Hyperkinetic movement disorders

Clinic

• HMDs or dyskinesias, refer to a group of excessive, abnormal and involuntary movements.
• Contrary to its name, they are not a group of diseases, but a group of entities that all have one thing in common, which is excessive, abnormal and involuntary movements.
• Here is the list of theses entities:
  • Tremor
  • Dystonia
  • Myoclonus
  • Tic
  • Chorea
  • Athetosis
  • Stereotypies

Pathogenesis

• Improper modulation of the basal ganglia by the subthalamic nucleus.
• In many cases, the excitatory output of the subthalamic nucleus is reduced, leading to a reduced inhibitory outflow of the basal ganglia.
• Without the normal restraining influence of the basal ganglia, upper motor neurons of the circuit tend to become more readily activated by inappropriate signals, resulting in the characteristic abnormal movements.

Since the basal ganglia often have many connections with the frontal lobe of the brain, hyperkinesia can be associated with neurobehavioral or neuropsychiatric disorders such as mood changes, psychosis, anxiety, disinhibition, cognitive impairments, and inappropriate behavior.

In children, primary dystonia is usually inherited genetically. Secondary dystonia, however, is most commonly caused by dyskinetic cerebral palsy, due to hypoxic or ischemic injury to the basal ganglia, brainstem, cerebellum, and thalamus during the prenatal or infantile stages of development. Chorea and ballism can be caused by damage to the subthalamic nucleus. Chorea can be secondary to hyperthyroidism. Athetosis can be secondary to sensory loss in the distal limbs; this is called pseudoathetosis in adults but is not yet proven in children.