Describe the motor manifestations of cerebral palsy.

Motor Activity Description in Cerebral Palsy

Cerebral palsy manifests as permanent disorders of movement and posture development, with motor dysfunction being the essential diagnostic criterion that must be present in all cases. 1

Motor Type Classification

The motor manifestations are classified into four distinct types that may emerge and evolve during the first 2 years of life 1:

Spastic Cerebral Palsy (85-91% of cases)

• Characterized by brisk reflexes indicating upper motor neuron dysfunction, which is the hallmark of this most common motor type 2
• Presents with increased muscle tone and velocity-dependent resistance to passive movement 1
• Classified topographically as:
  • Unilateral (hemiplegia): 38% of cases, affecting one side of the body 1
  • Bilateral diplegia: 37% of cases, with lower limbs affected more than upper limbs 1
  • Quadriplegia: 24% of cases, involving all four limbs and trunk 1
• Truncal hypotonia combined with limb spasticity is well-documented, where different body regions show varying tone abnormalities 2

Dyskinetic Cerebral Palsy (4-7% of cases)

• Includes dystonia and athetosis 1
• Results from injury to basal ganglia or thalamus 3
• Usually affects all four limbs 1
• Characterized by involuntary, uncontrolled movements that interfere with voluntary motor control 4

Ataxic Cerebral Palsy (4-6% of cases)

• Presents with impaired coordination and balance 1
• Typically affects all four limbs 1
• Characterized by tremor and difficulty with precise movements 4

Hypotonic Cerebral Palsy (2% of cases)

• Presents with decreased muscle tone 1
• Not classified in all countries 1
• Important caveat: The absence of spasticity and normal tone cannot rule out cerebral palsy, as motor types may emerge and change during the first 2 years 5

Observable Motor Dysfunction Patterns

Essential Motor Abnormalities (Required for Diagnosis)

Motor dysfunction manifests as 1:

• Reduced quality of movement (e.g., absent fidgety general movements)
• Neurologically abnormal movements (e.g., early observable hand asymmetry)
• Motor activities substantially below chronological age expectations (e.g., head lag, not sitting, inability to grasp, or not reaching for toys when developmentally appropriate)

Age-Specific Motor Manifestations

• Before 5 months corrected age: Abnormal general movements and suboptimal Hammersmith Infant Neurological Examination scores are most predictive 5
• After 5 months corrected age: Developmental delays become more apparent, with inability to sit by 9 months being a red flag 2

Functional Motor Impairments

Selective Motor Control Deficits

• Loss of selective motor control interferes with gross motor function more than spasticity or range of motion deficits 6
• Children demonstrate inability to isolate movement of individual joints 6
• Wide variability exists in the relationship between spasticity, range of motion, and selective motor control 6

Range of Motion Limitations

• Spasticity and ROM deficits must be measured across multiple muscles and joints due to variable distribution 6
• Secondary musculoskeletal complications develop, including hip displacement (28% prevalence) 1

Gross Motor Function

• In high-income countries, 2 in 3 individuals with cerebral palsy will walk, though severity varies widely 1
• Gross Motor Function Classification System (GMFCS) levels range from I (walks without limitations) to V (transported in manual wheelchair) 2
• Motor severity is difficult to accurately predict in infants younger than 2 years because almost half have their GMFCS reclassified 5

Pathophysiological Mechanisms

Neurological Basis

• Abnormal segmental and supraspinal control of motor neuron output exists in spastic cerebral palsy 3
• Decreased presynaptic inhibition of Ia afferents and decreased nonreciprocal Ib inhibition contribute to motor dysfunction 3
• Early cerebral injury results in reorganization of corticospinal inputs to motor neuron pools 3

Progressive Secondary Changes

• The central nervous system damage causes increased collagen deposition around muscles, accumulating throughout life despite the brain lesion being non-progressive 7
• This explains why clinical features evolve with age and may lead to deterioration of motor function over time 7

Clinical Pitfalls to Avoid

• In milder presentations, especially unilateral cerebral palsy, infants may score within normal range on standardized motor assessments while still displaying abnormal movements 1
• For example, an infant with hemiplegia might obtain normal fine-motor scores but complete assessments one-handed 1
• Assessments must be performed by professionals skilled at determining atypical movement from variation in typical movement 1
• Any acute neurological deterioration requires urgent evaluation, as cerebral palsy is non-progressive by definition 2