Myasthenia gravis - Symptoms

Symptoms of myasthenia include weakness and abnormal muscle fatigability, the severity of which can fluctuate significantly throughout the day and from day to day. Weakness usually increases in the afternoon and with physical exertion and decreases after rest. Initially, the external eye muscles and eyelid muscles are often involved, causing double vision and ptosis. Symptoms are usually symmetrical. In a relatively small proportion of patients (10-15%), the disease involves only the eye muscles, but more often the symptoms gradually generalize over time. In this case, the muscles of the extremities are involved, especially their proximal parts (for example, the iliopsoas and deltoid muscles). The triceps brachii, flexors and extensors of the fingers are also involved. With weakness of the muscles of the pharynx and larynx, difficulty swallowing, attacks of suffocation, aspiration of food and respiratory secretions are possible. The main danger of the disease is associated with the weakness of the respiratory muscles, which can lead to respiratory failure and, in severe cases, to a myasthenic crisis. Deterioration can be provoked by emotional stress, infections, changes in hormonal status (especially hypothyroidism or thyrotoxicosis), various drugs such as aminoglycoside antibiotics, antiarrhythmic drugs, diuretics, magnesium salts, beta-blockers.

Transient neonatal myasthenia, characterized by impaired sucking, weak cry, and swallowing and breathing disorders, develops in 12% of newborns born to mothers with myasthenia. Symptoms of myasthenia usually appear within the first few hours after birth and can persist for several weeks to 2 months, without recurring later. There is usually no correlation between the severity of the disease in the mother and child, despite the fact that neonatal myasthenia is most likely caused by the passage of antibodies to acetylcholinesterase through the placenta. Myasthenia in children, including young children, may also be a sporadic acquired autoimmune disease similar to that which occurs in adults. At birth, in early childhood, in older children, and in adults, congenital myasthenic syndrome may also manifest itself, which is associated with genetically determined anomalies of presynaptic or postsynaptic structures that disrupt neuromuscular transmission. These conditions are usually inherited in an autosomal recessive manner. The degree of generalization of muscle weakness in various syndromes is variable: in some cases, it manifests itself only as diplopia and ptosis, while in others it is more diffuse.

Eye symptoms of myasthenia gravis

Eye symptoms occur in 90% of cases, and in 60% they are the main ones. They are characterized by the following manifestations.

• Ptosis develops gradually, bilaterally and often asymmetrically.
• More pronounced at the end of the day, least of all upon awakening.
• It gets worse after looking up for a long time due to fatigue.
• If one eyelid is lifted by hand while the patient is looking up, small oscillatory movements of the paired eyelid will appear.
• Cogan's sign is an upward twitching of the eyelid after lowering the gaze from above to the primary position.
• Positive ice test: ptosis is reduced after applying ice to the eyelid for 2 minutes. The test is negative in non-myasthenic ptosis.

Diplopia is often vertical but may involve any or all extraocular muscles. Pseudointernuclear ophthalmoplegia may occur. The patient with stable deviation may benefit from muscle surgery, injection of CI botulinum toxin, or a combination of both.

Nystagmoid movements may be observed in extreme gaze abduction.

Edrophonium test

Edrophonium is a short-acting anticholinesterase agent that increases the amount of acetylcholine in the neuromuscular junction. In myasthenia, this results in a transient reduction in symptoms such as weakness, ptosis, and diplopia. The sensitivity of the test is 85% for ocular myasthenia and 95% for systemic myasthenia. Potential but rare complications include bradycardia, loss of consciousness, and death is also possible, so the test should not be performed without an assistant, and the resuscitation gurney should be at hand in case of sudden cardiorespiratory complications. The test is performed as follows:

The initial level of ptosis or diplopia is objectively assessed using the Hess test.

1. Atropine 0.3 mg is administered intravenously, which minimizes muscarinic side effects.
2. 0.2 ml (2 mg) of edrophonium hydrochloride is administered intravenously. If symptoms subside, the test is stopped immediately.
3. If there is no hypersensitivity, the remaining 0.8 ml (8 mg) is administered after 60 seconds.
4. A final measurement and/or repetition of the Hess test is carried out and the results are compared, remembering that the action lasts only 5 min (Fig. 18.1121.

[ 1 ], [ 2 ], [ 3 ], [ 4 ]