Etiology and Pathogenesis

CP can arise from many different causes and is often multifactorial. The majority of children with CP have brain lesions arising prenatally or in the perinatal period. Approximately 15% of causes occur in the neonatal period or early in childhood. There is no consensus for an upper age limit when brain injury would no longer cause symptoms classified as CP. Although research groups sometimes set a maximum age of brain injury ranging from 2 to 5 years, such cutoffs are less important in clinical practice.

The most important prenatal and perinatal risk factors associated with CP are prematurity and low birth weight. About half of new cases of CP occur in children born weighing less than 1000 g. Intracranial hemorrhage, intrauterine growth retardation, and placental pathology are associated with higher rates of CP. Increasingly, infection (including maternal chorioamnionitis) and stroke have been recognized as contributors. Multiple pregnancy increases the risk for CP, with higher risk conferred with each multiple. Less common factors include congenital abnormalities, such as brain malformation and genetic disorders. In the past, many cases of CP were attributed to birth asphyxia. Although perinatal hypoxia or ischemia may be present in up to 15% of children with later CP, it is now thought that only a small number of cases are attributable to this alone. In fact, other pathologies are identified in more than 95% of cases of CP.

Causes of CP occurring after birth include infection, neonatal stroke, hypoxic brain injury, traumatic brain injury, and kernicterus. Infection may cause CP either through sepsis leading to secondary brain hypoperfusion or through direct central nervous system (CNS) infection. Kernicterus is the sequelae of severe hyperbilirubinemia; this typically causes a choreoathetoid movement disorder in conjunction with gaze abnormalities and hearing impairment.

Clinical Presentation

Some children with CP have recognized risk factors (e.g., prematurity and low birth weight) leading to early neurologic and developmental screening. In these children, follow-up visits or early intervention evaluations should include serial assessments of tone and motor development. In the first few months, early signs may include low tone or decreased movements in affected limbs (Figure 77-1). However, not all such clinical presentations progress to CP. Although severe CP may be evident in the first months of life, it is generally difficult to make a definitive diagnosis before 1 year of age. Some clinicians advise not giving the diagnosis to a child younger than 2 years of age. This is because many children identified as having tone or motor abnormalities before 12 months of age will be free of symptoms by school age. Caution is necessary to avoid overdiagnosis in infancy.

Figure 77-1 Cerebral palsy.

In children without recognized risk factors, CP most often presents as delayed motor development. In the first year, this may manifest as difficulty with use of an affected limb. Some children are identified when “toe walking” becomes obvious as toddlers. Delay in reaching gross and fine motor milestones or early asymmetry in limb posture or use should prompt consideration of CP in the differential diagnosis.

In all children with CP, a careful history must confirm a nonprogressive course. The pregnancy and birth history are particularly important in eliciting possible etiologies. If the child was born prematurely or received intensive care as a neonate, specific details should be obtained. Reports of any prior neuroimaging should be obtained. The clinician should assess for other factors causing functional impairment that may mimic motor dysfunction, such as musculoskeletal or sensory difficulties. Current medications must be inventoried, particularly any sedating medications that might affect tone or motor activity at the time of examination. A developmental history is useful in recognizing the trajectory of development, as well as whether nonmotor delays coexist. A family history of neurologic disease should raise suspicion for the possibility of a genetic or metabolic process.

It can be helpful to classify CP by the type and distribution of motor impairment. There is no universally recognized set of categories, and some providers may subtype CP by more specific features, severity, and etiology (when known). Overlap may occur, with at least 10% of cases considered “mixed” CP. Nonetheless, the history and physical examination allow the clinician to classify CP into the broad categories described here.

Spastic Cerebral Palsy

Spastic CP is the most common type, comprising about 70% of cases. It may be further subdivided according to the pattern of limb involvement. Spastic diplegia primarily involves the lower limbs and may be symmetric or asymmetric (see Figure 77-1). Parents often give a history of “tiptoeing” even when walking holding on to furniture. Spastic hemiparesis involves the upper and lower limb on one side, usually with the upper extremity more affected than the lower (see Figure 77-1). Parents may report early handedness (before 2 years) or that the child did not support his or her weight as well on the affected side when crawling. Spastic quadriparesis evenly involves all four limbs (see Figure 77-1).

In the clinical history, patients with spastic CP are more likely to have been at risk for a cortical brain injury. Certain types of spastic CP are more highly associated with certain risks for brain injury. Children with spastic diplegia have likely had injury to both cerebral hemispheres; this most often is periventricular leukomalacia related to premature birth. Children with spastic hemiparesis more likely had unilateral injury, such as prenatal or perinatal stroke. Risk factors for stroke, such as a family history of hypercoagulability, should be assessed. Children with spastic quadriparesis may be the most severely affected. Global brain injury has often occurred, and there is a higher rate of associated cognitive impairment, epilepsy, and other disabilities.

Spastic CP is characterized on physical examination by signs of an upper motor neuron syndrome, indicating a CNS process. On observation, the clinician may see a characteristic pattern in spastic limbs (Figure 77-2). Affected upper extremities have a tendency toward flexion at the elbow and wrist, with pronation of the forearm and fingers kept closed or fisted. Affected hips are adducted and are “scissored” in extreme cases. There is partial flexion at the knees and plantarflexion at the ankles. Torticollis and truncal hyperextension or twisting may also be present. After inspection, the clinician may perform passive range of motion, revealing increased tone in the affected limb. Typical of spasticity is “velocity dependence, meaning resistance increases with more rapid passive movement. In some cases, a spastic “catch” may be elicited in a limb with passive joint extension in which the increase in tone is momentarily reduced. Tone may also be increased in states of stress or excitement and decreased in sleep. In long-standing or severe cases, range of motion may be limited by secondary joint contractures, which typically evolve later in infancy or childhood. Strength may be intact, although this varies, and an element of weakness and motor fatigue is common. Reflex testing reveals hyperreflexia. This is the result of a hyperexcitable stretch reflex and in extreme forms presents as clonus. Extensor plantar responses (i.e., Babinski’s sign) may be present on the affected side. Children with spastic CP may experience difficulties with fine motor movements (e.g., sequential finger movements) or in isolated effortful movements. In mild cases, this may appear as “clumsiness” with easy fatigability. Observation of gait is helpful both in recognizing the pattern of involvement and in assessing functional impairment.

Figure 77-2 Characteristic pattern in spastic limbs.

Dyskinetic Cerebral Palsy

Dyskinetic CP comprises about 15% of CP. Involuntary movements interfering with voluntary motor function are characteristic. Dyskinetic CP may be further divided by primary movement type into choreoathetoid CP and dystonic CP (Figure 77-3). Choreoathetoid movements have a smooth, fluctuating dancelike quality (chorea) and a writhing or wriggling quality (athetosis) in the distal extremities. Dystonia is abnormal sustained movement or posturing in a repetitive, patterned fashion. Although dystonias are also quite common in spastic CP, dystonic CP refers to the case in which dystonia is the primary feature. Even in retrospect, dyskinetic CP may not be noticed until after age 2 or 3 years because infants without CP have some degree of choreoathetoid movement. The movement disorder in dyskinetic CP reflects injury to the basal ganglia. Clinical history should explore risk factors for such injury, including hyperbilirubinemia or hypoxic ischemic injury at term or postnatally. Children with dyskinetic CP are often described as having “fluctuating tone.” This reflects involuntary, often sustained muscle contraction that may be mistaken for intermittent spasticity. The physical examination should include observation of involuntary movements, recognizing that multiple movement types may be present. Sustained posture (e.g., extension of the arms) or distraction may elicit involuntary movements. Serial assessments of tone may be necessary to characterize whether spasticity is also present.