Changes in the reflex sphere in motor pathway pathology
The state of reflexes directly reflects the level of the nervous system lesion. In amyotrophic lateral sclerosis, which combines damage to the anterior horns and lateral funiculi, exaggeration of tendon reflexes (hyperreflexia) is observed alongside progressive spastic lower extremity paresis.
In turn, in Friedreich ataxia, one of the key diagnostic criteria (according to Harding) is the complete absence of tendon reflexes in the lower extremities, caused by degeneration of spinal ganglia and posterior funiculi.
Spinal automatisms and protective reflexes
After the period of acute spinal shock resolves, the isolated segment of the spinal cord begins to function autonomously. This leads to the appearance of pathological reflex responses:
- Protective flexion reflex (triple shortening reflex): involuntary flexion of the lower extremity at the hip, knee, and ankle joints in response to a stimulus.
- In complete transverse lesions, the leg remains flexed for a prolonged period after stimulation due to hypertonia.
- In incomplete lesions, the limb first flexes and then returns to its initial position.
Reflex disorders in epiconus and medullary cone lesions
Topical diagnosis of lower spinal cord segment lesions is based on assessing the preservation of specific reflex arcs:
- Epiconus (L4–S2): The Achilles reflex is lost, while the knee reflex remains preserved. Reflex bladder emptying is impaired.
- Medullary cone (below S3): The anal reflex is lost, and detrusor areflexia is noted. An important distinguishing feature is the preservation of the Achilles reflex, as its arc closes higher (L5–S2).
Briefly: answers to topical questions
What are the causes and level of lesion in Brown-Séquard syndrome?
Brown-Séquard syndrome occurs when half of the transverse area of the spinal cord (hemisection) is damaged.
Main causes:
- spinal cord injury;
- intervertebral disc herniation, predominantly in the cervical region;
- spinal cord compression by a tumor (lateral compression).
Class and exam questions
What happens to tendon reflexes in central motor neuron syndrome?
Tendon reflexes become exaggerated, hyperreflexia develops, and pathological signs appear, such as the Babinski sign.
Which reflex helps differentiate acute transverse spinal cord injury from polyradiculitis?
Bulbocavernous reflex. It is preserved in acute transverse spinal cord injury and is usually absent in polyradiculitis.
Is the Achilles reflex preserved in medullary cone lesions?
Yes, it is preserved because the reflex arc of the Achilles reflex closes at the L5–S2 level, whereas the cone is located below S3.
What else to study on this topic
- Combined anterior horn and pyramidal tract lesion syndrome
- Brown-Séquard syndrome and its manifestations
- Harding's diagnostic criteria for Friedreich ataxia
- Complete transverse spinal cord injury syndrome
- Topical diagnosis of epiconus and medullary cone lesions
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