• It is a disease caused by immune-mediated neuromuscular blockade. It is sporadic. Antibodies against the acetylcholine (Ach) receptor protein have developed in the motor plaque. It is more common in young adult women (20-30 years old).
• As a result of the involvement of respiratory muscles, they die from respiratory failure. The disease can manifest itself at various ages.
Neonatal myasthenia
• It occurs as a result of transplacental transmission of antibodies from the mother with myasthenia gravis to the fetus. Symptoms begin in the first hours of life. There are signs such as weakness in sucking, generalized weakness, inability to get the Moro reflex, ptosis, respiratory failure. It resolves in 1-4 weeks after the antibodies are cleared from the blood.
Congenital myasthenia
• In this form, anti-acetylcholine receptor antibodies cannot be demonstrated in the patient's serum. Weakness is seen mainly in the extraocular and facial muscles.
Two-year-old ptosis is usually the first symptom. Breathing difficulties and trunk muscle weakness follow. The disease continues throughout life.
Juvenile myasthenia
• This type is similar to the adult type. It differs only in that it occurs at the end of the first decade of life or in the second decade of life.
• The disease may occur as presynaptic (choline acetyltransferase defect, Lambert-Eaton myastanic syndrome-like disease), synaptic (acetylcholine esterase defect) and postsynaptic (primary acetylcholine receptor defect, slow-rate and sodium channel defects, Dok7 mutation). Administration of acetylcholine esterase inhibitor in acetylcholine esterase defect, slow channel defect and Dok7 mutation worsens the disease.
• The most common type is Primary AChR deficiency in the postsynaptic group.
Clinical Findings
• Ptosis and extraocular muscle weakness are the earliest and most prominent findings in myasthenia gravis. Patients get tired early. They complain that the strength gradually decreases with repetitive movements. Later in the day, ptosis occurs.
There is a "myopathic expression" on the face due to the faint nasolabial grooves and low corner of the mouth. Diplopia, dysphagia and dysarthria are frequently observed. In advanced cases, patients support their jaws with their hands to speak. Weakness is greater in the proximal muscles. Therefore, they have more difficulty in movements such as climbing stairs, getting up from a chair, raising their hands in the air.
• While there are only ocular findings in prepubertal patients, the incidence of generalized symptoms increases in postpubertal patients.
• Diseases accompanying myasthenia gravis: Rheumatoid arthritis, thyroiditis, thymoma and diabetes mellitus.
Diagnosis
• Electromyography (EMG) is more specific diagnostic than muscle biopsy in myasthenia gravis. Decreased response to repetitive nerve stimulation is seen. The amplitude of the muscle potentials decreases rapidly and the muscles become more resistant to stimulus. Motor nerve conduction velocity remains normal. This specific EMG pattern corresponds to clinical fatigue and is rapidly reversed by administration of a cholinesterase inhibitor.
• A clinical test for myasthenia gravis is the administration of a short-acting cholinesterase inhibitor, usually IV edrophonium chloride. When 2-10 mg of edrophonium chloride is given, ptosis and ophthalmoplegia are resolved within a few seconds and fatigue in other muscles is reduced. Edrophonium is not recommended for use in infants <2 years of age. In patients younger than 2 years of age, the test is performed by intramuscular administration of prostigmine methylsulfate (neostigmine). Because of the ventricular fibrillation effect of prostigmine, IV administration is not recommended.
• Anti-Ach antibodies can be seen in plasma, but are not always shown. Serum creatine kinase (CK) levels are normal in myasthenia gravis. There is no cardiac involvement, ECG findings are normal.
Treatment
• Pridostigmine and neostigmine
• corticosteroid
• Intravenous immunoglobulin (IVIG)
• Some patients have benefited from plasmapheresis and thymectomy.
• Thymectomy is most effective in those with high titers of anti-Ach receptor antibodies in the serum and those with a duration of symptoms <2 years. It is ineffective in those with congenital or familial myasthenia gravis.
• Thymectomy indications
- In cases that do not respond to the drug and in cases where the side effects of the drug cannot be controlled with atropine,
- If the patient is too weak to perform daily activities,
- If the patient shows bulbar or respiratory symptoms, steroid therapy or thymectomy is performed.
• Untreated, myasthenia gravis is usually progressive and can be life-threatening due to respiratory muscle involvement and risk of aspiration. Children with myasthenia gravis cannot tolerate neuromuscular blocking drugs such as succinylcholine and pancuronium and may become paralyzed for weeks after a single dose. Also, some antibiotics can increase myasthenia (gentamicin and other aminoglycosides).
This is a table showing the medications that should be avoided for patients with myasthenia gravis
