Epidemiology of Hypertonia in Children

Incidence and Prevalence

Cerebral palsy

• 1.5 to 4 per 1000 live births per year: The prevalence of CP in modern western societies varies between 1.5 and 4 per 1,000 children in any defined age group including newborns (2-6).
• 41% have mobility disability: Nearly half of children with CP have an associated problem with walking, running, or playing (7).

Familial spastic paraparesis

• 1.3 to 9.6 per 100,000: Studies have cited a prevalence of familial spastic paraparesis that varies between 1.3 and 9.6 per 100, 000 (8).

Age Distribution

Cerebral palsy

• Static perinatal injury: Neurological impairments in the preterm infant during the first year of life may resolve over time. Because of the transience of neurological findings in the population, the variability in patient performance from examination to examination, the inconsistency in diagnostic testing, and the absolute dependence of the diagnosis on clinical examination findings, CP is generally diagnosed after serial examinations. As described earlier, the most common cause of spasticity is CP. Spasticity may be evident by the first year of life.
• Manifestations and severity change with age: Half the children diagnosed with spastic diplegia at 1 year of age had outgrown the diagnosis by age 6. This may be related to myelination occurring during that time interval, especially between the ages of 4 to 6 years. For SDR, surgery should be avoided for children younger than 2 years because of the frequency of resolution of motor symptoms in this group (9, 10).

Familial spastic paraparesis

• Any age: Symptoms can begin at any age. When they are evident early in life, they tend to be nonprogressive, resembling CP, while symptoms of spasticity that develop later tend to be slowly progressive (8).

Sex Predilection

Cerebral palsy

• Possible male preponderance: While there is disagreement on the subject of sex-based differences in spastic CP (11), very preterm males may be more likely to be affected by the condition (12). Recent evidence also suggests a sex-specific improvement in psychomotor outcomes for females with spastic hemiplegia (13).

Familial spastic paraparesis

• X-linked form: One form of familial spastic paraparesis is X-linked.

Geographic Distribution

Cerebral palsy

• None apparent

Familial spastic paraparesis

• Familial pockets: The hereditable nature of this condition coupled with normal life span leads to pockets of occurrence.

Risk Factors

Prematurity

• 40–50% of children with CP are born prematurely: The exact causes are unknown: the immature brain exhibits an increased vulnerability to injury either from events affecting the mother during the pregnancy or from events affecting the infant during or after birth.

Term infants

• Injuries to CNS during birth: Even at term injuries can occur to an infant’s nervous system that will result in a fixed deficit and an associated disability. Causative factors for such injuries include anoxic episodes, infections, and metabolic derangements.

Early childhood

• CNS injuries during first several years of life: Many include nonprogressive injuries to the CNS during the first 2 or so years after birth with other causes of CP. Although the characteristics of the symptoms will vary according to the degree of development of the nervous system, the resulting disabilities are similar.

Genetics

• Reported in CP: Up to 2% of cases of CP have been reported to be genetic in origin (14, 15). The authors cite a lack of contributing factors and multiple family members with the condition as evidence for their reported cases being inherited. Consanguinous marriages have been considered a risk factor, as reported from Pakistan where four children with spastic CP and mental retardation have been identified (16, 17). When there is suspicion of an inherited spastic paraparesis, familial spastic paraparesis must be considered.
• Autosomal dominant, autosomal recessive, and X-linked forms of familial spastic paraparesis