while others, such as memory, are less well researched.
This might be because the few studies on memory have
not reported specific challenges;
41,44
however, as these
studies only include children with milder motor impair-
ments, further research seems warranted.
There seems to be an increasing focus on finding associ-
ations between extent and localization of brain lesions and
cognitive functions; however, given the evidence of early
plasticity as well as the heterogeneity of cognitive function-
ing in children with similar MRI lesions, it might be ques-
tioned whether this is the most useful path forwards. The
interplay between brain lesions, sensory deficits, experien-
tial opportunities, and cognitive functioning is complex. It
has been investigated whether developmental disregard in
children with hemiplegia, a neglect-like disregard of their
affected upper limb, is the result of injury to neural net-
works involved in spatial attention, which are connected to
areas involved in motor planning, or the result of lack of
use of affected hands during important developmental peri-
ods. Monitoring event-related potential during task perfor-
mance, specific impairments in executive functioning were
not found, but general difficulties with performing were.
This implied that the executive control processes preceding
the motor response were affected, requiring an enhanced
cognitive effort in goal-directed behaviour and a develop-
mental delay of executive control mechanisms.
92
The same
complexity is found when investigating the relationships
between visual perception and cognition. Visual–perceptual
impairment has been reported to be associated with lower
cognitive functioning, found in children with normal cog-
nition, and unrelated to non-verbal cognitive function-
ing.
52,93,94
Future studies of cognitive development and the effect
of interventions should therefore take the complex inter-
play over time between body, brain, and mind into
account. Tests need to be adapted, for example using eye-
gaze technologies, so that cognitive functioning can be
reliably assessed, and not only assumed, in the most
severely motor-impaired children.
20,24–26
In the future,
brain–computer interfaces might gain importance both for
assessment and interventions.
95
Furthermore, it might be
that not only traditional neuropsychological tests and com-
puterized training tasks, but more naturalistic tests and
tasks increasing real-life abilities, such as goal-setting and
planning abilities, are needed.
SUPPORTING INFORMATION
The following additional material may be found online:
Table S1: Review of studies of adapted assessment of cogni-
tion.
Table S2: Eighty-one studies of cognitive functioning in chil-
dren with cerebral palsy.
Figure S1: PRISMA 2009 flow diagram.
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