What's going on
At the point of contact between nerve and muscle, the nerve impulse is transmitted using acetylcholine, which binds to receptors on the muscle. In myasthenia gravis, the immune system produces antibodies that block and destroy these receptors. The signal gets worse and worse as contractions are repeated - hence the weakness that increases with exercise.
A significant proportion of patients exhibit changes in the thymus gland (thymus): its hyperplasia or tumor - thymoma. Therefore, a chest CT scan is included in the mandatory examination.
Symptoms
- Drooping of the upper eyelid (ptosis), often asymmetrical, worsening in the evening and when looking up
- Double vision that comes and goes
- Weakness of facial muscles: “smile with a roar”, inability to puff out the cheeks
- Difficulty chewing - chewing muscles get tired while eating
- Difficulty swallowing, choking, fluid getting into the nose
- Nasal, “fading” voice: towards the end of the conversation, speech becomes unintelligible
- Weakness in the arms and legs, mainly in the proximal parts: difficulty combing one's hair, difficulty climbing stairs
Diagnostics
- Осмотр невролога с нагрузочными пробами: длительный взгляд вверх, повторные приседания, счёт вслух.
- Анализ крови на антитела к ацетилхолиновым рецепторам, при отрицательном результате — к MuSK.
- ЭНМГ с ритмической стимуляцией: характерное снижение амплитуды ответа при повторной стимуляции.
- КТ или МРТ органов грудной клетки для оценки вилочковой железы.
- Обследование щитовидной железы — аутоиммунные заболевания часто сочетаются.
Treatment
- Anticholinesterase drugs - increase the amount of acetylcholine in the synapse, provide rapid symptomatic improvement
- Glucocorticosteroids and other immunosuppressants - act on the cause, are selected over a long period of time
- Thymectomy - removal of the thymus gland; mandatory for thymoma and is considered in some patients without it
- Plasmapheresis and intravenous immunoglobulins - during exacerbations and crises
- Regime: dosing loads, resting during the day, avoiding overheating and infections
Medicines to avoid
In myasthenia gravis, a number of common medications impair neuromuscular transmission. The list should be known and shown to any doctor, including a dentist and surgeon.
- Some antibiotics: aminoglycosides, fluoroquinolones, macrolides in high doses
- Magnesium sulfate - including during pregnancy
- Beta blockers, a number of antiarrhythmic drugs
- Muscle relaxants used during anesthesia - the anesthesiologist must be warned
- Some psychiatric drugs and high-dose statins
Practical advice: carry a card or note in your phone with your diagnosis, medications taken and a list of contraindications. This speeds up assistance in an emergency.