OVERVIEW OF MOVEMENT DISORDERS
Movements disorders are neurologic syndromes that involve impaired performance of voluntary movements, dysfunction of posture, the presence of abnormal involuntary movements, or the performance of normal-appearing movements at inappropriate or unintended times.1,2 These movement abnormalities are not due to weakness or spasticity. Movement disorders are traditionally divided into hyperkinetic disorders and hypokinetic disorders. Hyperkinetic movement disorders are characterized by an excess of movement, whereas hypokinetic movement disorders are characterized by a paucity of movement. In childhood, hyperkinetic movement disorders are far more common than hypokinetic movement disorders. Hyperkinetic movement disorders include tics, stereotypies, chorea, athetosis, ballism, dystonia, myoclonus, and tremor. The primary hypokinetic movement disorder is parkinsonism, which is characterized by bradykinesia, tremor, rigidity, and postural instability. Parkinson's disease, which is the most common hypokinetic movement disorder in adults, is exceedingly rare in children.
Movement disorders arise from abnormalities in the basal ganglia circuits. The basal ganglia are subcortical structures including the striatum (caudate, putamen, nucleus accumbens), the subthalamic nucleus, the globus pallidus (internal segment, external segment, ventral pallidum), and the substantia nigra (pars compacta, pars reticulata). Input to the basal ganglia come from the cerebral cortex and the thalamus. Most of the output of the basal ganglia is from the globus pallidus internal segment, ventral pallidum, and substantia nigra pars reticulata. The output is predominantly inhibitory to the brainstem and to the thalamic nuclei, which project back to the cerebral cortex. These complex circuits function to facilitate wanted patterns of movement and inhibit unwanted patterns of movement. In addition to motor control, the basal ganglia likely have a role in cognitive and emotional control.2
Of importance to the clinician, the basal ganglia and the cerebellum function together in their control of the corticospinal and extrapyramidal systems. Corticospinal syndromes are characterized by the loss of volitional movement with spasticity. In contrast, extrapyramidal syndromes are characterized by the presence of involuntary movements (Table 62–1).
Table 62–1Clinical Differences between Corticospinal and Extrapyramidal Syndromes ||Download (.pdf) Table 62–1 Clinical Differences between Corticospinal and Extrapyramidal Syndromes
| ||Corticospinal ||Extrapyramidal |
|Character of the alteration of muscle tone ||Clasp-knife effect (spasticity) ||Plastic, equal throughout passive movement (rigidity), or intermittent (cogwheel rigidity) |
|Distribution of hypertonus ||Flexors of arms, extensors of legs ||Generalized but predominates in flexors of limbs and of trunk |
|Involuntary movements ||Absent ||Presence of tremor, chorea, athetosis, dystonia |
|Tendon reflexes ||Increased ||Normal or slightly increased |
|Babinski's sign ||Present ||Absent |
|Paralysis of voluntary movement ||Present ||Absent or slight |
CLASSIFICATION OF MOVEMENT DISORDERS
Multiple schemes are used to classify movement disorders. They can be classified based on clinical features (e.g., age of onset, body distribution, phenomenology, response to treatment), etiologic criteria (primary vs. secondary), anatomic localization, neuropathologic findings, or genetic and molecular criteria.3–7 Often, multiple classifications systems are used simultaneously. For ...