Extrapyramidal syndromes

Which brain structures form the extrapyramidal system?

The extrapyramidal system is formed by subcortical nuclei (basal ganglia) deep within the cerebral hemispheres and brainstem nuclei. These include:

• Caudate nucleus (nucleus caudatus)
• Putamen (putamen)
• Globus pallidus (globus pallidus)
• Subthalamic nucleus
• Substantia nigra (substantia nigra)
• Red nucleus (nucleus ruber)
• Reticular formation (formatio reticularis)

The caudate nucleus, putamen, and globus pallidus combine into a structure called the striatum (striatum).

What symptoms are included in the classical triad of akinetic-rigid syndrome?

The classical clinical triad of akinetic-rigid syndrome (parkinsonism) includes akinesia, rigidity, and resting tremor.

• Akinesia — difficulty initiating or completing a movement.
• Rigidity — increased muscle tone of the "lead-pipe" or "wax-like" type (plastic change in tone).
• Resting tremor — shaking of the head and limbs that disappears during movement.

How does extrapyramidal muscle rigidity differ from pyramidal spasticity?

Extrapyramidal muscle rigidity differs from pyramidal spasticity by the preservation of muscle strength and the absence of pathological reflexes. Rigidity is characterized by a uniform increase in tone in both flexors and extensors (plastic tone).

Damage to which brain structure causes hemiballism?

Hemiballism occurs due to damage to the subthalamic nucleus. This hyperkinesia manifests as large-amplitude, sweeping, flinging movements in the limbs (primarily in the proximal joints). The disorder is unilateral and develops on the side of the body opposite (contralateral) to the lesion.

What types of hyperkinesia are classified as extrapyramidal disorders?

Extrapyramidal disorders include the following types of hyperkinesia:

• Tremor — involuntary rhythmic oscillations of a body part.
• Tics — rapid, stereotypical, repetitive contractions of individual muscle groups.
• Dystonia — involuntary, slow, sustained muscle contractions resulting in abnormal postures.
• Chorea — irregular, abrupt movements in the muscles of the limbs, trunk, and face.
• Athetosis — slow, "worm-like" movements, mostly in the distal extremities.
• Ballism — large-amplitude, sweeping, flinging movements.
• Myoclonus — sudden, brief, shock-like jerks of individual limb segments.

What neurotransmitter deficiency underlies the pathogenesis of Parkinson's disease?

The pathogenesis of Parkinson's disease is based on dopamine deficiency. It results from the loss of melanin-containing dopaminergic neurons in the pars compacta of the substantia nigra (substantia nigra pars compacta). This leads to a decrease in dopamine production and a reduction of its content in nigrostriatal synapses, which causes decreased activation of the motor areas of the frontal lobe cortex and the development of akinetic-rigid syndrome.

What is the "cogwheel" phenomenon when examining muscle tone?

The "cogwheel" phenomenon consists of intermittent, ratchet-like muscle resistance during passive movement. This symptom is detected during an objective examination of muscle tone in patients with extrapyramidal muscle rigidity. The mechanism of this phenomenon is due to the superposition of tremor on the plastic increase in muscle tone (rigidity).

What clinical manifestations are characteristic of choreic hyperkinesia?

Choreic hyperkinesia is characterized by irregular, abrupt movements in the muscles of the limbs, trunk, and face that constantly replace each other in an unpredictable sequence. Clinical manifestations include:

• Involuntary grimaces and chaotic movements.
• Noisy breathing.
• Unsteadiness when walking.
• Pronounced muscle hypotonia in the intervals between movements.

The amplitude of hyperkinesia varies from minimal twitches to generalized sweeping movements ("choreic storm").

Which pathways provide connections within the striopallidal system?

Connections within the striopallidal system (basal ganglia) are provided by the direct and indirect pathways.

• Direct pathway — GABAergic fibers run from the striatum to the internal segment of the globus pallidus.
• Indirect pathway — involves signal transmission from the striatum to the external segment of the globus pallidus, after which GABAergic fibers project to the subthalamic nucleus, which in turn sends glutamatergic fibers to the internal segment of the globus pallidus.

Both pathways ultimately project from the internal segment of the globus pallidus to the thalamus.

What general groups of neurological disorders accompany extrapyramidal syndromes?

Extrapyramidal syndromes are accompanied by three general groups of neurological disorders. These include:

• Slowness of movement (hypokinesia or akinesia).
• Involuntary movements (hyperkinesia).
• Disorders of muscle tone — its increase (rigidity) or decrease (muscle hypotonia).

Depending on the predominance of these disorders, two main syndromes are distinguished: akinetic-rigid and hypotonic-hyperkinetic.