Weakness in performing physical exertion (pathological muscle weakness)

Muscular fatigue can be caused not only by the defeat of the neuromuscular synapse (immune-dependent myasthenia gravis and myasthenic syndromes), but also by common internal diseases without direct damage to the neuromuscular system, such as chronic infections, tuberculosis, sepsis, Addison's disease or malignant diseases. Weakness is usually combined with the specific symptoms of the underlying disease; general clinical and physical examination in these cases is the most important for diagnosis.

The main causes of muscle fatigue when performing physical exertion:

1. Myasthenia gravis.
2. Lambert-Eaton Syndrome.
3. Hereditary (congenital) myasthenic syndromes.
4. Poliomyositis.
5. Multiple sclerosis (early stages).
6. OVDP (Guillain-Barre syndrome).
7. Endocrinopathies.
8. Botulism.
9. Glycogenosis (Mack Ardla disease).
10. Disorders of potassium metabolism.
11. Metabolic disorders of calcium.
12. Mental disorders (asthenia and depression).
13. Chronic fatigue syndrome.
14. Cudogenous intermittent claudication.
15. Iatrogenic myasthenic syndrome (drug).

Myasthenia gravis

It is well known that physical exercise fatigue (pathological muscle fatigue) is the main complaint of patients suffering from myasthenia gravis, immune-dependent myasthenia gravis. At the beginning of the disease, weakness is completely absent in the morning hours after an overnight rest, patients find a decrease in muscle strength in various activities - depending on the muscles or muscle groups involved in these activities: reading, speaking, walking, stereotyped hands, stereotyped foot movements for example, typing on a typewriter, pressure on the pedal of the machine). Rest allows (at least in part) to restore muscle strength. Weakness is most pronounced in the evening.

If suspected of myasthenia gravis, a simple clinical trial is needed to detect abnormal muscular fatigue - the patient is asked 30-40 times (or less) to perform those movements that suffer. For example, closing and opening the eyes (with the myasthenia), loud counting, raising the head in a supine position on the back, squeezing the fingers of the hand into a fist, etc. (with the generalized limb-belt myasthenia gravis). The indicator muscle when performing a test for myasthenia gravis is m. Triceps. If a decrease in muscle strength occurs during this test (or a loss of voice), then pharmacological tests are necessary. Intramuscular injections of anticholinesterase drugs (eg, proserin) restore muscle strength after 30 seconds - 2 minutes for a period of several minutes to half an hour. The longer the recovery period, the less it is typical for myasthenia gravis, and should be the basis for continuing the diagnostic search. It should be borne in mind the possibility of developing the patient's expressed side effects of the anticholinesterase drug and be prepared for the product of atropine injection.

To exclude the psychogenic nature of muscle weakness, it is recommended to do an intravenous injection of saline.

With electrical stimulation of the peripheral nerve, the action potentials in the corresponding muscle decay; this effect is reversed by the anticholinesterase drug or substances acting on the postsynaptic membrane.

When making the diagnosis of myasthenia gravis, further research is needed. Blood should be examined for the presence of antibodies to acetylcholine receptors and skeletal muscles. Studies are also needed for the possible presence of thymoma or the persistent functioning of the thymus, which has not undergone timely involution. Myasthenic weakness can also develop in hyperthyroidism, systemic lupus erythematosus, Sjogren's disease, polymyositis, rheumatoid arthritis, in the debut stage of multiple sclerosis.

Lambert-Eaton Syndrome

Lambert-Eaton syndrome is a paraneoplastic syndrome in which pathological muscle fatigue can resemble a myasthenic syndrome. Nevertheless, the observed muscular fatigue has distinctive features that allow to differentiate myasthenia gravis and myasthenic Lambert-Eaton syndrome. Weakness does not begin with the outer eye or facial muscles, as is the case with myasthenia gravis; moreover, these muscles with Lambert-Eaton syndrome often remain intact. The muscles of the pelvic or shoulder girdle are the most involved. Although patients complain of weakness during physical exertion, a clinical study reveals that with repeated contractions of the involved muscles, their strength first increases and decreases only after a minute or more. This phenomenon is also noted in the EMG study: the amplitude of the action potential first increases and then decreases. Pharmacological tests give a minimal effect or negative. The syndrome is more common in men. At the heart of the disease, lung carcinoma lies in 70% of cases.

Hereditary (congenital) myasthenic syndromes

In the literature, periodically there are descriptions of benign congenital myopathy, in which myasthenic manifestations can be observed in the neonatal period or in the next subsequent period. These are non-progressive forms of myopathy; their manifestations remain stable throughout life; sometimes they progress slightly, in others they even have a regressive course (central stem disease, non-myeloid myopathy, tubular myopathy, etc.). It is almost impossible to differentiate these diseases from the clinical picture (usually a "floppy baby" is diagnosed). An electron-microscopic picture characteristic of this or that form is revealed.

On the other hand, true congenital myasthenic syndromes are described, each of which is distinguished by a unique defect in the cholinergic synapse (peculiarities of the structure of presynaptic terminals, postsynaptic receptors, violations of the acetylcholine kinetics, etc.). Even in newborns, symptoms such as progressive ptosis, bulbar and respiratory disorders in crying are noted. Later, these symptoms are joined by fluctuating paralysis of the oculomotor muscles, fatigue during movements. In some cases, myasthenic symptoms become clinically noticeable only in the second or third decade of life (slow-channel syndrome). All congenital myasthenic syndromes are inherited in an autosomal recessive manner.

Poliomyositis

Poliomyositis is manifested by the gradual development of symmetrical proximal muscle weakness, myalgic syndrome, early swallowing disorder. Usually there is a rise in CK in the serum, changes in EMG (potentials of fibrillation, positive waves, reduction of the duration of potentials of motor units), increased ESR. In addition to muscle weakness, fatigue can occur during exercise.

Multiple sclerosis

In the early stages of multiple sclerosis, complaints of fatigue with physical exertion are possible. The cause of fatigue remains unknown. The revealed symptoms in the form of characteristic paresthesia, visual, pyramidal and cerebellar symptoms, indicating multifocal lesion of the central nervous system, leave no doubt for the diagnosis.

OVDP (Guillain-Barre syndrome)

In the early stages of acute inflammatory demyelinating polyneuropathy Guillain-Barre, there may be increased fatigue on physical exertion with mild or subclinical manifestations of polyneuropathy. The development of a typical clinical picture of polyneuropathy removes diagnostic issues.

Endocrinopathies

Some endocrinopathies may include myasthenopodic manifestations in their clinical manifestations: hypothyroidism (characterized by cold, pale, dry skin, lack of cravings, constipation, thickening of the tongue, hoarse voice, bradycardia, muscle swelling, slowing of achilles reflexes, etc., rarely accompanied by other neurological symptoms such as paresthesia, ataxia, carpal tunnel syndrome, krampi); hyperthyroidism (typical proximal muscle weakness with difficulty getting up from the squatting position, sweating, tachycardia, tremor, hot skin, heat, diarrhea intolerance, etc., neurological symptoms such as pyramidal marks are rarely noted); hypoparathyroidism (muscular weakness and cramps, tetany, headaches, fatigue, ataxia, convulsive seizures, rarely hallucinations and choreoathetoid symptoms); hyperparathyroidism (differs true myopathy with muscular atrophies, depression, emotional lability, irritability, confusion, constipation); Cushing's disease, hypopituitarism, diabetes mellitus. All these diseases are characterized by complaints of fatigue, which sometimes becomes noticeable. With Addison's disease and Symonds disease, fatigue becomes one of the main manifestations.

Botulism

Botulism - severe intoxication, resulting from eating foods containing toxins sticks of Clostridium botulinum. Botulinum toxin is a powerful poison blocking the release of acetylcholine from presynaptic endings. Progressive muscular fatigue and weakness often begin with ocular motility (incomplete or total external and internal ophthalmoplegia) and pharyngeal muscles with subsequent generalization (diplopia, ptosis, dysarthria, dysphagia, symmetrical weakness of the muscles of the extremities and respiratory muscles). Usually, the pupils are dilated and there are no pupillary reactions, but consciousness is not disturbed. In severe cases, respiratory muscles are involved. Symptoms of a generalized disorder of the cholinergic transmission may be observed: poorly reacting pupils, dry mouth, intestinal paresis ("paralytic ileus") and, sometimes, bradycardia.

The diagnosis is confirmed if, when a laboratory mouse is injected with a patient's serum or infected food, it shows signs of disease.

Glycogenoses

All types of glycogenases, especially Mc-Ardl's disease (insufficiency of muscle phosphorylase), can be accompanied by muscle fatigue during physical exertion. A characteristic sign of insufficiency of muscle phosphorylase is the pain and tension in muscles that occur in young people during physical work. After loading, the lactate content in the blood does not increase. Perhaps the development of contractures with electromyographic silence in the affected muscles. A muscle biopsy reveals an increase in glycogen content.

Disorders of potassium metabolism

These disorders can manifest, in addition to muscle fatigue, three paroxysmally occurring syndromes of muscle weakness: familial hypokalemic paralysis, hyperkalemic periodic paralysis, and normokaliemic periodic paralysis.

Periodic hypokalemic paralysis (paroxysmal myoplegia)

Violation of potassium metabolism in muscle tissue causes paroxysmal hypokalemic paralysis. The leading symptom is the periodic paralysis of muscles of the trunk and extremities, lasting for hours. As a rule, the facial muscles and the diaphragm remain uninvolved. Most seizures occur at night without any specific reason. The provoking factor can be physical stress. Attacks can also be provoked by eating foods rich in carbohydrates.

During an attack, there is a dramatic decrease in the concentration of potassium in the plasma, which sometimes reaches 2-1.7 mmol / l; a "silent" EMG can be recorded; EMG does not have spontaneous activity or action potentials. With less intense attacks, the amplitude of action potentials is low, and their duration is reduced.

If the diagnosis is uncertain, the attack can be provoked with a diagnostic purpose by oral intake of a high-dose glucose patient in combination with a subcutaneous injection of 20 units of insulin.

A normokaliemic variant of periodic paralysis is also described.

Severe hypokalemia (less than 2.5 mmol / l) can lead not only to fatigue, but also to pronounced sluggish tetraplegia. The main reasons are: Conn's syndrome (aldosterone-secreting adrenal tumor), renal failure, enteritis and severe diarrhea, excessive diuretic therapy, alcoholism, lithium intoxication, mineralocorticoid effect, thyrotoxicosis.

The expressed hyperkalemia (more than 7 mmol / l) can lead to severe tetraplegia with an ascending current, reminiscent of Guillain-Barre syndrome. The most common causes are renal failure, adrenal insufficiency, rhabdomyolysis, excessive intravenous administration of potassium, administration of aldosterone antagonists.

Metabolic disorders of calcium

Chronic hypocalcemia (primary or secondary hypoparathyroidism, kidney disease), in addition to muscle fatigue, can cause tetanic attacks and a noticeable muscle weakness. In infants, hypocalcemia can lead to even convulsive seizures, edema on the fundus and calcification of the basal ganglia. In young people, the presence of cataract should serve as an excuse for the exclusion of hypocalcemia. These symptoms in the presence of complaints of muscle fatigue and weakness should help in the diagnosis of hypocalcemia.

Acute hypercalcemia (hyperparathyroidism in parathyroid adenoma) can be the cause of complaints of fatigue (as well as acute psychosis or severe cerebral dysfunction).

Mental disorders

Asthenic syndrome in the picture of psychogenic disorders is recognized by characteristic concomitant manifestations: irritability, anxiety, tension headaches, dissomnic disorders, autonomic dystonia syndrome.

Depression, in addition to low mood, may manifest general weakness, fatigue, decreased motivation and motivation, sleep disorders (especially early waking up). With latent depression, complaints of weakness, fatigue, various pain syndromes, vegetative and somatic complaints dominate in the absence of objectively confirmed visceral diseases. Antidepressants cause a reverse development of somatic symptoms of latent depression.

Chronic Fatigue Syndrome

The syndrome is more common in women aged 20-40 years. Many of them have a history of a virus infection ("porcine fatigue syndrome"), more often in the form of infectious mononucleosis or Epstein-Bar's syndrome (virus). Some of these patients exhibit symptoms of latent immunological failure or a slight craniocerebral trauma in the anamnesis. For the diagnosis of chronic fatigue syndrome, fatigue and persistent or recurrent characteristic symptoms such as low fever, cervical or axillary lymphadenopathy, myalgic syndrome, headaches, migraine arthralgia, difficulty concentrating, irritability are needed for at least 6 months. , sleep disturbances. These patients often complain of muscle weakness. Neurological status - without deviations from the norm. Most of the patients show some degree of depression or neurotic disorders. The nature of the syndrome of chronic fatigue is not fully understood.

Cudogenous intermittent claudication

Manifestations of caudogenic intermittent claudication may sometimes resemble abnormal muscular fatigue in the legs.

In this disease, the patient in standing position, there is a temporary weakness in the legs. The disease is more common in old age. Weakness greatly increases with walking, sometimes to such an extent that the patient is forced to sit down, otherwise the fall will occur. The first symptom is always pain in the calves, followed by numbness in the feet, which can rise to the upper legs. Pulsation on peripheral vessels is preserved, which makes it possible to distinguish this state from the intermittent claudication of the vascular nature. In contrast to the intermittent claudication of the vascular nature, with cadogennic intermittent claudication, deep reflexes can be reduced: first only during fits of weakness, but then they decline steadily or drop out. Similarly, in the initial stages of the disease, conduction along the nerves can be slowed down during an attack, further investigation of the rates of conduction and EMG data indicate a chronic pathology of the cauda equina.

Radiography, in particular - neuroimaging of the lumbar spine, usually reveals the narrowing of the spinal canal. As a rule, the cause is a combination of pronounced degenerative pathology of the spine with arthrosis of the intervertebral joints and some protrusion of one or more intervertebral discs. One should always be careful not to extrapolate the radiographic evidence to the clinical picture: in every case, the narrowing of the spinal canal causes typical symptoms to develop. The presence of such symptoms in itself should be the basis for conducting myelography. Myelograficheskoe study should be carried out both with the lordotic distortion of the spine, and with kyphosis. The images show a violation of the passage of contrast, at least - with lordosis. The mechanism of the disease is complex: direct compression of the roots of the horse tail and impaired blood circulation in the radicular arteries.

Iatrogenic myasthenic syndrome

Increased muscle fatigue can cause drugs such as D-Penicillamine, antihypertensives, especially beta-blockers; calcium channel blockers, some antibiotics (neomycin, gentamicin, kanamycin, streptomycin, colistin, polymyxin), glucocorticoids, some analgesics, muscle relaxants, anticonvulsants; anxiolytics; antidepressants and antipsychotics. Beta-interferon in the treatment of multiple sclerosis sometimes leads to increased fatigue.

Myasthenopodobnye symptoms are sometimes observed in patients with ALS; many poisons of animal origin (venom of cobra, rattlesnake, spider "black widow", scorpion) contain neurotoxins that block neuromuscular transmission (the picture of intoxication may resemble a myasthenic crisis).

Diagnosis of pathological muscular fatigue

1. General and biochemical blood test;
2. Analysis and culture of urine;
3. Wasserman's reaction;
4. ECG (patients older than 40 years);
5. Chest x-ray and survey - abdominal cavity;
6. Electrolytes;
7. CO2;
8. 36-hour fasting (hypoglycemia);
9. Thyroid function research;
10. Daily urine for 17-ketosteroids and 17-oxycorticosteroids;
11. Daily urine for aldosterone;
12. Renin in the blood plasma;
13. Functional tests of the liver;
14. Calcium, phosphorus and alkaline phosphatase;
15. Skull and tubular bones (metastatic cancer);
16. Lymph node biopsy;
17. Gases of arterial blood;
18. CT of the abdominal cavity;
19. CT of the spine;
20. CT or MRI of the brain;
21. EMG;
22. Muscle biopsies;
23. Psychometric assessment of depression, personality traits;
24. Consultation of the therapist, endocrinologist, psychiatrist.

To confirm the diagnosis of myasthenia gravis, a proseryl test is carried out; subcutaneously injected with 2 ml of 0.05% solution of prosirin, pre-provoking weakness with muscle load, and observe the effect of injection for 40 minutes. To exclude the effect of placebo, subcutaneous injection of saline is recommended beforehand.

The study of antibodies to acetylcholine receptors and striated muscle, CT of the mediastinum (to exclude thymoma) is shown.

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