Objective: To describe the trends for and severity of dyskinetic cerebral palsy in a European collaborative study between cerebral palsy registers, the Surveillance of Cerebral Palsy in Europe (SCPE).
Methods: The prevalence of dyskinetic cerebral palsy was calculated in children born in 1976–1996. Walking ability, accompanying impairments and perinatal adverse events were analysed.
Results: 578 children had dyskinetic cerebral palsy, of whom 70% were born at term. The prevalence per 1000 live births increased from 0.08 in the 1970s to 0.14 in the 1990s. For the 386 children (70%) with a birth weight of ⩾2500 g, the increase was significant (0.05 to 0.12). There was a concurrent decrease in neonatal mortality among children with a birth weight of ⩾2500 g. Overall, 16% of the children walked without aids, 24% with aids and 59% needed a wheelchair. Severe learning disability was present in 52%, epilepsy in 51% and severe visual and hearing impairment in 19% and 6%, respectively. Accompanying impairments increased with motor severity. In children born in 1991–1996, perinatal adverse events, that is an Apgar score of <5 at 5 min and convulsions before 72 h, had occurred more frequently compared with children with bilateral spastic cerebral palsy (BSCP, n = 4746). Children with dyskinetic cerebral palsy had more severe cognitive and motor impairments than children with BSCP.
Conclusions: The prevalence of dyskinetic cerebral palsy appears to have increased in children with a normal birth weight. They have frequently experienced perinatal adverse events. Most children have a severe motor impairment and several accompanying impairments.
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Dyskinetic cerebral palsy is one of the most disabling forms of cerebral palsy. In the past 10 years, the prevalence of cerebral palsy in Europe has remained at a rate of approximately two in every 1000 live births.1 Spastic cerebral palsy, characterised by a velocity-dependent rise in muscle tone, distributed uni- or bilaterally, is the most common form, while dyskinetic cerebral palsy varies most in terms of prevalence between different cerebral palsy registers. In Northern Ireland, it accounted for 3% of children with cerebral palsy born in 1977–1997,2 while in a Swedish report it accounted for 15% of cerebral palsies in children born in 1995–1998.3 4 In other recent studies from Norway5 and Turkey,6 the percentages were 6% and 6.4%, respectively. These differences may be explained by varying diagnostic routines. In some countries, the co-existence of spastic and dyskinetic signs always leads to a diagnosis of spastic cerebral palsy, while in others the dominant symptom provides the basis for diagnosis, that is children with dyskinesia in the form of choreo-athetosis and/or dystonia as the disabling movement disorder irrespective of added signs of spasticity are diagnosed as having dyskinetic cerebral palsy. The latter principle is now proposed by the Surveillance of Cerebral Palsy in Europe (SCPE) collaboration7 and the International Workshop on the Definition and Classification of Cerebral Palsy.8 Dyskinetic cerebral palsy is characterised by abnormal patterns of posture and/or movement (dystonic subgroup), accompanied by involuntary, uncontrolled, recurring and occasionally stereotyped movements (choreo-athetotic subgroup),9 while spastic cerebral palsy is characterised by a velocity-dependent rise in muscle tone, subgrouped by the distribution of the symptoms into uni- or bilateral spastic cerebral palsy (BSCP).7 However, differentiating between dystonia and spasticity may be a challenge in some cases.10 The motor impairment is often, but not always, severe. Speech is often hampered, necessitating alternative and augmentative communication, and postnatal growth is often retarded.4
What is already known on this topic
Dyskinetic cerebral palsy is one of the most severe forms of cerebral palsy.
It is characterised by involuntary movements and changes in muscle tone.
Dyskinetic cerebral palsy is most common in children born at term who have experienced adverse perinatal events.
What this study adds
This is the first multicentre study of dyskinetic cerebral palsy to analyse trends in prevalence and severity in a large sample.
An increase in prevalence has been detected.
Dyskinetic cerebral palsy differs from other types of cerebral palsy as regards background and clinical features and is associated with a larger impairment load.
Kyllerman et al described 116 children with dyskinetic cerebral palsy born in 1959–1970, 35% of whom were born preterm.11 The main aetiological factors were found to be perinatal in two thirds of the children and prenatal in approximately one in five. In a recent Swedish study, the majority were born at full term, had experienced perinatal adverse events and had neuroimaging findings supporting a perinatal aetiology.4
Modern neuroimaging in the form of magnetic resonance imaging has improved our ability to visualise and date the brain lesions in cerebral palsy, which, in dyskinetic cerebral palsy, are typically located in the basal ganglia and thalamus, often found after a perinatal hypoxic–ischaemic event or neonatal shock in a child born at term or near term.12 13 14
SCPE is the largest international collaborative study between cerebral palsy registers and surveys in the world.15 It currently comprises 16 registers from nine countries across Europe.
The aim of this study was to analyse trends in prevalence, describe the severity of motor disability and accompanying impairments in children with dyskinetic cerebral palsy from the SCPE collaboration and compare them with children with the more common BSCP.
This was a multi-centre collaborative study comprising children with cerebral palsy born in 1976–1996. A total of 4 336 716 births were recorded in the area covered by the registers. Children with dyskinetic cerebral palsy were included if they were born in the area, with the exception of centre 1, where cases born outside but living in the area were also included. The inclusion process is illustrated in fig 1. Post-neonatal cases were excluded. All children within the dataset had a diagnosis of cerebral palsy confirmed at 5 years of age and were registered in the local cerebral palsy register before data were transmitted to the SCPE common database. Details relating to these methods have previously been reported.15 The centres contributed cerebral palsy cases over different time periods (table 1).
Birth weight was recorded and compared with standard growth curves. For Swedish children, the Källén neonatal standard curves were used,16 while the Tin neonatal standard curves were used for all other children.16 17 18 Small for gestational age was defined as a birth weight below –2 SD.
The prevalence rate was calculated separately for children with birth weights of <2500 g and ⩾2500 g. Due to missing information, the prevalence rates by gestational age produced less reliable figures.
Severe motor impairment was defined as needing a wheelchair, moderate as ambulation with aids and mild as ambulation without aids.
Severe mental retardation/learning disability was defined as having an IQ below 50. A history of two unprovoked seizures, excluding febrile or neonatal seizures, was defined as epilepsy. Severe visual impairment was defined as a visual acuity of <6/60 (Snellen scale) or 0.1 (decimal scale) in both eyes, while severe hearing impairment was defined as a loss of >70 dB in the better ear.
Perinatal adverse events were defined as the occurrence of neonatal convulsions and an Apgar score of <5 at 5 min. Due to missing information in the earlier birth years in this dataset, children with dyskinetic cerebral palsy born in 1991–1996 were chosen for comparison with children with BSCP from the same birth years (post-neonatal cases excluded). To exclude the effects of pure immaturity in preterm children, only the subgroups of children born near term and at term, that is after 34 completed weeks, were analysed and compared with respect to perinatal adverse events. A comparison with 4746 children with BSCP, identified from the same centres, was carried out regarding motor function, accompanying impairments and, in the term and near term children born in 1991–1996, the occurrence of neonatal convulsions and an Apgar score of <5 at 5 min. Overall, 2149 children were born near term or at term in the BSCP group.
Crude prevalence was calculated and expressed by 1000 live births. Spearman’s correlation was used. The χ2 test was used for comparisons of groups. The χ2 trend in proportion test was used for trends. Mean z scores of birth weights were calculated by gestational age groups, gender and birth-year period.
Modelling, that is grouped logistic regression, was used to test centre and birth-year effects. Trend analysis results are provided from pooled data, adjusted for centre effect if any and only if there was no significant birth-year–centre interaction (p>0.005).
In overall terms, there was a non-significant tendency towards an increase in the prevalence rate (p = 0.017) of dyskinetic cerebral palsy. In children with a birth weight of ⩾2500 g, constituting 70% of all subjects, the prevalence rate increased significantly, from about 0.05 to 0.12 (p<0.001) (fig 2), while the prevalence rate for those with a birth weight of <2500 g did not (p = 0.20). During the same period, neonatal mortality decreased significantly at almost all the participating centres, from more than 10 to about 3.7 per 1000 live births (fig 3). This was primarily due to increased survival in preterm children, but there was also a significant decrease in the neonatal mortality of children with a birth weight of ⩾2500 g (p<0.001). The prevalence of BSCP in children of normal birth weight did not increase or decrease during the time period (p = 0.94) (fig 4).
Of 578 children with dyskinetic cerebral palsy, 343 (59%) were boys. Data on gestational age were available in 544: 22 (4%) were born before 28 completed weeks of gestation, 63 (12%) at 28–31 weeks, 79 (15%) at 32–36 weeks and 380 (70%) after 37 completed weeks of gestation. The percentage of children with dyskinetic cerebral palsy born at term increased significantly from 63% to 86% during the 1990s (χ2trend = 4898, p<0.05).
Data on birth weight were available in 550 cases. The birth weight was <1000 g in 17 (3%), 1000–1499 g in 53 (10%), 1500–2499 g in 94 (17%) and ⩾2500 g in 386 (70%). Of these 386, 350 children (91%) with a birth weight of ⩾2500 g were known to have been born at term. Small for gestational age was detected in 27 children (5%), which was significantly more than expected (p<0.001); 19 of these children were born at term and 16 of these 19 were boys. The number of births had been recorded in 543 cases: 30 children were one of twins, two were one of triplets and 511 (94%) were singletons.
Walking ability was reported in 555 cases. Ninety one children (16%) walked without aids, 135 (24%) with aids and 329 (59%) were confined to wheelchair ambulation. The distribution of motor ability by birth year is shown in fig 5, expressed as prevalence. The distribution of walking ability did not differ between term and preterm groups (χ2 = 0.70, NS) or between boys and girls (χ2 = 3.5, NS). Nor was there any trend in walking ability by birth year. In the BSCP group, 36% of children walked unaided, while 42% were unable to walk.
Severe learning disability was present in 245 of 474 (52%) in the dyskinetic group compared with 33% in the BSCP group (p<0.001). The occurrence of severe learning disability was similar in children with mild or severe motor impairment, while in children with moderate motor impairment, a higher percentage of children with dyskinetic cerebral palsy had severe learning disability (p<0.01). A history of epilepsy was recorded in 265 (51%) compared with 62% with BSCP, while 51 of 476 (11%) had hearing impairment, which was severe in 28 (6%). Severe hearing impairment was more uncommon in the BSCP group (3%). Visual impairment was present in 242 (45%) and was severe in 101 (19%). Visual impairment was recorded in 45% of the children with BSCP, and was severe in 38%.
The percentage of children with severe learning disability, epilepsy, severe hearing impairment and severe visual impairment increased with motor severity (p<0.01) (fig 6). Of 460 children, 199 (43%) had severe learning disability and were unable to walk, thus meeting the SCPE criteria for severe cerebral palsy.
Perinatal adverse events
In the birth years 1991–1996, 148 children were born at term or near term with dyskinetic cerebral palsy. Information about perinatal convulsions was available in 94 children and 51 (76%) had convulsions before 3 days of age, while, in children with BSCP, convulsions were present in 32% (p<0.001). The Apgar score at 5 min was known in 92 children, 33 (43%) of whom had an Apgar score of <5 at 5 min. In children with BSCP, 15% had an Apgar score of <5 at 5 min (p<0.001). In the dyskinetic group, 84 children of 145 (58%) had severe motor impairment compared with 43% in the BSCP group (p<0.01).
The database of the SCPE network offers a unique opportunity to study trends over time in cerebral palsy subtypes with a low prevalence, the numbers of which are very small in national registers when classified by birthweight groups per birth years. Dyskinetic cerebral palsy is one such subtype accounting for around 10% or less of the entire cerebral palsy population.1 2 3 4 5 6 There is evidence that it occurs mainly in children born at term and is related to adverse perinatal events,4 11 14 but trends over time are inconsistent, most probably due to the problem of small numbers mentioned above. In contrast to reports for other types of cerebral palsy, for example BSCP,19 and cerebral palsy in low gestational age groups,20 there was no evidence of a decreasing trend. Instead, there was an overall trend towards an increase from 0.08 to 0.12 during the study period. This was due to a significant increase in the children with a normal birth weight (from about 0.05 to 0.12), of whom more than 90% were born at term, a group in which there was a concurrent decrease in neonatal mortality. In the total dyskinetic population, the majority of the children were born at term and the percentage increased during the 1990s. The most recent data in this study are from children born in 1996, and whether these trends hold is yet to be investigated.
It is unlikely that the rise in the dyskinetic cerebral palsy rate simply reflects a change in classifying routines, as there was neither a concomitant increase in dyskinetic cerebral palsy in the preterm nor a decrease in BSCP in the term children (the subtype to which children could have been more frequently allocated previously). However, the study of the epidemiology of dyskinetic cerebral palsy is particularly challenging, given the varying definitions and diagnostic practices at the participating centres, which did not significantly change during these years. The diagnostic decision tree and consensus of the SCPE, together with the Reference and Training Manual,1 9 15 will facilitate future analyses using this dataset, which will then be based upon even more harmonised data from an increasingly large area of Europe.
Over the years, there have been changes in the aetiological spectrum of dyskinetic cerebral palsy. In Swedish children born in the 1960s, hyperbilirubinaemia was present as a contributory factor in one third of cases,11 while it is now a rare factor in the developed world. One well-known aetiological factor in dyskinetic cerebral palsy which has remained constant is hypoxic–ischaemic encephalopathy in infants born at term or near term.4 The possible pathophysiology in these cases has been well described,21 as well as the typical location of the lesions.13 When compared with children with BSCP in the database, perinatal adverse events such as low Apgar scores and neonatal convulsions were significantly more common in dyskinetic cerebral palsy. A higher risk of cerebral palsy in children born at term after low Apgar scores has been reported by Moster et al, among others.22 Clustering of neonatal seizures and low Apgar scores in children born at term, possible indicators of neonatal encephalopathy,23 24 were frequent findings in our study. Badawi et al found that survivors of neonatal encephalopathy with cerebral palsy had more severe motor impairment and more frequent cognitive impairment and epilepsy than children with cerebral palsy without neonatal encephalopathy.25 These findings were corroborated by our study.
Being small or large for gestational age is also frequently reported as a contributory factor in this and other types of cerebral palsy. Because of the varying quality of the data in such a multicentre study,26 conclusions should be drawn with care. However, using a strategy developed by Jarvis et al,18 the percentage of small for gestational age in children with dyskinetic cerebral palsy was higher than expected in the population.
Dyskinetic cerebral palsy is particularly disabling compared with BSCP, the largest cerebral palsy subtype. Almost 60% used a wheelchair for ambulation, which was significantly more common than in children with BSCP. More than half had accompanying impairments and disabilities, such as severe learning disability and epilepsy. The more severe the motor impairment, the larger the percentage of accompanying impairments. This is in accordance with other studies5 27 and is also supported by neuroimaging studies showing that more severe motor problems were associated not only with more extensive brain lesions but also with cognitive and other accompanying impairments, such as visual impairment and swallowing difficulties.14 The number fulfilling the criteria for severe cerebral palsy according to SCPE was larger than that reported in other studies when considering the total cerebral palsy population.1 27
From the present study, we can conclude that the prevalence of dyskinetic cerebral palsy, which occurs mostly in near-term or term children with a birth weight of ⩾2500 g, appears to be increasing. Children with dyskinetic cerebral palsy have more severe motor impairment than children with types of other cerebral palsy and the percentage with learning disability, epilepsy, visual and hearing impairments increases with the severity of the motor impairment. Perinatal adverse events tend to be more common in dyskinetic cerebral palsy than in other types of cerebral palsy.
SCPE participants: C Cans, S Rey (RHEOP, Grenoble, France); C Arnaud (INSERM CJF, Toulouse, France); J Chalmers (ISDSHS, Edinburgh, UK); V McManus, A Lyons (Lavanagh Centre, Cork, Ireland); J Parkes, H Dolk (Belfast, UK); P Uvebrant, K Himmelmann (Gothenburg University, Göteborg, Sweden); O Hensey, V Dowding (Central Remedial Clinic, Dublin, Ireland); A Colver (University of Newcastle, Newcastle, UK); J Kurinczuk, G Surman (NPEU, Oxford, UK); I Krägeloh-Mann, V Horber (Tübingen University, Tübingen, Germany); MJ Platt (University of Liverpool, Liverpool, UK); P Udall, S Holst-Ravn (NIPH, Copenhagen, Denmark); MG Torrioli, S Matricardi (Lazio Cerebral Palsy Register, Rome, Italy); G Andersen, A Meberg (CPRN, Tonsberg, Norway); M Bottos (Bologna, Italy); G Gaffney (Galway, Ireland). Preliminary work on this paper was carried out by Dr David Coghlan.
Funding This study was supported by European Commission funds: DGXII-BIOMED2-Contract no. BMH4-983701; DGXII-FP5-Contract No. QLG5-CT-2001-30133; DG SANCO Contract no. 20033131.
Competing interests None.
Provenance and peer review Not commissioned; externally peer reviewed.
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