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Myasthenia gravis

Definition
MG is an autoimmune disorder characterized by fatigable muscle weakness which results from antibodies targeting the postsynaptic neuromuscular membrane.
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Pathophysiology
MG is caused by autoantibodies directed mainly against AChRs, muscle-specific kinase, and lipoprotein receptor-related peptide.
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Epidemiology
The incidence and prevalence rate of MG is estimated at 0.53 cases per 100,000 person-years and 7.8 persons per 100,000 population, respectively.
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Disease course
Antibodies belonging to IgG1 and IgG3 subclass direct antibodies mainly against AChRs, which disrupt neuromuscular transmission causing ocular, oropharyngeal, limb, axial, and respiratory muscle weakness. Thymoma and myasthenia crisis may even cause death.
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Prognosis and risk of recurrence
Mortality associated with MG is about 5-14%.
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Key sources
The following summarized guidelines for the evaluation and management of myasthenia gravis are prepared by our editorial team based on guidelines from the American College of Chest Physicians (ACCP 2023), the American Academy of Neurology (AAN 2020; 2011), the Myasthenia Gravis Foundation of America (MGFA 2016), the Society of Critical Care Medicine (SCCM 2016), the European Society of Medical Oncology (ESMO 2015), and the European Federation of Neurological Societies (EFNS 2014; 2010).
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Guidelines

1.Diagnostic investigations

Clinical assessment: obtain clinical evaluation by physicians skilled in the evaluation of neuromuscular disease.
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  • Respiratory evaluation

2.Respiratory support

Airway clearance: consider offering glossopharyngeal breathing for lung volume recruitment and airway clearance in patients with hypoventilation.
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  • Noninvasive ventilation

  • Invasive ventilation

3.Medical management

Setting of care: admit patients with impending crisis to hospital and obtain close observation of respiratory and bulbar function, with the ability to transfer to an ICU if it progresses to manifest crisis.
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  • Acetylcholinesterase inhibitors

  • Corticosteroids

  • Immunosuppressants

  • Rituximab

  • IVIG

  • Amifampridine

4.Nonpharmacologic interventions

Physical training: consider offering physical training in patients with mild MG as it is safe and produces some improvement in muscle force.
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5.Therapeutic procedures

Plasma exchange: as per MGFA 2016 guidelines, perform plasma exchange as short-term treatment option in patients with MG in the following circumstances:
life-threatening signs such as respiratory insufficiency or dysphagia
preparation for surgery in patients with significant bulbar dysfunction
a rapid response to treatment is needed
other treatments are insufficiently effective
before initiating corticosteroids if deemed necessary to prevent or minimize exacerbations.
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  • Palliative radiotherapy

6.Perioperative care

Neuromuscular blockade
Administer a reduced dose (based on peripheral nerve stimulation with train-of-four monitoring) of a neuromuscular blocking agent in patients with MG.
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Insufficient evidence to recommend monitoring a specific muscle group in patients with MG undergoing treatment with neuromuscular blocking agents.
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7.Surgical interventions

Thymectomy: as per MGFA 2016 guidelines, perform thymectomy as an option to potentially avoid or minimize the dose or duration of immunotherapy in patients with non-thymomatous MG, or if patients fail to respond to an initial trial of immunotherapy or have intolerable side effects from that therapy. Recognize that thymectomy for MG is an elective procedure because of the long delay in onset of effect. Perform thymectomy when the patient is stable and deemed safe to undergo a procedure where postoperative pain and mechanical factors can limit respiratory function.
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8.Specific circumstances

Pediatric patients: recognize that pediatric patients with acquired autoimmune ocular MG are more likely than adult patients to go into spontaneous remission. Consider administering pyridostigmine as initial therapy in young pediatric patients with only ocular symptoms of MG. Consider initiating immunotherapy if goals of therapy are notMET .
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  • Pregnant patients

  • Patients with ocular myasthenia

9.Patient education

General counseling: educate patients with clinical MG or even isolated positive anti-AChR antibodies about the risks of myasthenic crisis in specific situations, such as stress or administration of certain drugs.
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  • Preoperative counseling

10.Preventative measures

Influenza vaccination: offer seasonal flu vaccination in patients with MG.
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