Violation of muscle tone

Muscle tone is defined as the residual muscle tension during their relaxation or as a resistance to passive movements in the case of voluntary muscle relaxation ("arbitrary denervation"). Muscle tone depends on factors such as the elasticity of muscle tissue, the state of the neuromuscular synapse, peripheral nerve, alpha and gamma motoneurons and spinal cord interneurons, as well as supraspinal influences from cortical motor centers, basal ganglia, facilitating and inhibitory systems of the middle brain, reticular formation of the brainstem, cerebellum and vestibular apparatus.

The tonus is thus a reflex phenomenon, which is provided by both afferent and efferent components. Muscle tone also has an involuntary regulatory component that takes part in postural reactions, physiological synkinesia, and coordination of movements.

Muscle tone can change in diseases and injuries at different levels of the nervous system. Interrupting the peripheral reflex arc leads to atony. Reduction of supraspinal influences, which usually inhibit spinal reflex systems, leads to its increase. The imbalance of descending facilitating and inhibitory influences can either reduce or increase muscle tone. It is influenced, but to a lesser extent, by a mental state and arbitrary regulation.

In clinical examination, it must be remembered that muscle tone can sometimes be difficult to assess, since the only reliable instrument for measuring it remains the doctor's impressions when examining passive movements. It is influenced by the ambient temperature (the cold increases, and the heat reduces the muscle tone), the speed of passive movements, the changing emotional state. Much depends on the experience of the doctor, who also happens to be different. Difficult cases require repeated studies of muscle tone in the lying position of the patient, the use of special tests (shaking test for the shoulders, head drop test, leg swing test, pronation-supination, and others). It is useful not to rush with categorical assessments of tone in unclear, diagnostically difficult cases.

The main types of muscle tone disorders:

I. Hypotension

II. Hypertension

1. Spasticity.
2. Extrapyramidal rigidity.
3. The phenomenon of confrontation (gegenhalten).
4. Catatonic rigidity.
5. Decortication and decerebration rigidity. Hormetonia.
6. Myotonia.
7. Tension of muscles (Stiffness).
8. Reflex hypertension: muscular-tonic syndromes in diseases of the joints, muscles and spine; stiff neck muscles with meningitis; increased muscle tone in peripheral trauma.
9. Other types of muscle hypertension.
10. Psychogenic muscle hypertension.

I. Hypotension

Hypotension is manifested by a decrease in muscle tone below the normal physiological level and is most typical for injuries at the spinal-muscular level, but it can also be observed in diseases of the cerebellum and some extrapyramidal disorders, especially with chorea. Increased volume of movements in the joints (perezbibanie them) and the amplitude of passive excursions (especially in children). Atony does not hold the prescribed posture of the limb.

The diseases affecting the segmental level of the nervous system include poliomyelitis, progressive spinal amyotrophy, syringomyelia, neuropathies and polyneuropathies, as well as other diseases in which the anterior horns, posterior columns, rootlets and peripheral nerves are involved. In the acute phase of the transverse lesion of the spinal cord, a spinal shock develops, in which the activity of the cells of the anterior horns of the spinal cord and spinal reflexes temporarily slows down below the level of the lesion. The upper level of the cerebrospinal axis, whose dysfunction can lead to atony, is the caudal sections of the brainstem, the involvement of which in a deep coma is accompanied by a complete atony and heralds a bad coma outcome.

Muscle tone can be reduced with cerebellar lesions of different types, more often, akinetic epileptic seizures, deep sleep, during fainting, states of disturbed consciousness (fainting, metabolic coma) and immediately after death.

At attacks of a cataplexy, usually connected with a narcolepsy, besides weakness the muscular atony develops. Attacks are often provoked by emotional stimuli and are usually accompanied by other manifestations of polysymptomatic narcolepsy. Rarely, cataplexy is a manifestation of a midbrain tumor. In the acute ("shock") phase of the stroke, the paralyzed limb sometimes detects hypotension.

A separate problem is hypotension in infants (a "sluggish child"), the causes of which are very diverse (stroke, Down syndrome, Prader-Willi syndrome, birth trauma, spinal muscular atrophy, congenital neuropathy with hypomyelinization, congenital myasthenic syndromes, infant botulism, congenital myopathy, benign congenital hypotension).

Rarely post-stroke hemiparesis (with isolated lesion of the lentiform nucleus) is accompanied by a decrease in muscle tone.

II. Hypertension

Spasticity

Spasticity develops in any lesions of cortical (upper) motoneuron and (predominantly) cortico-spinal (pyramidal) tract. In the genesis of spasticity, imbalance of inhibitory and facilitating influences from the reticular formation of the midbrain and brainstem is important, followed by an imbalance of the alpha and gamma motoneurons of the spinal cord. The phenomenon of a "folding knife" is often revealed. The degree of hypertonia can vary from mild to severe, when the doctor is unable to overcome spasticity. Spasticity is accompanied by tendon hyperreflexia and pathological reflexes, clones and, sometimes, protective reflexes and pathological syncinesies, as well as a decrease in surface reflexes.

With hemiparesis or hemiplegia of cerebral origin, spasticity is most pronounced in the flexor muscles on the arms and extensors - on the legs. In bilateral cerebral (and some spinal) injuries, spasticity in the adductor muscles of the hip leads to characteristic dysbasia. With relatively coarse spinal injuries in the legs, a flexor spasm of muscles, reflexes of spinal automatism and flexor paraplegia are more often formed.

Extrapyramidal rigidity

Extrapyramidal rigidity is observed in diseases and injuries affecting the basal ganglia or their connections to the middle brain and the reticular formation of the brain stem. The increase in tone concerns both flexors and extensors (an increase in muscle tone by plastic type); resistance to passive movements is noted for limb movements in all directions. The severity of rigidity may be different in the proximal and distal parts of the limbs, in the upper or lower part of the body, as well as in the right or left half of the body. At the same time, the phenomenon of "gear wheel" is often observed.

The main causes of extrapyramidal rigidity: rigidity of this type is most often observed in Parkinson's disease and other parkinsonian syndromes (vascular, toxic, hypoxic, post-encephalitic, post-traumatic and others). In this case, there is a tendency to gradually involve all muscles, but the muscles of the neck, trunk and flexors are more coarse. Muscle rigidity is combined here with symptoms of hypokinesia and (or) a tremor of rest of low frequency (4-6 Hz). Characteristic also postural disorders of varying severity. Rigidity on one side of the body increases with the performance of active movements with contralateral limbs.

Less often, plastic hypertension is observed in tonic forms of dystonic syndromes (debut of generalized dystonia, tonic form of spastic torticollis, dystonia of the foot, etc.). This type of hypertonia sometimes causes serious difficulties in carrying out a syndromic differential diagnosis (parkinsonism syndrome, dystonic syndrome, pyramidal syndrome). The most reliable way to recognize dystonia is to analyze its dynamism.

Dystonia (a term not intended to refer to a muscle tone, but for a specific type of hyperkinesia) is manifested by muscle contractions that lead to characteristic postural (dystonic) phenomena.

The phenomenon of confrontation

The phenomenon of confrontation or hegenhalten is manifested by increasing resistance in any passive movements in all directions. The doctor at the same time makes every effort to overcome the resistance.

The main reasons: the phenomenon is observed in the lesions of corticospinal or mixed (corticospinal and extrapyramidal) pathways in the anterior (frontal) regions of the brain. The predominance of this symptom (as well as the grasping reflex) on one hand indicates a bilateral lesion of the frontal lobes with predominance of damage in the contralateral hemisphere (metabolic, vascular, degenerative and other pathological processes).

Catatonic rigidity

There is no generally accepted definition of catatonia. This form of increasing muscle tone in many respects is analogous to extrapyramidal rigidity and, probably, has some overlapping pathophysiological mechanisms with it. The phenomenon of "wax flexibility", preset "frozen postures" (catalepsy), "strange motor skills" against the background of gross mental disorders in the picture of schizophrenia is characteristic. Catatonia is a syndrome that has not yet received a clear conceptual design. It is unusual in that it blurs the line between psychiatric and neurological disorders.

The main reasons: catatonia syndrome is described in the case of non-convulsive forms of epileptic status, and also with some gross organic lesions of the brain (brain tumor, diabetic ketoacidosis, hepatic encephalopathy), which, however, needs further clarification. Usually it is characteristic for schizophrenia. Within the framework of schizophrenia, catatonia manifests itself as a complex of symptoms, including mutism, psychosis and unusual motor activity, which varies from flare-ups to stupor. Concomitant manifestations: negativism, echolalia, echopraxia, stereotypes, mannerisms, automatic obedience.

Decortication and decerebration rigidity

Decerebral rigidity manifests a constant stiffness in all extensors (anti-gravity muscles), which can sometimes increase (spontaneously or with pain stimulation in a comatose patient), manifested by forced extension of arms and legs, their reduction, easy pronation and trism. Decortication rigidity manifests itself in the flexion of the elbow joints and wrist bands with the extension of the legs and feet. Decerebral rigidity in patients in coma ("extensor postural postures", "extensor postural reactions") have a worse prognosis compared to decortic rigidity ("flexor pathological poses").

Similar generalized rigidity or spasticity with retraction (extension) of the neck and, sometimes, the trunk (opisthotonus) can be observed with meningitis or meningism, tonic phase of epileptic seizure and in processes in the posterior cranial fossa occurring with intracranial hypertension.

The variant of extensor and flexor spasms in a patient in a coma is the rapidly changing muscle tone in the limbs (germetonia) in patients in the acute phase of hemorrhagic stroke.

Myotonia

Congenital and acquired types of myotonia, myotonic dystrophy, paramyotonia and, sometimes, myxedema are manifested by increased muscle tone, which is revealed, as a rule, not with passive movements, but after active arbitrary contraction. With paramyotonia, a marked increase in muscle tone is provoked by cold. Myotonia is detected in a sample of finger tightening into the fist, manifested by delayed relaxation of spasmodic muscles; repeated movements lead to a gradual recovery of normal movements. Electrical stimulation of the muscles causes their increased contraction and delayed relaxation (the so-called myotonic reaction). Percussion (hammer blow) of the tongue or tenar reveals a characteristic myotonic phenomenon - a "dimple" in the place of impact and bringing of the thumb with delayed muscle relaxation. Muscles can be hypertrophied.

Tension of muscles (stiffness)

Tension of muscles is a special group of syndromes, linked by its pathogenesis mainly with spinal (interneurons) or peripheral lesions (syndromes of "hyperactivity of motor units").

Isaac's syndrome (neuro-myotonia, pseudomonotonia) is manifested by stiffness, which first appears in the distal parts of the limbs and gradually spreads to the proximal, axial and other muscles (face, bulbar musculature) with difficulty of movement, dysbasia and permanent myocamia in the affected muscles.

The stiff-person syndrome, on the other hand, begins with the rigidity of axial and proximal muscles (mainly the muscles of the pelvic girdle and trunk) and is accompanied by characteristic spasms of high intensity, in response to external stimuli of different modalities (an intensified start-reaction) .

Close to this group of musculoskeletal disorders are Mac-Ardl's disease, paroxysmal myoglobulinemia, tetanus (tetanus).

Tetanus is an infectious disease manifested by generalized muscle rigidity, although the muscles of the face and lower jaw are involved earlier than others. This background is characterized by muscle spasms that arise spontaneously or in response to tactile, auditory, visual and other stimuli. Between spasms the expressed generalized rigidity

"Reflex" rigidity

"Reflex" stiffness combines muscular-tonic tension syndromes in response to painful irritation in joints, spine and muscle diseases (for example, muscular tension in appendicitis, myofascial syndromes, cervicogenic headaches, other vertebrogenic syndromes, and muscle tone in peripheral trauma).

Other types of muscle hypertension include muscle rigidity during epileptic seizures, tetany, and some other conditions.

High muscle tone is observed during the tonic phase of generalized convulsive seizures. Sometimes purely tonic epileptic seizures without a clonic phase are observed. The pathophysiology of this hypertonia is not fully understood.

Aetania is manifested by a syndrome of increased neuromuscular excitability (symptoms of Khvostek, Tissaur, Erba, etc.), carp-pedal spasms, paresthesia. More often there are variants of latent tetany against the background of hyperventilation and other psycho-vegetative disorders. A rare cause is endocrinopathy (hypoparathyroidism).

Psychogenic hypertension

Psychogenic hypertension is most clearly manifested in the classical picture of a psychogenic (hysterical) seizure (pseudo-fit) with the formation of a "hysterical arc," with a pseudo-dystonic version of psychogenic hyperkinesis, and also (less often) in the picture of the lower pseudoparapause with pseudo-hypertonus in the feet.

Diagnosis of muscle tone disorders

EMG, determination of the rate of excitation on the nerve, general and biochemical analysis of blood, electrolytes in blood, CT or MRI of the brain, investigation of cerebrospinal fluid. You may need: muscle biopsy, CK in the blood, consultation of an endocrinologist, a psychiatrist.

[1], [2], [3], [4], [5], [6], [7]