Central paralysis and paresis

Classification of motor disorders

Depending on which specific structures of the nervous system are damaged, there are four main types of paralysis and paresis:

• Central (also known as pyramidal or spastic);
• Peripheral;
• Extrapyramidal;
• Myasthenic (associated with impaired neuromuscular transmission).

Clinical manifestations of central paralysis

The pathogenetic basis of spastic paresis is damage to the pyramidal system. Due to the weakening of inhibitory descending influences from the brain, the segmental apparatus of the spinal cord becomes disinhibited. This forms a classic symptom complex:

1. Hyperreflexia. Manifested by an increase in segmental tendon and periosteal reflexes. At the same time, the amplitude of the reflex response increases significantly, and reflexogenic zones expand.
2. Muscle hypertonia of the spastic type. Tone in central paralysis increases unevenly. A typical distribution is formed: in the arm, spasticity predominates in the adductor muscles of the shoulder and flexors of the forearm; in the leg, the extensors of the thigh and leg, the adductors of the thigh, and the flexors of the foot are tense. Over time, such persistent movement restriction leads to the fixation of the limb in an unusual position — neurogenic contractures develop.
3. Pathological reflexes. Subdivided into flexor and extensor ones (e.g., Babinski, Rossolimo, Bechterew reflexes). Extensor reflexes serve as one of the earliest and most constant signs of pyramidal tract damage.
4. Clonus. Represents an extreme, high degree of severity of tendon-muscle reflexes. Clinically, it looks like a series of rapid rhythmic muscle contractions (spontaneous or in response to stimulation). Most commonly observed as foot, patellar, hand, or jaw clonus.
5. Syncinesias. These are involuntary associated muscle contractions. They occur in the paralyzed limb when the patient performs a conscious movement with the healthy limb or another part of the body. They are mediated by the participation of the spinal cord, cerebellum, and pyramidal system.

Extrapyramidal disorders (rigidity)

When the extrapyramidal system is damaged (which is typical, for example, for parkinsonism), a different type of tone change develops — rigid paresis. Its pathogenetic mechanism consists of a simultaneous increase in tone in both flexors and extensors.

Clinically, this is manifested by the "lead-pipe rigidity" phenomenon: the patient's torso or limb is able to maintain the posture imparted to it from the outside for a long time.

Peripheral (flaccid) paralysis

The pathogenetic basis of peripheral paralysis is primary (hereditary, congenital) or acquired lesions of the peripheral motor neurons themselves (cells of the anterior horns of the spinal cord, cranial nerve nuclei).

Acquired injuries develop under the influence of various factors:

• Inflammatory processes (poliomyelitis, encephalitis);
• Intoxication by neurotropic poisons (diphtheria or botulinum toxins);
• Mechanical trauma;
• Degenerative changes (for example, in amyotrophic lateral sclerosis — ALS);
• Neuromuscular transmission disorders (in myasthenia gravis, botulism, the action of aminoglycoside antibiotics and other toxins).

In typical cases, a flaccid paralysis symptom complex forms:

1. Hypotonia. Muscles become flabby and flaccid due to the cessation of nerve impulses and a significant decrease in axonal nutrient supply.
2. Areflexia or hyporeflexia. Segmental (cutaneous, tendon, periosteal) reflexes are reduced or completely lost due to denervation and rupture of the reflex arc.
3. Atrophy and hypotrophy. Occurs in the area of damage as a consequence of prolonged disuse and loss of neurotrophic influences on the muscles.
4. Degeneration of muscle fibers. Due to trophic deficiency, muscle tissue is gradually replaced by adipose and connective tissue.
5. Decreased muscle excitability. Develops against the background of various forms of muscular dystrophy and is designated by the term muscle "degeneration" phenomenon.

Briefly: answers to topical questions

Class and exam questions

What else to study on this topic

• Pathological reflexes (Babinski, Rossolimo, Bechterew): elicitation technique and evaluation
• Mechanism of formation and prevention of neurogenic contractures
• Amyotrophic lateral sclerosis (ALS) as a cause of motor neuron degeneration
• Effect of aminoglycoside antibiotics on neuromuscular transmission
• The phenomenon of muscle "degeneration" in flaccid paralysis

Other topics in "Chapter 28. Standard forms of pathology of the nervous system"

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