What is cerebral palsy?

What is Cerebral Palsy

Cerebral palsy is 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. 1

Epidemiology and Prevalence

• Cerebral palsy is the most common physical disability in childhood, with a prevalence of 2 to 3 cases per 1000 live births in high-income countries 1, 2
• The prevalence is declining in Australia and Europe but appears higher in low to middle-income countries due to greater infectious disease burden and differences in prenatal and perinatal care 2

Core Characteristics

The disorder is characterized by permanent but non-progressive brain injury that manifests as motor impairments noted in the first years of life 1. The key distinguishing feature is that the brain disturbance itself does not progress, though clinical manifestations may evolve during early childhood 1.

Motor Types and Distribution

The motor impairments fall into four main categories:

• Spasticity (85%-91% of cases) - the most common form, characterized by increased muscle tone and velocity-dependent resistance to passive movement 1, 2
• Dyskinesia (4%-7%) - includes dystonia and athetosis 1, 2
• Ataxia (4%-6%) - affects coordination and balance 1, 2
• Hypotonia (2%) - decreased muscle tone, though not classified in all countries 1

Topographic Classification

Spasticity is further categorized by body distribution:

• Unilateral (hemiplegia) - affects one side of the body (38% of cases) 1, 2
• Bilateral diplegia - lower limbs affected more than upper limbs (37% of cases) 1, 2
• Quadriplegia - all four limbs and trunk affected (24% of cases) 1, 2

Etiology and Risk Factors

The underlying cause of cerebral palsy is uncertain in most cases, though multiple risk factors have been identified 1. Importantly, birth asphyxia accounts for less than 10% of cases, contrary to historical assumptions 1.

Established Risk Factors

• Genetic factors contribute to 14% of cases, with recent meta-analysis showing 31.1% diagnostic yield from exome sequencing 1, 2
• Maternal conditions including thyroid disease, preeclampsia, and infections 2
• Pregnancy complications such as intrauterine growth restriction and multiple gestation 2
• Prematurity and low birth weight - children born under 1500g have 70 times higher risk compared to those over 2500g 3
• Preconception risks including history of stillbirths, miscarriages, low socioeconomic status, and assisted reproduction 2
• Perinatal asphyxia (55% in some series) and infections, trauma, stroke, or hypoxic events in early infancy 2, 4

Common Comorbidities

Cerebral palsy rarely occurs in isolation - the majority of affected individuals have multiple associated impairments that significantly impact quality of life:

• Chronic pain (75%) 1, 2, 5
• Intellectual disability (27%-49%) 1, 5
• Epilepsy (35%-38%) 1, 2
• Speech disorders (33%-82%) 1
• Musculoskeletal problems including hip displacement (28%) 1, 2, 5
• Behavioral disorders (26%) 1, 2
• Sleep disorders (23%) 1, 2
• Visual impairment (11%) 1, 2
• Hearing impairment (4%) 1, 2
• Autism spectrum disorder (3%-9%) 1

Neuroimaging Patterns

Brain MRI reveals characteristic patterns that correlate with cerebral palsy etiology:

• White matter injury (56%) - including cystic periventricular leukomalacia or periventricular hemorrhagic infarctions 2
• Cortical and deep gray matter lesions (18%) - basal ganglia or thalamus lesions, watershed injury, multicystic encephalomalacia, or stroke 2
• Brain maldevelopments (9%) - lissencephaly, pachygyria, cortical dysplasia, polymicrogyria, or schizencephaly 2
• Anoxic-ischemic sequelae are commonly identified on imaging 4

Prognosis and Functional Outcomes

In high-income countries with appropriate management, functional outcomes are better than historically expected:

• 2 in 3 individuals will walk 1, 2
• 3 in 4 will talk 1, 2
• 1 in 2 will have normal intelligence 1, 2

Timing of Diagnosis

Diagnosis can now be made before 6 months' corrected age, much earlier than the historical standard of 12-24 months 1. The most predictive early diagnostic tools include:

• Before 5 months corrected age: Prechtl Qualitative Assessment of General Movements (98% sensitivity), term-age MRI (86%-89% sensitivity), and Hammersmith Infant Neurological Examination (90% sensitivity) 1, 2
• After 5 months corrected age: MRI (86%-89% sensitivity), Hammersmith Infant Neurological Examination (90% sensitivity), and Developmental Assessment of Young Children (83% C index) 1

Critical Management Principle

Early diagnosis and immediate referral to diagnostic-specific intervention is essential to optimize infant motor and cognitive plasticity, prevent secondary complications, and enhance caregiver well-being 1, 2. Delaying diagnosis can be harmful to parent and caregiver well-being, potentially leading to depression and lasting anger 2.