MYASTES is an autoimmune disease that causes a violation of neuromuscular transmission and is manifested by weakness and pathological fatigue of skeletal (striated) muscles. The disease is associated with the formation of antibodies against acetylcholine receptors located on the postsynaptic membrane of the neuromuscular synapse. Neonatal myasthenia gravis is a transient condition observed in infants born to mothers suffering from myasthenia and caused by the passage through the placenta of maternal antibodies to acetylcholine receptors.
Myasthenia can occur at any age, but the peak of the incidence is 20-40 and 65 - 75 years. In the overwhelming majority of cases, the disease primarily involves the eye muscles, therefore, at first, patients complain of eyelid omission and double vision. Over the next 1-2 years, most patients undergo generalization of the process with the addition of weakness of mimic and bulbar muscles, neck muscles, limbs and torso. But in some patients, the disease does not spread beyond the outer muscles of the eye (eye form). Characterized by pronounced fluctuations of symptoms during the day, in this regard, the disease is often mistaken for hysteria. The phenomenon of pathological muscle fatigue is manifested by an increase in symptoms in the background of physical exertion (for example, increased dysphagia during a meal, and dysphonia during a conversation). Characterized by the absence of autonomic disorders (disorders of innervation of the pupil or pelvic disorders), disorders of sensitivity. A neurological examination reveals a decrease in strength, which increases with the repetition of movements. To enhance ptosis, the patient is offered to fix the gaze, moving upwards or asking to raise his hands up by 30 - 60 s. To identify weakness of the muscles of the larynx, the patient is asked to count aloud up to 100. The reflexes are usually normal. Selective involvement of muscles is often noted (for example, neck flexors are weaker than extensors), this allows us to distinguish myasthenia from asthenia or hysteria. Symptoms of myasthenia can aggravate a number of drugs that can be prescribed to the patient only if absolutely necessary, provided a stable condition. This group consists of antibiotics (streptomycin, gentamicin and other aminoglycosides, polymyxin B, colthyns, tetracycline , ampicillin , erythromycin , ciprofloxacin , clindamycin), sulfanilamides, cardiovascular (beta-blockers, quinidine, lidocain , new glyphs , newest chemotherapy, cardiovascular (beta-blockers, quinidine, lidocaine , new glyphins , cardiovascular, beta-blockers, erythromycin , ciprofloxacin , clindamycin). (Trimethadione, phenytoin, carbamazepine, barbiturates), and lithium preparations chlorpromazine, diazepam (relanium) mioplegicheskie agents, quinine, corticosteroids, thyroid hormone, magnesium salts containing iodine rentgenokontra tnye substances.
In patients with generalized myasthenia, sometimes there is a rapid deterioration of the condition with the development of respiratory failure associated with weakness of the respiratory muscles or bulbar muscles (myasthenic crisis). Crisis can occur against the background of infection or taking drugs that violate neuromuscular transmission. The development of a crisis can be preceded by pronounced fluctuations of muscle weakness, a decrease in the body’s marshes, a limitation of physical activity, an increase in head downturn, increasing dysarthria, and shortness of breath . Less commonly, an increase in muscle weakness and respiratory failure is caused by an overdose of anticholinergics (cholinergic crisis). Generalized fasciculations and crumpy, hypersalivation, increased peristalsis, diarrhea, vomiting , bradycardia are in favor of this variant of the crisis.
The diagnosis . To confirm the diagnosis, a prozerin test is carried out with 2 ml of a 0.5% solution of prozerin, which is injected subcutaneously and the effect is monitored for 40 minutes. The test should be carried out only in the case when the weakness of certain muscles is detected. To eliminate the placebo effect, pre-recommended to introduce saline. To correct the possible side effects of prozerin (bradycardia, bronchospasm, arterial hypotension) you should also have a syringe with 0.5-1 mg of atropine and an Ambu bag. With the introduction of prozerin, other undesirable effects are possible - hypersalivation, lacrimation, fasciculations, diarrhea, intestinal colic , nausea , incontinence of urine and feces. The diagnosis is also confirmed by determining the content of antibodies to acetylcholine receptors. In adults with a confirmed diagnosis of myasthenia, pneumomediastinography or computed tomography of the chest is indicated to exclude thymoma. To exclude thyrotoxicosis, often combined with myasthenia, examine the content of thyroid hormones or conduct other tests that determine the functional activity of the gland. To exclude other autoimmune diseases, studies of rheumatoid factor, antinuclear antibodies are shown.
Treatment . Anticholinesterase drugs inhibit the breakdown of acetylcholine in the synapse and increase muscle strength. Often used pyridostigmine (Kalimin). When taken orally, its action begins after 10 - 30 minutes, reaches a peak after 2 hours, and then gradually decreases over 2 hours. Treatment begins with 30 mg 3 times a day, then the dose is increased to 60-120 mg every 4-6 hours. Although pyridostigmine is effective in most patients, but only a small part of them have completely regressed symptoms. Frequent side effects are abdominal pain, nausea , diarrhea, hypersalivation. The drug is contraindicated in chronic obstructive pulmonary diseases and bronchial asthma. Corticosteroids are prescribed with insufficient effectiveness of anticholinesterase drugs. They cause improvement in 70–90% of patients, but in the first 3 weeks, especially if treatment is started with a high dose, muscle weakness (including bulbar and respiratory) may increase. Upon reaching a persistent effect, proceed to a slow dose reduction. In many cases, patients are forced to take a maintenance dose of the drug for many years.
Immunosuppressants (azathioprine, less often cyclosporine and cyclophosphamide) are prescribed in case of generalized or tabloid form with poor tolerance of corticosteroids. Thymectomy is indicated in young patients (up to 60 years) with a generalized form of the disease, as well as in patients with thymomas. When signs of myasthenic crisis appear, the patient should be urgently hospitalized in the intensive care unit. It is advisable to place the patient in the half-sitting position, give oxygen through a mask or nasal catheter. Intravenously inject 1 ml of a 0.05% solution of prozerin and proceed with a slow intravenous infusion of prozerin (8–12 mg of the drug should be administered per day) If the infusion is temporarily impossible, the drug can also be administered intramuscularly at a dose of 1-2 mg). To eliminate the side effects, atropine is also administered at the same time (0.5 mg subcutaneously 3 to 5 times a day). Corticosteroids are prescribed (100 mg / day), but they may temporarily increase weakness; spend plasmapheresis. It is important to monitor the airway and lung capacity. With the development of respiratory failure conduct intubation and proceed with mechanical ventilation. When signs of infection are prescribed antibiotics (preferably cyclosporins). In cholinergic crises, anticholinesterase drugs temporarily cancel, restore the airway, pass atropine subcutaneously (0.5-1 mg every 2 hours) until dry mouth appears, cholinesterase reactants are prescribed (dipyroxime 150-100 mg intravenously or intramuscularly) if necessary, resort to intubation and mechanical ventilation.