[Yao's Anesthesia] Anesthesia management of myasthenia gravis (1)

A patient with myasthenia gravis, female, 25 years old, G3P2, 24 weeks of gestation, intrauterine death, planned to undergo cervical dilation and uterine evacuation, has progressively worsening diplopia and dysphagia symptoms
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Suffering from myasthenia gravis (MG) for 10 years, she underwent thymectomy for thymoma in the early stage of her second pregnancy 2 years ago, and the symptoms disappeared after surgery, and she stopped taking medicine
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The vital signs were as follows: pulse 60 beats/min, blood pressure 150/80 mmHg, respiratory rate 20 beats/min
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Arterial oxygen saturation was 98% on inhalation
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Height 155cm, weight 65kg
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A.
Diseases and Differential Diagnosis 1.
What is the clinical course of myasthenia gravis (MG)? 2.
What is the cause of myasthenia gravis and how is it diagnosed? 3.
What diseases should be considered in the differential diagnosis of this patient? 4.
What is the difference between myasthenia gravis (MG) and Lambert-Eaton myasthenic syndrome? 5.
Briefly describe the clinical classification of myasthenia gravis
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6.
What are the treatment measures for patients with myasthenia gravis? 7.
What is the role of surgery in the treatment of myasthenia gravis? 8.
How does pregnancy affect the course of myasthenia gravis? B.
Preoperative assessment and preparation 1.
How to conduct preoperative assessment for such patients? 2.
What laboratory tests are required before surgery? 3.
How to choose preoperative medication for such patients? A.
What is the clinical course of disease and diagnosis 01 Myasthenia gravis (MG)? MG is characterized by fluctuating muscle weakness that worsens with activity and relieves with rest
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MG often develops insidiously over months to years
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The first symptoms are usually ocular symptoms, including ptosis and diplopia
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Extraocular muscle involvement can range from single ophthalmoplegia to complete ophthalmoplegia
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Muscle fatigue can cause nystagmus
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The pupillary sphincter is generally not involved
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80% to 85% of MG patients often progress from ocular symptoms to generalized muscle weakness
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The prognosis is good if symptoms are confined to the eye for more than 2 years
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Dysphonia, dysphagia, and difficulty chewing occur after bulbar muscle involvement
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Decreased oral feeding and nasal reflux may cause weight loss, and a nasal sound suggests soft palate laxity
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Involvement of the facial muscles, especially the levator muscles at the corners of the mouth (levator lip and levator angiitis) produces the characteristic "snarling" face of myasthenia
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Weakness of the limbs is only seen in 15% to 20% of patients with muscle weakness
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Proximal muscles are more frequently involved than distal muscles
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Occasionally, the neck extensors (rectus posterior major, minor rectus posterior minor) may be weak so that the patient cannot keep the head up
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Respiratory muscle weakness manifests as dyspnea, especially in the supine position
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If the diaphragm is involved, there is a weak cough and inability to vocalize
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MG symptoms can be exacerbated by a number of factors, including physical and mental stress, infection, intense sunlight exposure (especially when ocular signs are the predominant symptom), hyperthyroidism, or elevated body temperature during infection
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Medications such as quinidine, procainamide, aminoglycosides, penicillin, and calcium channel blockers can also make symptoms worse
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The use of the aforementioned antibiotics in the treatment of infection can worsen respiratory distress and require mechanical ventilation in severe cases
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 What is the cause of myasthenia gravis and how is it diagnosed? MG is an autoimmune disease caused by the attack of nicotinic acetylcholine receptors (AchR) on the motor endplate by autoantibodies and T cells
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Antibodies are detectable in 80% of patients with generalized myasthenia and in 50% of patients with only ocular symptoms
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The initial diagnosis of MG is usually based on the history and clinical examination, which can then be confirmed by a series of diagnostic tests
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Clinical tests of stress tolerance include upward gaze time, hand abduction time, and spirometry
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Other tests to confirm MG include the following: • Electrophysiological tests • Pharmacological tests • Serological tests 03 What diseases should be considered in the differential diagnosis of this patient? Although the diagnosis in this patient was consistent with myasthenia gravis (MG), careful differentiation should be made considering that some disorders are very similar to MG
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Both botulism and Lambert-Eaton myasthenic syndrome (LES) can cause muscle weakness and ophthalmoplegia
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Botulism can be distinguished from MG by the early involvement of cranial nerves, enhanced pupillary light reflexes and increased muscle responses after repeated nerve stimulation
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LES causes distal muscle weakness, but muscle weakness improves with activity, and 50% are associated with pulmonary oat cell tumors, which can also be associated with an autonomic deficit characterized by dry mouth, orthostatic hypotension, and urinary retention
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Hyperthyroidism can also manifest as general weakness, but at the same time with abnormal thyroid function
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Patients with neurasthenia can also complain of muscle weakness, but it is characterized by the disappearance of the weakness when each muscle group is tested independently
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In addition, progressive external ophthalmoplegia, restrictive cardiomyopathy, muscular dystrophy, brain tumor, amyotrophic (spinal) lateral sclerosis, neostigmine-sensitive polymyasthenia, and dextromethamine, Drugs such as dextrocuronine, aminoglycoside antibiotics, quinine, procainamide, and calcium channel blockers can all cause myasthenia-like symptoms
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 04What is the difference between myasthenia gravis (MG) and Lambert-Eaton myasthenic syndrome? 05 Briefly describe the clinical grading of myasthenia gravis
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The Osserman and Genkins clinical grades according to symptomatology are as follows: Grade 1: ocular symptoms only Grade 1A: ocular symptoms with EMG manifestations of peripheral muscle involvement Grade 2A: mild systemic symptoms Grade 2B: more severe and Rapidly progressive symptoms Grade 3: acute with severe bulbar symptoms occurring within weeks to months Grade 4: advanced disease with severe bulbar symptoms and generalized weakness 06 What are the treatment options for patients with myasthenia gravis? MG can take a variety of different treatment measures, generally divided into: • Drug therapy • Surgery • Plasma exchange By inhibiting the enzymatic hydrolysis of Ach, anticholinesterase drugs prolong the effect of Ach in the neuromuscular junction postsynaptic membrane
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The most common side effects of anticholinesterase drugs are due to the muscarinic effects of Ach and include bradycardia, gastrointestinal colic, bronchospasm, and increased oral and respiratory secretions
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Overdose of anticholinesterase drugs can cause cholinergic crisis, manifested as severe muscle weakness, the mechanism of which is the persistent depolarization of muscle fibers caused by excessive Ach at the neuromuscular junction
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Myasthenic symptoms of cholinergic crisis may be mistreated with anticholinesterases as myasthenia gravis, leading to a vicious circle of exacerbation of cholinergic crisis
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When clinically distinguishing the two, pupil size may provide clues to the etiology of muscle weakness
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Sympathetic activation and pupil dilation in patients with myasthenia gravis due to hypercapnia
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In cholinergic crisis, Ach causes mydriasis
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It should be noted that patients with ocular signs as the predominant symptom respond poorly to cholinesterase inhibitors
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Pyridostigmine bromide (masteryrone), a commonly used drug for the treatment of myasthenia gravis, causes less muscarinic side effects
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Ephenidium chloride (Tengxilong) 5 to 10 mg IV is usually given between two conventional anticholinesterase medications to determine whether the patient is overdose or underdose
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Glucocorticoids are used in addition to, not as a substitute for, anticholinesterase therapy
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Appropriate prednisone treatment can completely relieve symptoms in 70% to 80% of patients within weeks to months
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Glucocorticoids have inhibitory effects on multiple aspects of the immune system, reducing acetylcholine receptor (AchR) antibodies and eliminating the anti-AchR activity of peripheral blood lymphocytes
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Common side effects of high-dose glucocorticoid therapy include systemic immunosuppression, infection, cataracts, myopathy, osteoporosis, diabetes, and peptic ulcers
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Most patients require 40 to 60 mg of prednisone daily
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Adrenocorticotropic hormone (ACTH) is used for the treatment of patients with severe MG, often after failure of glucocorticoid therapy
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However, ACTH therapy was gradually replaced by plasma exchange
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Plasma exchange has been shown to be effective in removing circulating antibodies and can be used to stabilize the condition of patients with myasthenic crisis or to preoperatively treat patients with severe myasthenic symptoms
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After treatment, the patient's condition improved rapidly, but the effect was short-lived
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Plasma exchange combined with intravenous infusion of concentrated immunoglobulin 400mg/(kg·d), once every other day, 5 times in a row, can rapidly improve the condition, and the effect lasts for several weeks
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 07What role does surgery play in the treatment of myasthenia gravis? Although efficacy data for thymectomy are derived from retrospective analyses, it has been widely used for the treatment of myasthenia gravis, especially myasthenia gravis with thymoma and earlier systemic symptoms
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The purpose of thymectomy as a treatment for MG is to relieve symptoms, thereby reducing the dose of immunosuppressants
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Thymoma is seen in 15% of MG patients, and thymic hyperplasia is seen in 80% of MG patients
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The improvement of clinical symptoms after thymectomy provides further evidence for the connection between the thymus and MG, therefore, thymectomy may be a reasonable choice for most patients with MG
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However, thymectomy should not be performed in prepubertal children and in patients with MG whose main symptoms are ocular signs
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In addition, if the patient's symptoms can be relieved by drug treatment, the patient is not suitable for thymectomy
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The surgical approach of MG thymectomy includes transsternal or transcervical approach
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The transsternal approach has better surgical exposure and more complete resection
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The main advantage of the transcervical approach is that it is less invasive and has a mortality rate of about 0%, compared to about 9% for the transsternal approach
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The postoperative mechanical ventilation rate was 10% for the transcervical approach and 50% for the transsternal approach
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 A8.
How does pregnancy affect the course of myasthenia gravis? The course of MG during pregnancy is unpredictable, and optimal control of MG in early pregnancy does not mean that symptoms will worsen or resolve with pregnancy
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Symptoms worsen in 1/3 of pregnant women, which can occur at any stage of pregnancy, but are more common in the first three months of pregnancy or one month after delivery
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Myasthenia symptoms can improve in 20% to 40% of pregnant women in the second and third trimesters
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Postpartum complications such as infection appear to increase the risk of worsening MG symptoms
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MG maternal mortality was negatively correlated with the duration of MG, with the highest mortality in the first year of MG onset and the lowest 7 years after MG onset
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B.
Preoperative evaluation and preparation 01How to conduct preoperative evaluation for such patients? The preoperative visit should identify factors that may predict postoperative mechanical ventilation, including the course and severity of MG and the total daily dose of pyridostigmine or other drugs
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This information can guide anesthesiologists in planning anesthesia, choosing preoperative medication, and rationally arranging postoperative monitoring
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Whether to adjust a patient's anticholinesterase medication remains highly controversial
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In mild patients, discontinuation of anticholinesterase drugs seems more appropriate, since discontinuation of the drug may predispose the patient to vagal arrhythmias during anesthesia
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In addition, anticholinesterase drugs inhibit plasma cholinesterase and acetylcholinesterase, so the metabolism of ester local anesthetics, succinylcholine, and mevidone may be slowed
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Of course, patients who cannot be discontinued should continue anticholinesterase therapy, but the anesthesiologist should be aware that postoperative anticholinesterase requirements may be significantly reduced
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It should be determined whether the patient is taking or has taken glucocorticoids in the past year
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Because the incidence of other autoimmune diseases in patients with myasthenia is higher, and these diseases may have their own anesthetic characteristics, we should be alert to the occurrence of hypothyroidism, pernicious anemia, systemic lupus erythematosus and rheumatoid arthritis
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 02What laboratory tests are required before surgery? The determination of which laboratory tests are required should be based on the patient's medical history
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Electrolyte abnormalities, especially hypokalemia, which often exacerbate muscle weakness, should be ruled out in addition to routine preoperative laboratory tests
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Because most patients with this disease are taking glucocorticoids, blood glucose levels should be checked
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Care should be taken to measure cyclosporine blood levels in order to adjust the dose and prevent its concentration from exceeding toxic levels
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Blood counts and liver and kidney function should be checked
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If the patient needs to be operated under general anesthesia, preoperative blood gas analysis and pulmonary function test can be used as a reference basis for postoperative extubation, especially for patients requiring mechanical ventilation after surgery
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Generally speaking, in patients with thymoma, the tumor is located in the anterior mediastinum, and attention should be paid to the degree of compression and advancement of the trachea, because this may cause difficulty in tracheal intubation
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Intrathoracic airway or vascular obstruction may occur in patients with myasthenia during induction of anesthesia, and preoperative respiratory flow-volume loops can distinguish intrathoracic or extrathoracic obstruction
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 03How to choose preoperative medication for such patients? The preoperative visit should include an explanation to the patient about the anesthesia process and the possibility of postoperative mechanical ventilation, which usually helps to reduce anxiety and reduce the amount of preoperative sedation
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Try to avoid drugs that depress your breathing
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Glycopyrrolate can be used to reduce increased secretions caused by cholinesterase inhibitors
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Patients taking glucocorticoids before surgery should be given a stress dose of glucocorticoids during the perioperative period
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Notes/Chen Lingjun Typesetting/Dingdang Maruko Ma and listen to the next decompositionEND