How is cerebral palsy defined?
Despite general consensus about the broader concepts outlined in previous definitions of cerebral palsy, in 2004 an International Workshop on Definition and Classification of Cerebral Palsy held in Bethesda, Maryland, undertook the task of updating the definition. The definition accepted by the Workshop describes cerebral palsy as: ‘a group of permanent disorders of the development of movement and posture, causing activity limitation, that are attributed to non-progressive disturbances that occurred in the developing fetal or infant brain. The motor disorders of cerebral palsy are often accompanied by disturbances of sensation, perception, cognition, communication, behaviour, by epilepsy and by secondary musculoskeletal problems’.
The key concepts are that cerebral palsy is not one condition but is a label or clinical diagnosis that is applied to persons with a movement disorder as a result of a number of different types of maldevelopment or injury to the brain. The brain abnormality must have occurred early in life and be considered to be non-progressive. In Australia, brain injury acquired before the age of two years is included under the cerebral palsy label.
Reports from developed countries suggest that the birth cohort prevalence of cerebral palsy is approximately two per 1000 live births, although there is some variability. That means that about two infants in every 1000 born in any defined geographical area will be later diagnosed as having cerebral palsy.
Trends in the rates of cerebral palsy are of considerable interest as they are often used as an indicator of the effectiveness of preventative or intervention strategies. Some reports have indicated that the overall birth prevalence of cerebral palsy remained fairly stable up until the early 1990s, whilst others have suggested a general rise throughout the 1980s. This rise has been widely considered to be due to increased survival rates of extremely preterm infants (infants born earlier than 28th week of pregnancy) that was not paralleled by improvement in their outcomes.
In Victoria, we have been able to show that the prevalence of cerebral palsy has most likely been declining since the late 1990s (see graph). This Victorian research provides ‘real-world’ support for the effectiveness of strategies aimed at protecting the brain from injury and continual innovation in management of premature or sick newborns.
At present, a diagnosis of cerebral palsy is based on the identification of a collection of symptoms, signs, and sometimes historical information. The main classifications used to describe cerebral palsy reflect the definitional emphasis on impairment of movement. Although there is no universally accepted international standard, the most commonly used classification includes a description of both the type of motor (movement) disorder and its topographical pattern, for example, spastic quadriplegia. This is often referred to as the clinical or cerebral palsy subtype.
Motor types in cerebral palsy comprise spasticity, dystonia, choreo-athetosis, ataxia, and hypotonia Spasticity is defined as resistance to passive movement that increases with increasing speed of stretch and varies with direction of movement. Dyskinetic cerebral palsy (dystonia and choreo-athetosis) is characterised by involuntary, sustained or intermittent muscle contraction that causes twisting and/or repetitive movements or abnormal postures. In ataxic cerebral palsy there is loss of orderly muscle contraction such that movements are performed with abnormal force, rhythm, or accuracy. Hypotonia, defined as abnormally low muscle tone, is included as an additional type of cerebral palsy in Australia.
Mixed motor types are common in cerebral palsy and usually the predominant type is used. Approximately 80-90% of children have a predominantly spastic motor type. Three commonly occurring topographical patterns of spasticity are used - quadriplegia (or tetraplegia in some countries), diplegia, and hemiplegia. Spastic quadriplegia is defined as involvement of all four limbs with the upper limbs affected as least as much as the lower limbs. In spastic diplegia, the lower limbs are involved more than the upper limbs. Spastic hemiplegia describes unilateral involvement. Additional terms such as monoplegia and triplegia are often used to describe the involvement of one or three limbs respectively. The distribution of topographical patterns of spasticity in Victoria is shown below;
Gross motor function in cerebral palsy is now almost universally described using the Gross Motor Function Classification System (GMFCS), a classification of the child’s usual method of mobility across five different age groups. Please click on the link for a description of GMFCS levels for children aged 6-12 years: http://www.rch.org.au/uploadedFiles/Main/Content/ortho/GMFCSER_6-12.pdf
Other classifications used to describe cerebral palsy in Victoria include:
- Manual Ability Classification System (MACS)
- Functional Mobility Scale (FMS)
- Communication Function Classification System (CFCS)
- Viking speech scale
- Eating and Drinking Ability Classification System (EDACS)
- MRI classification