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Transient and Developmental Movement Disorders
Introduction
The presence of a movement disorder in a child usually raises concerns about an underlying serious, progressive, degenerative, or metabolic disease. However, many movement disorders are benign and related to normal stages of development. In fact, it may be difficult to justify the term “disorder” in describing many of these movements. The developing nervous system may produce a variety of motor patterns that would be pathological in older children and adults but in young children are simply a manifestation of CNS immaturity. Like many of the neonatal reflexes (e.g., grasping, rooting, placing, tonic neck reflexes), these motor patterns disappear as neuronal network connectivity and myelination matures. Examples include the minimal chorea of infants and young children (“chorea minima”), the mild action dystonia commonly seen in toddlers, and the overflow movements that are commonly seen in young children.
Other transient or developmental movement disorders may be manifestations of abnormal neural function, but do not correlate with serious underlying pathology. These are typically associated with complete resolution of the abnormal movements and ultimately normal development and neurological function. Most of these conditions occur during infancy or early childhood ( Table 6.1 ). It is important to recognize these transient developmental movement disorders, distinguish them from more serious disorders, and be able to provide reassurance when appropriate.
Table 6.1
Transient Developmental Movement Disorders of Infancy and Childhood
| Disorder | Age at Onset | Age at Resolution | Treatment |
|---|---|---|---|
| Benign neonatal Sleep myoclonus |
Less than 1 month | Six months | Reassurance |
| Benign myoclonus of early infancy | 3–9 months | Typically by 15 months | Reassurance |
| Jitteriness | 1st week of life | Typically before 6 months | Reassurance |
| Shuddering | Infancy, early childhood | Unknown | Reassurance |
| Paroxysmal tonic Upgaze (downgaze) of infancy |
Usually first year of life | Usually age 1–4 years | Levodopa may be effective |
| Spasmus nutans | 3–12 months | Within a few months, but subtle nystagmus may persist for years | Reassurance |
| Head nodding | Before age 3 years | May persist for years | Reassurance |
| Benign paroxysmal Torticollis |
First year of life | By 5 years | Reassurance Topiramate may be effective |
| Benign idiopathic Dystonia of infancy |
Before 5 months | By 1 year | Reassurance |
| Infantile masturbation | Before 3 years | Becomes more covert | Reassurance |
Benign Neonatal Sleep Myoclonus
Benign neonatal sleep myoclonus is characterized by repetitive myoclonic jerks occurring during sleep. The myoclonic jerks typically occur in the distal more than proximal muscles and are more prominent in the arms than the legs. In some cases, jerks of axial or facial muscles can be seen. The myoclonus can be focal, multifocal, unilateral, or bilateral. The movements can be rhythmic or nonrhythmic. Typically, the movements occur in clusters of jerks at 1–5 Hz over a period of several seconds. Benign neonatal sleep myoclonus begins during the first month of life, diminishes in the second month and is usually gone before 6 months of age, but has been reported to persist as long as 3 years. , Ictal and interictal EEG are typically normal, but the myoclonus may be followed by a somatosensory response visible on jerk-locked EEG. The movements are most likely to occur during quiet (non-REM) sleep. They can also be triggered by noise. Waking the baby causes the movements to cease. Episodes of myoclonus can be exacerbated by treatment with benzodiazepines. Familial cases have been reported. , One study suggested a subsequent association with migraine during childhood. Treatment is not required and neurological outcome is typically normal.
Benign Myoclonus of Early Infancy (Benign Infantile Spasms)
Benign myoclonus of early infancy (BMEI) was initially characterized as episodes of myoclonic spasms involving flexion of the trunk, neck, and extremities in a manner resembling the infantile spasms of West syndrome. , The myoclonic spasms typically occur in clusters. There is no change in consciousness during the spells. Unlike benign neonatal sleep myoclonus, the movements in BMEI only occur in the waking state. Because of their resemblance to infantile spasms, a video EEG including awake and sleeping states is warranted to rule-out infantile spasms. The cause of BMEI is unknown and most cases are idiopathic. A single case of BMEI in a child who also had a PRRT2 mutation has been reported, but it is not known whether this is a causal association.
In BMEI, the onset of these spells is usually between ages 3 and 9 months, but they may begin in the first month of life. The spells usually cease within 2 weeks–8 months of onset, but may persist for 1–2 years. Both ictal and interictal EEGs are normal, distinguishing this entity from infantile spasms. Treatment is not required. Development and neurological outcome are normal.
Although the original descriptions of BMEI emphasized the similarity to infantile spasms, a more recent review has advocated for inclusion of a variety of somewhat similar spells under the category of BMEI. These include (1) myoclonus, (2) spasms and brief tonic contractions, (3) shuddering, (4) atonia or negative myoclonus, or (5) more than one type of motor phenomenon. While it is true that normal infants may manifest a variety of benign nonepileptic paroxysmal movements, as described through this chapter, it remains useful to approach these entities systematically based initially on the phenomenology of the spells.
Jitteriness
Jitteriness is a movement disorder that is commonly observed in the neonatal period. Jitteriness manifests as generalized, symmetric, rhythmic oscillatory movements that resemble tremor or clonus. Up to 50% of term infants exhibit jitteriness during the first few days of life, especially when stimulated or crying. Jitteriness usually disappears shortly after birth, but can persist for months or recur after being gone for several weeks. , Persistent jitteriness has been associated with hypoxic-ischemic injury, hypocalcemia, hypoglycemia, adrenal insufficiency, vitamin D deficiency, inborn errors of metabolism, and drug withdrawal. Jitteriness is highly stimulus sensitive. It can be precipitated by startle and suppressed by gentle passive flexion of the limb. Unlike seizures, there are no associated abnormal eye movements or autonomic changes. Idiopathic jitteriness is usually associated with normal development and neurologic outcome. The outcome of infants with symptomatic jitteriness depends on the underlying cause.
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