Muscle tone disorders and pathological postures
Assessment of muscle tone is performed by carrying out passive movements in all joints of the patient's limbs. The physician analyzes the resulting resistance. When cortico-muscular pathways are damaged, spastic hypertonia develops, characterized by the "clasp-knife" phenomenon. When attempting to stretch the muscle (for example, arm flexors or leg extensors), the examiner initially feels marked resistance, which then suddenly gives way.
Tone in spastic hemiparesis is distributed unevenly. In the upper extremities, it is maximally increased in the flexors and shoulder adductors, while in the lower extremities, it is increased in the extensors and thigh adductors.
This pattern forms the classic Wernicke-Mann posture. In a patient with central hemiparesis, the affected arm is adducted to the trunk, flexed at the elbow joint, and pronated. Meanwhile, the leg is extended at the knee joint, and the foot is in plantar flexion. In muscular hypotonia or atonia, muscle tension in response to passive stretching is completely absent.
Assessment of muscle strength and detection of mild paresis
The severity of paresis is graded on a scale:
- 0 points — complete absence of movement (plegia or paralysis).
- 1 point — severe paresis: only minimal muscle contraction is visible without movement of the limb itself.
- 2 points — severe paresis: full range of motion is possible only with gravity eliminated (e.g., horizontal leg flexion).
- 3 points — moderate paresis.
- 4 points — mild paresis.
Special clinical tests are used to detect mild (latent) paresis.
Barré's sign is used for the arms. The patient sits, holds their arms out in front in supination, and closes their eyes. If central paresis is present, the weak arm begins to pronate and gradually drifts downward.
Mingazzini's test is designed for the legs. The patient lies prone with eyes closed, and their knees are flexed at a right angle. In the presence of muscle weakness, the lower leg on the affected side is not maintained in the set position and drops down.
Alteration of deep reflexes
The examination is performed using a neurological reflex hammer. Strikes are delivered with equal force on both sides. The main criteria of normal findings are symmetry and equal reflex response.
When the upper motor neuron (corticospinal tract) is damaged, reflex enhancement—hyperreflexia—is observed. This occurs when the lesion is located above the level of the reflex arc closure in the spinal cord. Conversely, a decrease (hyporeflexia) or loss (areflexia) indicates damage to the peripheral reflex loop.
Main deep reflexes and their levels of closure:
- Biceps tendon (m. biceps brachii, $C_V–C_{VI}$): arm flexed at a 70–110° angle. The strike is applied to the finger of the physician placed on the tendon. Response — forearm flexion.
- Triceps tendon (m. triceps brachii, $C_{VII}–C_{VIII}$): strike just above the olecranon (olecranon). Response — arm extension.
- Brachioradialis reflex (m. brachioradialis, $C_V–C_{VIII}$): strike on the radial styloid process (processus styloideus radii). Response — flexion and pronation.
- Knee jerk ($L_I–L_{IV}$): leg flexed at a 70–100° angle, strike on the patellar tendon. Response — lower leg extension.
- Ankle jerk ($S_I–S_{III}$): strike on the Achilles tendon. To activate (facilitate) the response, the physician may slightly stretch the tendon by performing passive dorsiflexion of the patient's foot.
If reflexes from the lower extremities cannot be elicited, the Jendrassik maneuver is used: the patient is asked to clasp their hands together and pull them apart forcefully.
Briefly: answers to topical questions
How is muscle strength assessed on the scoring scale?
Muscle strength and paresis severity are assessed on a point scale where 0 indicates paralysis and 4 indicates mild weakness.
- 4 points — mild paresis.
- 3 points — moderate paresis.
- 2 points — severe paresis (full range of motion is possible only with the elimination of gravity).
- 1 point — severe paresis (minimal movement or only visible muscle contraction without limb displacement).
- 0 points — complete absence of movement (plegia or paralysis).
How does central paresis differ from peripheral paresis?
Central and peripheral paresis differ in changes in muscle tone, deep reflex intensity, and the degree of muscle atrophy.
| Sign | Central paresis | Peripheral paresis |
|---|---|---|
| Muscle tone | Increased: spasticity, muscular hypertonia | Decreased: muscular hypotonia |
| Deep reflexes | Brisk, hyperreflexia, possible expansion of reflexogenic zones | Decreased, hyporeflexia or loss, areflexia |
| Pathological reflexes | Presence of pathological reflexes | Not specified in the cited sources |
| Muscle atrophy | May be absent in early stages; mild disuse atrophy develops later | Pronounced muscle hypotrophy, atrophy |
What pathological foot reflexes are characteristic of pyramidal tract lesions?
In pyramidal tract lesions, extensor and flexor pathological reflexes of the lower extremities are detected.
- Babinski reflex (Babinski reflex) — slow tonic extension of the great toe with fan-like spreading of digits II–V upon tactile stimulation of the lateral border of the sole.
- Oppenheim sign — extension of the great toe when stroking down the anterior surface of the tibia.
- Gordon sign — reflex extension of the great toe upon squeezing the calf muscle.
- Rossolimo reflex (Rossolimo reflex) — quick plantar flexion of the toes upon percussion of the distal phalanges of digits II–V.
Which superficial reflexes change when cortico-muscular pathways are damaged?
Damage to the cortico-muscular pathways (central paresis) results in the attenuation or complete loss of superficial exteroceptive reflexes.
The following cutaneous reflexes are altered:
- Abdominal reflexes (upper, middle, lower).
- Plantar reflex.
- Cremasteric reflex.
- Anal reflex.
Their reduction or loss indicates upper motor neuron damage.
To remember the classic Wernicke-Mann posture in central hemiparesis, the phrase "The hand begs, the leg sweeps" is used. It accurately describes the flexion and pronation of the arm combined with the extension of the leg.
Class and exam questions
How to detect latent paresis in the upper extremities?
The patient is asked to extend their arms forward in a supinated position and close their eyes (Barré's test). If central paresis is present, the affected arm will begin to pronate and drop.
What is the «clasp-knife» phenomenon?
This is a clinical sign of spasticity. During passive movement of the limb, the physician initially feels strong muscle resistance, which then abruptly drops.
What does the hyperactive tendon reflexes indicate?
Hyperreflexia indicates damage to the corticospinal (pyramidal) tract. The lesion is localized above the level of the reflex arc closure in the spinal cord.
Why is the Jendrassik maneuver needed?
It is used when tendon reflexes from the lower limbs cannot be elicited by standard methods. The patient hooks their fingers together and pulls them apart, which facilitates eliciting the reflex.
What else to study on this topic
- Topical diagnosis of reflex arc closure levels ($C_V–S_{III}$)
- Technique for eliciting the brachioradialis and biceps reflexes
- Assessment of superficial (cutaneous) abdominal and lower extremity reflexes
- Differential diagnosis of central and peripheral paresis
- Method for performing Mingazzini's test for the lower extremities
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