Motor syndromes

Central paresis and its topography

The clinical presentation of central paresis varies depending on the level of damage to the corticospinal (pyramidal) tract.

• Cerebral cortex: A lesion in the middle sections of the precentral gyrus results in a central monoparesis of the contralateral arm. Involvement of the upper and medial sections leads to monoparesis of the leg. If the medial sections are affected bilaterally, lower paraparesis develops.
• Cerebral peduncles: Spastic hemiparesis occurs on the opposite side. With concomitant involvement of the oculomotor nerve on the side of the lesion, Weber's syndrome is formed.
• Pons: The pyramidal pathway fibers are dispersed here, so hemiparesis is rarely complete. The facial and hypoglossal nerves usually remain intact (their fibers deviate posteriorly), but the trigeminal or abducens nerves on the affected side may be involved.
• Medulla oblongata (pyramids): An isolated lesion results in a flaccid contralateral hemiparesis. Weakness rarely reaches complete plegia, as other descending pathways remain intact.
• Spinal cord: A unilateral lesion of the lateral funiculus in the cervical region causes ipsilateral spastic hemiplegia. A bilateral lesion at the upper cervical level leads to tetraparesis, and at the thoracic level, to lower paraparesis.

Peripheral paresis

Occur when the structures of the peripheral motor neuron are damaged and are always flaccid in nature.

• Anterior horn syndrome: Damage to the anterior horn motor neurons, roots, or spinal nerves causes flaccid paresis in the corresponding myotomes. A specific marker is the presence of fasciculations.
• Plexopathies: Damage to the cervical and brachial plexuses leads to weakness in the muscles of the shoulder girdle and arm. Damage to the lumbosacral plexus leads to paresis of the pelvic girdle and leg.
• Neural amyotrophy: Isolated damage to peripheral nerves. In addition to flaccid paresis, pain, sensory disorders, and autonomic disturbances are often observed in the innervation zone.

Combined spinal cord lesions

Certain diseases selectively affect multiple spinal cord tracts simultaneously.

1. Amyotrophic lateral sclerosis: Bilateral lesion of the anterior horns and pyramidal tracts. It debuts with heaviness and weakness in the legs. A specific topography is characteristic: flaccid paresis in the distal parts of the arms (hands, forearms) is combined with spastic paresis of the trunk and legs. Tendon reflexes are brisk.
2. Progressive spastic spinal paralysis: Isolated bilateral degeneration of the corticospinal tracts with intact anterior horns. Manifests as diffuse spastic tetraparesis without zones of flaccid paresis.
3. Friedreich's ataxia: Debuts before the age of 20 with the loss of dorsal root ganglion cells. The posterior columns (loss of joint position sense, sensory ataxia), spinocerebellar tracts (cerebellar ataxia), and pyramidal tracts (spastic paresis) are affected. Pain and temperature sensitivity remain preserved. Scoliosis and a hollow foot (pes cavus) are detected in 50% of patients.

Muscle tone dynamics in an acute lesion

In an acute lesion of the central motor neuron, muscle tone changes in stages:

• Shock phase: In the first hours or days on the side opposite to the lesion, muscle tone is reduced. Clinically, this appears as flaccid paresis.
• Transformation: Hours or days later, the paresis acquires a typical spastic character. Pathogenetically, this is due to the concurrent involvement of the extrapyramidal system's motor fibers in the process.

Class and exam questions

What else to study on this topic

• Differential diagnosis of spinocerebellar ataxias
• Hereditary motor and sensory neuropathy type II (axonal form)
• Topography of lesions in the cortex and subcortical white matter of the frontal lobe
• Internal capsule lesion syndromes

Other topics in the section "DeMyer's The Neurologic Examination" / "Duus' Topical Diagnosis in Neurology"

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