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The cerebral palsies (CP) are a heterogeneous group of non-progressive motor disorders of the developing brain. By convention, brain injuries occurring at any stage antenatally and postnatally to the age of 2 years are included in the definition of CP. Primary disorders of the spinal cord such as neural tube defects, neuropathies, and myopathies are excluded. Cerebral palsy should be viewed as part of a “continuum of reproductive casualty”,1 comprising miscarriages, stillbirths, and severe and minor brain injuries. Consequently, the incidence and causes of CP are a matter of great interest since they provide a benchmark of reproductive health.
The incidence of CP in developed countries is stable at about 2–2.5/1000 live births. The risk of CP for premature babies is 5–80/1000 live births, though the majority of cases of CP are term born babies (fig 1).
Cerebral palsy rates and numbers (excluding cases due to postneonatal causes) by gestational age and year of birth in Western Australia, 1981 to 1992. Prematurity is defined as birth below 37 weeks gestation. Note that although the rate of CP is higher for the preterm baby per thousand live births (lines), term births account for the majority of cases of CP (histograms). Modified from Stanley et al,31 by permission of MacKeith Press.
PATHOLOGY
There are many ways of classifying CP, but the simplest is according to number and distribution of affected limbs: monoplegia, hemiplegia, diplegia, triplegia, and quadriplegia. As a rule, hemiplegia is associated with late third trimester injuries. By contrast, the risk of bilateral brain injury increases with prematurity. The various means of classifying the cerebral palsies are summarised in table 1. The modified Swedish classification shown in table 2 is most used because of its simplicity. The relation between gestational age and CP phenotype is well established (table 3). …