Myotonic syndrome

Myotonic syndrome is a phenomenon based on slow relaxation of muscles after their active contraction. Myotonic phenomenon is especially provoked by fast movement performed with considerable effort. After it, the relaxation phase is delayed for 5-30 seconds. With true myotonia, the patient experiences the greatest difficulties with the first movements; repeated movements are performed more freely and after some time they can normalize.

Thus, slow relaxation in myotonia is associated with increased tone, the reduction of which is significantly delayed. In a broad sense, myotonic syndrome is understood as any impaired relaxation of increased muscle tone that does not relate to either pyramidal or extrapyramidal hypertonus and can be either transient or permanent.

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Causes of myotonic syndrome

1. Thompson's myotonia and (less commonly) Becker's myotonia.
2. Eulenburg's paramyotonia.
3. Neuromyotonia (Isaacs syndrome).
4. Rigid person syndrome.
5. Encephalomyelitis with rigidity.
6. Dystrophic myotonia.
7. Schwartz-Jampel syndrome.
8. Psedomyotonia in hypothyroidism.
9. Tetanus (tetanus).
10. Pseudomyotonia in cervical radiculopathy.
11. Black widow spider bite.
12. Malignant hyperthermia.
13. Neuroleptic malignant syndrome.
14. Tetany.

Myotonia thompsonii

A classic example of myotonic syndrome is Thompson's myotonia, which is a hereditary disease with autosomal dominant (rarely autosomal recessive - Becker disease) inheritance and begins at any age, but most often in early childhood or adolescence. In an infant, the initial symptoms are usually noticeable to the mother: the first sucking movements are slow, and then become more energetic; after falling during play, the child cannot get up for a long time; in order to take an object from the child, it is necessary to forcibly unclench his fingers, etc. At school, the patient cannot immediately start writing or quickly get up from his desk and go to the board. These children do not participate in games that require quick movements. Cramps in the calf muscles are quite typical. Slow muscle relaxation is sometimes accompanied by their myotonic spasm. Passive movements and voluntary movements performed with little effort or slowly are not accompanied by myotonic spasm. Myotonic spasms can be observed in various groups: in the muscles of the arms and legs, neck, chewing, oculomotor, facial muscles, in the muscles of the tongue and trunk. Cold increases the manifestations of myotonia; alcohol alleviates. The state of tonic spasm in myotonia is measured in seconds in most cases and almost never lasts more than one or two minutes. Quite often, patients complain of pain in various parts of the body.

Thompson's myotonia is characterized by an athletic build and marked hypertrophy (sometimes more or less selective in location) of the striated muscles. A valuable test for detecting myotonia is walking up stairs. When walking on a level floor, difficulties arise especially often after a long period of rest, as well as when changing the pace or nature of movement. Myotonic spasms in the hands make writing, shaking hands and other manipulations difficult. The myotonic phenomenon may manifest itself in articulation when pronouncing the first few words (slurred speech); during swallowing (first swallowing movements). Sometimes the first chewing movements are difficult, etc. In some patients, myotonic spasm is observed in the orbicularis oculi muscles. An attempt to open the eyes after squinting tightly is difficult; the resulting spasm is eliminated gradually, sometimes after 30-40 seconds.

A characteristic manifestation of myotonia is an increase in the mechanical and electrical excitability of muscles: the so-called "percussion myotonia" and "myotonic phenomenon" in EMG studies. When struck with a neurological hammer, a characteristic depression is formed at the site of the blow, noticeable in the deltoid, gluteal, thigh and calf muscles, and especially in the muscle of the tongue. The simplest phenomenon is the adduction of the thumb when striking the eminence of the thumb with a hammer. Another clear sign is a sharp clenching of the fingers into a fist, after which the patient cannot immediately unclench it. The duration of the myotonic "pit" reflects the severity of myotonia as a whole. It has been noted that after sleep, myotonic symptoms can temporarily intensify. The course of the disease after the initial period of increase is generally stationary.

The so-called remittent myotonia (myotonia that intensifies with excess potassium) has also been described; its clinical manifestations are similar to Thompson's disease. Myotonia is generalized, manifesting itself in the facial muscles as well. Fluctuations in the severity of myotonia from day to day are characteristic (increasing after intense physical exertion or after the intake of large amounts of potassium with food). The myotonic phenomenon is revealed on EMG; no pathology is found in muscle biopsy.

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Paramyotonia Eulenburg

Eulenburg's paramyotonia is a rare autosomal dominant disorder called congenital paramyotonia. Patients feel healthy when not cooled. Well-developed muscles and increased mechanical excitability of muscles (a "pit" in the tongue, a thumb symptom) are often detected. After general cooling (rarely after local cooling), a muscle spasm develops, reminiscent of myotonic. The facial muscles are primarily involved (the orbicularis oculi, oris, chewing, and sometimes the extraocular muscles). Involvement of the muscles of the distal parts of the hands is also characteristic. As with myotonia, after a sharp contraction of these muscles, there is a sharp difficulty in relaxing. However, unlike Thompson's myotonia, with repeated movements this spasm does not decrease, but, on the contrary, intensifies (stiffness).

Most patients soon develop paresis and even paralysis of the affected muscles after muscle spasm, lasting from several minutes to several hours or even days. These paralyses develop against the background of hypokalemia or hyperkalemia. Very rarely, patients with congenital paramyotonia exhibit constant muscle weakness and atrophy. Muscle biopsy reveals mild signs of myopathy. Enzyme activity in the blood is normal.

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Neuromyotonia

Neuromyotonia (Isaacs syndrome, pseudomyotonia, syndrome of constant muscle fiber activity) begins at any age (usually at 20-40 years) with a constant increase in muscle tone (stiffness) in the distal parts of the arms and legs. Gradually, the process spreads to the proximal parts of the limbs, as well as the muscles of the face and pharynx. The muscles of the trunk and neck are involved less often and to a lesser extent. As a result of constant muscle hypertonicity, which does not disappear during sleep, flexor muscle contractures begin to form. Constant large slow fascicular twitching (myokymia) in the muscles of the arms and legs is characteristic. Active movements can increase muscle tension (resembling spasms). Mechanical excitability of muscles is not increased. Tendon reflexes are reduced. The disease slowly progresses with a tendency for the process to generalize. Gait in a constrained rigid manner - "armadillo" gait. EMG - spontaneous irregular activity at rest.

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Rigid person syndrome

Stiff-man syndrome typically begins in the third or fourth decade of life with an insidious onset of stiffness in the axial musculature, particularly in the neck and lower back. Gradually, muscle tension spreads from the axial to the proximal muscles. In advanced stages, there is a tendency (rarely) to involve the distal extremities and, occasionally, the face. Symmetrical, constant muscle tension is usually found in the extremities, trunk, and neck; the muscles are firm to palpation. Rigidity of the abdominal wall and paraspinal muscles leads to a characteristic fixed hyperlordosis in the lumbar region, which persists at rest. This postural phenomenon is so typical that in its absence the diagnosis should be questioned. Movement is difficult due to severe rigidity. Tension in the chest muscles can make breathing difficult.

Against the background of muscle rigidity, any sudden stimuli of a sensory or emotional nature provoke painful (painful) muscle spasms. Provoking stimuli may include unexpected noise, sharp sounds, active and passive movements in the limbs, touch, fear, and even swallowing and chewing. Rigidity decreases during sleep, anesthesia, and the administration of benzodiazepine or baclofen. However, even during sleep, hyperlordosis is not eliminated, which can be very pronounced (the doctor's hands freely pass under the paraspinal muscles when the patient is lying down).

Approximately one third of patients with rigid person syndrome develop type I diabetes mellitus and other autoimmune diseases (thyroiditis, myasthenia, pernicious anemia, vitiligo, etc.), which allows us to presumably classify this disease as autoimmune. This is also confirmed by the fact that 60% of patients have a very high titer of antibodies to glutamic acid decarboxylase.

A variant of the rigid-man syndrome is the "jerk stiff-man syndrome", in which, in addition to constant muscle tension, rapid, pronounced (night and day) myoclonic jerks of the axial and proximal muscles of the limbs are observed. Myoclonic jerks usually appear against the background of a disease that has existed for several years and respond to diazepam. These patients often have stimulus-sensitive myoclonus.

Differential diagnosis is performed with Isaacs syndrome, in which myokymia is detected on EMG. Sometimes it is necessary to exclude spasticity in pyramidal syndrome (however, in rigid-person syndrome there are no high reflexes) and rigidity in progressive supranuclear palsy (here there are symptoms resembling Parkinsonism and dystonia). Severe muscle spasms often force us to differentiate the disease from tetanus, but trismus is not characteristic of rigid-person syndrome. Electromyography allows us to differentiate this syndrome not only from Isaacs syndrome, but also from various types of myopathy and muscular dystrophy.

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Progressive encephalomyelitis with rigidity

Progressive encephalomyelitis with rigidity (or "subacute myoclonic spinal neuronitis") also presents with rigidity of axial and proximal muscles and painful muscle spasms, which are also provoked by sensory and emotional stimuli. Mild pleocytosis in the cerebrospinal fluid is possible. In the neurological status, mild cerebellar ataxia is sometimes detected as the disease progresses. MRI can exclude this disease.

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Dystrophic myotonia

Dystrophic myotonia (or myotonic dystrophy) is probably the most common form of myotonia and is characterized by three main syndromes:

1. myotonic type of movement disorder;
2. myopathic syndrome with a characteristic distribution of amyotrophies (damage to the muscles of the face, neck, distal parts of the arms and legs);
3. involvement of the endocrine, autonomic and other systems in the process (multisystemic manifestations).

The age of onset of the disease and its manifestations are very variable. Myotonic disorders are more pronounced in the flexors of the fingers (grasping objects is most difficult); with repeated movements, the myotonic phenomenon decreases and disappears. Weakness and muscle atrophy, as a rule, appear later. They affect the muscles of the face, especially the masticatory muscles, including the temporal, sternocleidomastoid muscles and the muscles that raise the upper eyelid, the perioral muscles; a typical appearance develops: amimia, half-drooping eyelids, accentuated temporal fossae, diffuse atrophy of the facial muscles, dysarthria and a low, dull voice. Atrophy of the distal parts of the arms and the peroneal muscle group on the legs is often noted.

Cataracts are typical; in men - testicular atrophy and impotence; in women - infantilism and early menopause. In 90% of patients, some abnormalities are detected on the ECG, mitral valve prolapse, and gastrointestinal tract motor dysfunction. MRI often reveals cortical atrophy, ventricular dilation, focal changes in the white matter, and abnormalities in the temporal lobes. Hyperinsulinemia is often detected. The CPK level is usually normal. EMG shows characteristic myotonic discharges. Muscle biopsy shows various histological abnormalities.

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Schwartz-Jampel syndrome

Schwartz-Jampel syndrome (chondrodystrophic myotonia) begins in the first year of life and is manifested by a sharp difficulty in relaxing contracted muscles in combination with increased mechanical and electrical excitability of the muscles. Sometimes spontaneous muscle contractions and cramps are observed. Some muscles are hypertrophied and dense upon palpation at rest. Painful contractions are observed in the limbs, abdominal muscles, and in the face (myotonic blepharospasm; painful contractions of the muscles of the larynx, tongue, pharynx, which can sometimes cause asphyxia). Very often, various skeletal anomalies are detected - dwarfism, short neck, kyphosis, scoliosis, facial asymmetry, retrognathia, etc. As a rule, there is a delay in mental development. EMG - myotonic discharges.

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Pseudomyotonia in hypothyroidism

This syndrome is manifested by slow contraction and equally slow relaxation of muscles, which is clearly revealed already when evoking tendon reflexes, especially the Achilles reflex. The muscles are edematous. There are no typical myotonic discharges on EMG; aftereffect potentials are sometimes visible after voluntary contraction. Timely diagnosis of hypothyroidism is important for recognizing pseudomyotonia in hypothyroidism.

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Tetanus

Tetanus is an infectious disease. Trismus ("jaws locked") is the first symptom of tetanus in 80% of cases. Following trismus, and sometimes simultaneously with it, there is tension in the muscles of the back of the head and contraction of the muscles of the face (facies tetanica): the forehead wrinkles, the eye slits narrow, the mouth stretches into a laughing grimace ("sardonic smile"). One of the cardinal signs of tetanus is dysphagia. With increasing tension in the occipital muscles, it first becomes impossible to tilt the head forward, then the head is thrown back (opisthotonus). Spasm of the back muscles develops; the muscles of the trunk and abdomen are tense, becoming very prominent. The abdomen acquires a board-like hardness, abdominal breathing is difficult. If the rigidity also affects the limbs, then in this position the patient's entire body can acquire the shape of a column (orthotonus), which is how the disease got its name. The spasms are very painful and occur almost continuously. Any external stimuli (touch, knock, light, etc.) provoke general tetanic spasms.

In addition to generalized tetanus, so-called local tetanus (“facial paralytic tetanus”) has also been described.

Differential diagnosis of tetanus is carried out with tetany, rabies, hysteria, epilepsy, meningitis, and strychnine poisoning.

Pseudomyotonia in cervical radiculopathy

This is a rare syndrome observed with damage to the C7 root. Such patients complain of difficulty opening the hand after grasping an object. Palpation of the hand reveals muscle tension ("pseudomyotonia"), which occurs due to paradoxical contraction of the finger flexors when attempting to activate the finger extensors.

A Black Widow spider bite may be accompanied by increased muscle tone, twitching, and cramping in the area of the bite.

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Malignant hyperthermia

Malignant hyperthermia is a hereditary disease transmitted in an autosomal dominant manner, which is based on increased sensitivity to some substances used for anesthesia. There is a slow (hours) or rapid rise in body temperature, tachycardia, arrhythmia, tachypnea, muscle fasciculations, increased muscle tone. Generalized muscle rigidity and severe metabolic acidosis, myoglobinuria develop. Without treatment, epileptic seizures develop and death may occur. The diagnosis is not difficult, since there is a clear connection with anesthesia. The level of CPK exceeds normal values by about 10 times.

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Neuroleptic malignant syndrome (NMS)

NMS is a dangerous complication of neuroleptic therapy, manifested by hyperthermia, muscle rigidity and increased levels of CPK. The syndrome is usually accompanied by disturbances of consciousness (confusion, stupor) and autonomic disorders: tachycardia, arrhythmia, hyperhidrosis. The most frequent and dangerous complication is rhabdomyolysis, which manifests itself in acute diffuse breakdown of muscle tissue, leading to extremely high levels of CPK, hyperkalemia, myoglobinemia and acute renal failure, requiring temporary dialysis.

In the differential diagnosis of neuroleptic malignant syndrome, it is recommended to exclude other possible causes of rhabdomyolysis (compression injuries, alcohol abuse, heat stroke, prolonged immobilization), as well as malignant hyperthermia, severe dystonic spasms, lethal catatonia, serotonin syndrome.

Sometimes neuroleptic malignant syndrome must be differentiated from infectious lesions of the central nervous system, allergic reactions to drugs, hyperthyroidism, tetany, and even Parkinson's disease.

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Tetany

Tetany reflects overt or latent parathyroid gland insufficiency (hypoparathyroidism) and is manifested by a syndrome of increased neuromuscular excitability. The overt form is observed in endocrinopathy and occurs with spontaneous muscle cramps. The latent form is most often provoked by neurogenic hyperventilation (in the picture of permanent or paroxysmal psychovegetative disorders) and is manifested by paresthesia in the limbs and face, as well as selective muscle cramps ("carpopedal spasms", "obstetrician's hand") and emotional disorders. Trismus and spasm of other facial muscles may be observed. In severe cases, the muscles of the back, diaphragm and even the larynx (laryngospasm) may be involved. The Chvostek symptom and the Trousseau-Bahnsdorff symptom and other similar symptoms are revealed. Low calcium levels (there are also normocalcemic neurogenic variants) and increased phosphorus levels in the blood are also possible.

Differential diagnosis: it is necessary to exclude diseases of the parathyroid glands, autoimmune processes, psychogenic disorders of the nervous system.

Diagnostic tests for myotonic syndrome

General and biochemical blood tests, urine tests, studies of electrolyte levels and CPK in the blood; determination of the level of hormones of the thyroid and parathyroid glands; EMG; study of the speed of excitation conduction along the nerve; muscle biopsy; study of the myotonic phenomenon (clinically and electromyographically); genetic analysis and other, as indicated, diagnostic studies (cerebrospinal fluid, somatosensory evoked potentials, MRI of the spinal cord and spine, etc.).

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