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Myasthenia gravis
Last reviewed: 23.04.2024
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Myasthenia gravis is an autoimmune disease, manifested by episodes of muscle weakness and fatigue, which is based on the destruction of acetylcholine receptors by factors of humoral and cellular immunity. More often affects young women and older men, although it can occur at any age. Myasthenia gravis symptoms are aggravated when the muscles are stressed and decrease at rest. It is diagnosed by intravenous administration of eudrophonia, which for a short time reduces weakness. Treatment of myasthenia includes anticholinesterase drugs, immunosuppressants, glucocorticoids, thymectomy and plasmapheresis.
Myasthenia gravis is an acquired autoimmune disease, manifested by weakness and pathological fatigue of skeletal muscles. Myasthenia gravis incidence is less than 1 case per 100 000 population per year, and the prevalence is from 10 to 15 cases per 100 000 population. Myasthenia gravis is especially common in young women and men over 50 years of age.
[Causes of myasthenia gravis
Myasthenia gravis develops as a result of an autoimmune attack on postsynaptic acetylcholine receptors, which violates neuromuscular transmission. What triggers the formation of autoantibodies is unknown, but the disease is associated with the pathology of thymus, thyrotoxicosis and other autoimmune disorders. The role of the thymus in the development of the disease is not clear, but in 65% of cases of myasthenia gravis the thymus is hyperplastic, and in 10% there is thymoma. Among predisposing factors - infections, surgery and some medications (for example, aminoglycosides, quinine, magnesium sulfate, procainamide, calcium channel blockers).
Rare forms of myasthenia gravis. With the eye form, only the external muscles of the eye suffer. Congenital myasthenia gravis is a rare disease with an autosomal recessive type of inheritance. This is, rather, the result of structural disorders of the postsynaptic receptor, rather than a consequence of the autoimmune process. Oftenmooplegia is common.
12% of children whose mothers suffer from myasthenia gravis are born with neonatal myasthenia gravis. This is due to the passive penetration of IgG antibodies across the placenta. The general muscle weakness passes in some days - weeks, in parallel to decrease in a titer of antibodies in a blood of the child.
Symptoms of myasthenia gravis
The most common symptoms of myasthenia gravis: ptosis, diplopia and muscle weakness after exercise. Weakness passes after rest, but with repeated exercise it recurs. In 40% of cases, the eye muscles are initially affected, later the prevalence of this lesion reaches 85%. In the first 3 years, in most cases, the process is generalized. Often there is weakness in the proximal parts of the limbs. Sometimes patients complain about tabloid disorders (eg, voice changes, nasal regurgitation, asphyxia, dysphagia). In this case, sensitivity and deep tendon reflexes do not change. The severity of violations varies with a period of several hours - days.
Myasthenic crisis - severe generalized tetraparesis or life-threatening weakness of the respiratory muscles, develops in about 10% of cases. It is often associated with an infection that activates the immune system. After the onset of respiratory failure, respiratory arrest may occur very quickly.
Diagnosis of myasthenia gravis
Diagnosis is based on complaints, clinical picture and special research data. To assess the defeat, the patient is asked to stretch the muscle to fatigue (for example, keep the eyes open until ptosis develops, or loudly count until speech is broken); then intravenously injected 2 mg of edrophonia - an anticholinesterase preparation with a short-term action (<5 min). If there are no adverse reactions within 30 s (eg, bradycardia, atrioventricular block), another 8 mg is given. The criterion of positivity of the sample: rapid (<2 min) restoration of muscle function. In most cases, myasthenia gravis is positive, as in many other neuromuscular diseases. Conducting the sample may cause increased weakness due to the cholinergic crisis (see below). During the test, you need to have a resuscitation kit and atropine (as an antidote) on hand.
Even with a clearly positive anticholinesterase assay, the level of antibodies to acetylcholine receptors in serum should be determined to confirm the diagnosis and to conduct EMG. Antibodies are detected in 90% of cases of generalized myasthenia gravis and only in 50% of cases of the eye form. The level of antibodies does not correlate with the severity of the disease.
Irritation by a burst of pulses (2-3 per 1 second) on EMG in 60% of cases of myasthenia gravis reveals a significant decrease in amplitude in the sequence of action potentials.
After the diagnosis of myasthenia gravis, CT or MRI of the thoracic organs is performed for the purpose of finding thymoma. Carry out screening tests to identify autoimmune diseases often accompany gravis (e.g., deficiency of vitamin B 12, thyrotoxicosis, rheumatoid arthritis, systemic lupus erythematosus). Testing lung function (eg, forced vital capacity of the lungs) helps assess the threat of respiratory arrest. With a myasthenic crisis, it is necessary to identify the source of infection.
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Treatment of myasthenia gravis
Patients with respiratory arrest require intubation and mechanical ventilation. Anticholinesterase drugs and plasmapheresis alleviate complaints, and glucocorticoids, immunosuppressants and thymectomy reduce the severity of the autoimmune reaction. With congenital myasthenia gravis, anticholinesterase drugs and immunomodulatory treatment are ineffective and should not be used.
Symptomatic treatment of myasthenia gravis
The basis of symptomatic treatment - anticholinesterase drugs - does not affect the cause of the disease, rarely relieve all complaints, and myasthenia gravis can become refractory to their use. Pyridostigmine begins with 30-60 mg orally after 3 to 4 hours and, with tolerability, is brought to a maximum dose of 180 mg 6-8 times / day. In severe dysphagia, especially in the mornings, it is possible to take long-acting capsules for 180 mg at night, but their effect is weaker. If parenteral administration is necessary (for example, because of dysphagia), neostigmine can be used (1 mg corresponds to 60 mg of pyridostigmine). Anticholinesterase drugs can cause abdominal cramps and diarrhea. In such cases, appoint atropine 0.4-0.6 mg orally or propantheline 15 mg 3-4 times / day.
The cholinergic crisis is a muscle weakness caused by an overdose of neostigmine or pyridostigmine. A mild crisis can hardly be distinguished from a spontaneous deterioration in the state of myasthenia gravis. But severe cholinergic crisis is characterized by excessive lacrimation, hypersalivation, tachycardia and diarrhea, and for myasthenia - no. With worsening of patients who respond well to treatment, some doctors perform an ectrophonia test because it is positive only with the myasthenic crisis, and when cholinergic it is not. Others recommend simply providing respiratory support and interrupting the use of anticholinesterase drugs for several days.
Immunomodulatory treatment of myasthenia gravis
Immunosuppressants suppress the autoimmune reaction and slow the course of the disease, but they do not give a quick reduction of complaints. When intravenous immunoglobulin 400 mg / kg 1 time / day 5 days in 70% of cases, improvement occurs after 1-2 weeks.
Supportive therapy usually requires glucocorticoids, but with the myasthenic crisis they do not have immediate effect, and after a high dose of glucocorticoids in more than half of the cases, a sharp deterioration occurs. Therefore, start with 20 mg 1 time / day, every 2-3 days the dose is increased by 5 mg up to 60-70 mg and go to 1 reception every other day. Improvement occurs in a few months; then the dose is reduced to the required minimum.
Azathioprine 2.5-3.5 mg / kg 1 time / day can be as effective as glucocorticoids, although it may not manifest itself for many months. By taking cyclosporine 2-2.5 mg / kg orally 2 times / day, you can reduce the dose of glucocorticoids. These drugs require special care. Methotrexate, cyclophosphamide and mycophenolate mofetil may be effective.
Thymectomy is acceptable for most patients younger than 60 years with generalized myasthenia gravis. The operation should be performed in all cases of thymoma. Subsequently, in 80% of cases a remission occurs or it is possible to reduce the amount of maintenance therapy.
During the myasthenic crisis and before thymectomy, in patients refractory to therapy, plasmapheresis can be effective.
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