Definition of Parkinsonian syndrome
Parkinsonism syndrome (hypertonic-hypokinetic, or akinetic-rigid syndrome) is one of the syndromes involving basal ganglia lesions. Its key manifestations are hypokinesia (reduced amplitude and number of movements) and muscle rigidity (plastic-type increased muscle tone). Mnemonic connection to the anatomical substrate is easily remembered via the letter "P": parkinsonism — pallidal lesion.
Anatomical and Physiological Foundations
The extrapyramidal system is responsible for regulating involuntary movements and forming motor programs. Any voluntary action (such as picking up a pen) consists of the sequential activation of agonist and antagonist muscles, and this program is implemented via subcortical structures.
The main level of regulation is the striopallidal system. Impulses from the frontal motor cortical areas (primary motor, premotor, and supplementary motor areas) arrive primarily at the striatum — the main afferent input of the extrapyramidal system. Then, via the globus pallidus (internal and external segments), subthalamic nucleus, substantia nigra, and thalamus, cortical activity is modulated.
Direct Dopaminergic Pathway and Pathogenesis
The source of dopamine in the central nervous system is the pars compacta of the substantia nigra. Dopamine travels via the nigrostriatal pathway to the striatum. In the direct pathway, dopamine binds to D1 receptors of the striatum, enhancing its inhibitory effect on the internal segment of the globus pallidus. The latter, in turn, ceases to inhibit the thalamus, and the thalamus activates the primary motor cortex, from which impulses travel via the pyramidal pathway to motor neurons — resulting in movement.
In parkinsonism, degeneration of neurons in the pars compacta of the substantia nigra and loss of the direct dopaminergic pathway occur. The inhibitory influence of the striatum on the globus pallidus disappears, the globus pallidus excessively inhibits the thalamus, motor cortex activation decreases — leading to hypokinesia and rigidity.
Dopamine deficiency affects not only motor structures but also the limbic system (emotions, motivation), frontal cortex (thinking), and hypothalamus (autonomic regulation), which explains non-motor symptoms.
Motor Symptoms
- Plastic rigidity — a uniform increase in tone in both flexors and extensors, persisting throughout passive movement (unlike spasticity in pyramidal paralysis).
- Hypokinesia — a decrease in motor activity without paralysis orparesis. Includes: oligokinesia (reduction in the number of movements), bradykinesia (slowness of movement), freezing episodes, and the "air pillow" sign.
- Hypomimia — impoverishment of facial expression, mask-like face.
- Bradylalia — slowed, quiet speech.
- Acheiromegaly — absence of associated arm movements during walking.
- Postural disturbances: pro-, retro-, and lateropulsion — the patient is unable to correct posture when pushed and continues moving by inertia.
- Paradoxical kinesia — a short-term regression of symptoms against the background of intense emotions due to the release of endogenous dopamine.
Resting Tremor
Resting tremor is characteristic, appearing at rest and diminishing during voluntary movements. It is predominantly localized in the distal parts of the upper extremities and has a stereotyped pattern resembling "pill-rolling" or "counting coins". This sign is one of the most specific for parkinsonism.
Non-Motor Manifestations
- Autonomic disorders: tendency to constipation, hypersalivation, hyperhidrosis, arterial hypotension, bradycardia.
- Cognitive changes: bradyphrenia (slowness of thought), akairia — viscosity and sluggishness of thought, tendency to get stuck on a single idea.
- Affective disorders: depression, decreased motivation, emotional poverty, associated with dopamine deficiency in the limbic system.
Key points
- Parkinsonism is an akinetic-rigid syndrome of basal ganglia lesions.
- The pathogenesis is based on the degeneration of neurons in the pars compacta of the substantia nigra and the loss of the direct nigrostriatal dopaminergic pathway.
- Dopamine deficiency leads to excessive inhibition of the thalamus and decreased activation of the motor cortex.
- Rigidity has a plastic character — a uniform increase in tone in flexors and extensors.
- Hypokinesia includes oligokinesia, bradykinesia, hypomimia, bradylalia, acheirokinesia, and postural disturbances.
- Resting tremor of the "pill-rolling" type is a pathognomonic motor sign.
- Paradoxical kinesia demonstrates the preservation of motor programs despite dopamine deficiency.
- Non-motor symptoms (bradyphrenia, depression, autonomic dysfunction) are caused by dopamine deficiency in the limbic system, frontal cortex, and hypothalamus.