myasthenia gravis
Introduction
Introduction Myasthenia gravis is an autoimmune disease that primarily affects the acetylcholine receptor (AchR) on the postsynaptic membrane of neuromuscular junctions. Clinical manifestations are partial or systemic skeletal muscle weakness and fatigue, increased symptoms after activity, and reduced symptoms after rest and treatment with cholinesterase inhibitors (ChEI). The incidence rate is 8-20/100,000, and the prevalence rate is 50/100,000. The incidence rate in southern China is higher. Patients with myasthenia gravis often have other autoimmune diseases such as hyperthyroidism, thyroiditis, systemic lupus erythematosus, rheumatoid arthritis, and pemphigus. It is usually relieved in the morning, the symptoms are aggravated after repeated activities, and there is a degree of remission after rest. Therefore, the trend of "morning light and heavy" is the main clinical feature of this disease.
Cause
Cause
The causes of myasthenia gravis are divided into two categories, one is congenital hereditary, rare, and has nothing to do with autoimmunity. The second category is autoimmune diseases, the most common. The cause of the disease is still unclear and is generally considered to be related to infection, drugs, and environmental factors. At the same time, 65% to 80% of patients with myasthenia gravis have thymic hyperplasia, and 10% to 20% have thymoma.
Examine
an examination
Related inspection
Troponin EMG muscle tone examination
1. Newcastle test
Adults generally use neostigmine 1 ~ 1.5mg intramuscular injection, if the symptoms improve after 10 to 15 minutes after injection, peaked 30 to 60 minutes, lasting 2-3 hours, that is, the neostigmine test is positive.
2. Thymus CT and MRI
Thymic hyperplasia or thymoma can be found and should be further clarified if necessary.
3. Repeat electrical stimulation
Repetitive nerve electrical stimulation is a commonly used examination method with definite diagnostic value. The motor is used to stimulate the motor nerve, and the amplitude of the reflected potential of the muscle is recorded. If the muscle potential of the patient gradually declines, it indicates the possibility of lesion at the neuromuscular junction.
4. Single fiber EMG
Single fiber EMG is a more sensitive means of detecting abnormalities in neuromuscular junctions than repetitive nerve electrical stimulation. Neuromuscular conduction abnormalities can be found based on an increase in "trembling" when repetitive nerve electrical stimulation and clinical symptoms are normal, and sensitivity is highest in all muscle weakness tests.
5. Detection of acetylcholine receptor antibody titer
The detection of acetylcholine receptor antibody titers is characteristic for the diagnosis of myasthenia gravis. Serum acetylcholine receptor antibodies can be detected in 80% to 90% of systemic type and 60% of myocardium myasthenia gravis. The level of antibody titer is not exactly the same as the severity of clinical symptoms.
Diagnosis
Differential diagnosis
1, with oropharynx, limb muscle weakness: such as muscular dystrophy, amyotrophic lateral sclerosis, neuropathy or hyperthyroidism caused by muscle weakness, other causes of ophthalmoplegia. Ocular eye spasm is occasionally accompanied by mild eye muscle weakness, but its eyelid closure is weak and involves upper and lower eyelids. These diseases are not difficult to identify with MG based on medical history, neurological examination, electrophysiological examination, and neostigmine test.
2, Lambert-Eaton syndrome: most of the onset after 50 years old, more common in men. More associated with tumors, the most common in small cell lung cancer. Mainly the weakness of the trunk muscles at the proximal extremities, the lower extremity symptoms are heavier than the upper limbs, weight loss and fatigue, and the action is slow. Muscles feel tired after the activity, but if the contraction continues, the muscle strength can be temporarily improved. Occasionally, the extraocular muscles and the medulla oblongata muscles are involved. About 1/2 cases have abnormal limbs, dry mouth, impotence, and caustic soda. Esterase inhibitors are ineffective for treatment. The tendon reflex is weak but there is no muscle atrophy. And myasthenia gravis is more common in women under 40 years old. Often accompanied by thymic tumors, the whole body muscles can be affected, with the most active muscle involvement. Myasthenia is weak in the morning, heavy in the afternoon, increased after the activity, and reduced or disappeared after the break. Radon reflexes are usually unaffected and cholinesterase inhibitors are effective.
3, drug poisoning: botulinum toxin poisoning, organophosphorus pesticide poisoning, snake bite caused by neuromuscular transmission disorders, with neostigmine or phenolic ammonium after clinical symptoms will also improve, but these diseases are clear Medical history. Among them, botulinum poisoning has an epidemic history, and its toxin acts on the presynaptic membrane, affecting the transmission function of the nerve-muscle junction, and skeletal muscle spasm should be treated in time for intravenous guanidine hydrochloride and intravenous glucose and saline.
