What is cerebral palsy?

Many publications attempt to define CP (see for example Refs. ). Definition is defined as a precise statement of the essential nature of a thing and the clear determination of the limits of anything . A definition should therefore describe what a thing is and what it is not, precisely and clearly. No publication has yet achieved this, but there is agreement that CP is an “umbrella term” covering a wide variety of clinical conditions that meet 4 criteria:

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  Presence of a disorder of movement or posture

  
  
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  Secondary to a cerebral abnormality

  
  
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  Arising early in development

  
  
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  By the time movement impairment exists, the cerebral abnormality is static.

There is no test, genetic, metabolic, immunologic, or otherwise, that demonstrates the existence or absence of CP because there is no specified cause, cerebral pathology, or even type of motor impairment—only that motor impairment exists resulting from nonprogressive cerebral pathology acquired early in life. It is not a single disease. Even as a clinical description these criteria fail in several aspects to achieve the precision required of a definition, such as specifying the age at which development is no longer considered “early.” There is no agreement on this age, but most surveillance systems distinguish cases in which motor impairment is obviously acquired postneonatally, typically following cerebral infection or head trauma. Because it is difficult to definitively differentiate between pre- and neonatally acquired brain damage, all those not postneonatally acquired are usually considered together.

The 4 criteria cannot be addressed until (a) motor development can be clearly recognized as being normal or disordered, and (b) the possibility of progressive cerebral disease can be excluded. Signs suggesting disordered motor control may be recognized very early in life, but accurate prediction has only been confirmed by trained observers in the small proportion of persons with CP born very preterm. Acquisition of the cerebral abnormality may precede recognition of the motor disorder by many months or even years. However, brain-impaired infants, particularly the most severely impaired, are at increased risk of dying before reaching an age at which the criteria for CP can be confirmed. Early death is a competing outcome. On the other hand, it is difficult to definitively exclude the possibility of progression or resolution at any age. Even if cerebral pathology is static, motor abilities change in all children over time, even if that development is grossly abnormal, making functional change an unreliable marker for progressive cerebral pathology. Conversely, a proportion of children described as CP at an early age catch up with their normally developing peers at a later age and the CP label is withdrawn. Therefore, the choice of an age that must be attained before being counted as CP, as well as the age beyond which development is no longer early , is arbitrary and depends on the interest in using the CP label. Treating clinicians are more flexible in applying the CP label, because their primary concern is to balance the psychological effects of labeling a child as having CP with the therapeutic opportunities that the label can afford. This balance can change with time. For example, the increasing frequency of children labeled as having CP of minimal severity in Western Australia is attributed to approval of botulinum toxin therapy for the release of hypertonia in lower limbs, but only for those labeled as CP. Before the availability of this therapy, there was little advantage for a minimally impaired toe walker to be labeled as CP.

By contrast, those responsible for population-based CP registers or surveillance systems need to know exactly whom to count. The compilers adhere strictly to self-imposed limits chosen to facilitate reliability over time and between observers contributing to their database. However, different registers face different problems. Registers with a long life span require primarily a constant definition over time, and this was the guiding principle of the recommendation by Badawi and colleagues that conditions historically excluded from CP (not “diagnosed” as CP on account of having another diagnosis) continue to be excluded, even if meeting the criteria for CP. By contrast, reliability between current observers is the guiding principle of the more recent multicenter surveillance system in Europe, which adopted a flow chart driven by dichotomous responses. The reality of barriers to achieving interobserver agreement of classification is demonstrated by the relatively poor agreement achieved with this flow chart, even when initial observations were standardized by presenting classifiers with written descriptions.