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Emergency and Acute Medicine – Myasthenia Gravis
Myasthenia gravis (MG) is an antibody-mediated autoimmune disorder characterized by painless, fluctuating, and fatigable skeletal muscle weakness. Weakness typically worsens with repeated activity and improves with rest. The disease may present in an ocular form or as generalized myasthenia gravis. Ocular involvement, affecting the eyelids and extraocular muscles, is the most common initial presentation and accounts for approximately 60% of cases. Although symptoms may initially be limited to the eyes, nearly 80% of patients with ocular MG will progress to generalized disease within two years.
Generalized myasthenia gravis involves proximal limb muscles, axial musculature, and bulbar muscles, including those responsible for speech, chewing, and swallowing. The disease often follows an acute or subacute course with relapses and remissions. Thymic abnormalities are common, with thymic hyperplasia present in approximately 65% of patients and thymoma in about 15%. A life-threatening complication, known as myasthenic crisis, occurs when respiratory muscle weakness or bulbar dysfunction leads to respiratory failure or inability to protect the airway. Common triggers include infection, surgery, trauma, pregnancy, and medication changes, particularly rapid tapering of corticosteroids.
The pathophysiology of myasthenia gravis involves antibodies directed against nicotinic acetylcholine receptors at the neuromuscular junction, resulting in impaired neuromuscular transmission. Up to 20% of patients may be seronegative for acetylcholine receptor antibodies. Certain medications can induce or worsen myasthenic weakness, including aminoglycosides, macrolides, fluoroquinolones, beta-blockers, calcium-channel blockers, anticonvulsants, antipsychotics, and neuromuscular blocking agents. Penicillamine is a well-recognized cause of drug-induced MG.
Clinically, patients report fluctuating weakness that worsens with activity. Ocular symptoms include ptosis and diplopia, often noted during prolonged visual tasks such as reading or driving. Bulbar involvement leads to slurred or nasal speech, difficulty chewing, swallowing, and maintaining jaw closure. Limb weakness commonly affects proximal muscles, causing difficulty climbing stairs, rising from a seated position, or lifting objects overhead. On physical examination, ptosis, diplopia, and facial weakness may be evident, while reflexes and sensation remain normal. Repetitive testing of affected muscle groups typically reproduces weakness.
Emergency evaluation focuses on identifying respiratory compromise and precipitating factors such as infection. Diagnostic testing includes basic laboratory studies, thyroid function tests, and antibody testing for acetylcholine receptor antibodies. Imaging of the chest with CT is essential to evaluate for thymoma. Bedside diagnostic tools include the ice test, in which application of ice to the eyelid transiently improves ptosis, supporting the diagnosis. The edrophonium (Tensilon) test may produce short-lived improvement in strength but requires cardiac monitoring and atropine availability due to the risk of bradycardia and increased secretions.
Management in the emergency setting prioritizes airway protection and respiratory support. Patients in myasthenic crisis require early intubation and mechanical ventilation. Objective indicators of impending respiratory failure include reduced vital capacity and weak inspiratory pressures. In crisis, acetylcholinesterase inhibitors are typically withheld, and treatment includes plasmapheresis or intravenous immunoglobulin (IVIG), along with high-dose corticosteroids. Infections and other triggers must be identified and treated aggressively. Atropine may be used to counteract muscarinic effects in suspected cholinergic crisis.
Hospital admission is required for new-onset disease, diagnostic uncertainty, worsening weakness, or any evidence of respiratory compromise. Intensive care admission is mandatory for myasthenic crisis or borderline respiratory status. Patients who demonstrate improvement and have stable respiratory function may be discharged in consultation with neurology, with close outpatient follow-up arranged.
A key clinical pearl is that any patient with known myasthenia gravis presenting to the emergency department should be carefully evaluated for signs of myasthenic crisis and secondary precipitants. Early recognition and aggressive supportive management are essential to prevent respiratory failure and improve outcomes.
Myasthenia gravis (MG) is an antibody-mediated autoimmune disorder characterized by painless, fluctuating, and fatigable skeletal muscle weakness. Weakness typically worsens with repeated activity and improves with rest. The disease may present in an ocular form or as generalized myasthenia gravis. Ocular involvement, affecting the eyelids and extraocular muscles, is the most common initial presentation and accounts for approximately 60% of cases. Although symptoms may initially be limited to the eyes, nearly 80% of patients with ocular MG will progress to generalized disease within two years.
Generalized myasthenia gravis involves proximal limb muscles, axial musculature, and bulbar muscles, including those responsible for speech, chewing, and swallowing. The disease often follows an acute or subacute course with relapses and remissions. Thymic abnormalities are common, with thymic hyperplasia present in approximately 65% of patients and thymoma in about 15%. A life-threatening complication, known as myasthenic crisis, occurs when respiratory muscle weakness or bulbar dysfunction leads to respiratory failure or inability to protect the airway. Common triggers include infection, surgery, trauma, pregnancy, and medication changes, particularly rapid tapering of corticosteroids.
The pathophysiology of myasthenia gravis involves antibodies directed against nicotinic acetylcholine receptors at the neuromuscular junction, resulting in impaired neuromuscular transmission. Up to 20% of patients may be seronegative for acetylcholine receptor antibodies. Certain medications can induce or worsen myasthenic weakness, including aminoglycosides, macrolides, fluoroquinolones, beta-blockers, calcium-channel blockers, anticonvulsants, antipsychotics, and neuromuscular blocking agents. Penicillamine is a well-recognized cause of drug-induced MG.
Clinically, patients report fluctuating weakness that worsens with activity. Ocular symptoms include ptosis and diplopia, often noted during prolonged visual tasks such as reading or driving. Bulbar involvement leads to slurred or nasal speech, difficulty chewing, swallowing, and maintaining jaw closure. Limb weakness commonly affects proximal muscles, causing difficulty climbing stairs, rising from a seated position, or lifting objects overhead. On physical examination, ptosis, diplopia, and facial weakness may be evident, while reflexes and sensation remain normal. Repetitive testing of affected muscle groups typically reproduces weakness.
Emergency evaluation focuses on identifying respiratory compromise and precipitating factors such as infection. Diagnostic testing includes basic laboratory studies, thyroid function tests, and antibody testing for acetylcholine receptor antibodies. Imaging of the chest with CT is essential to evaluate for thymoma. Bedside diagnostic tools include the ice test, in which application of ice to the eyelid transiently improves ptosis, supporting the diagnosis. The edrophonium (Tensilon) test may produce short-lived improvement in strength but requires cardiac monitoring and atropine availability due to the risk of bradycardia and increased secretions.
Management in the emergency setting prioritizes airway protection and respiratory support. Patients in myasthenic crisis require early intubation and mechanical ventilation. Objective indicators of impending respiratory failure include reduced vital capacity and weak inspiratory pressures. In crisis, acetylcholinesterase inhibitors are typically withheld, and treatment includes plasmapheresis or intravenous immunoglobulin (IVIG), along with high-dose corticosteroids. Infections and other triggers must be identified and treated aggressively. Atropine may be used to counteract muscarinic effects in suspected cholinergic crisis.
Hospital admission is required for new-onset disease, diagnostic uncertainty, worsening weakness, or any evidence of respiratory compromise. Intensive care admission is mandatory for myasthenic crisis or borderline respiratory status. Patients who demonstrate improvement and have stable respiratory function may be discharged in consultation with neurology, with close outpatient follow-up arranged.
A key clinical pearl is that any patient with known myasthenia gravis presenting to the emergency department should be carefully evaluated for signs of myasthenic crisis and secondary precipitants. Early recognition and aggressive supportive management are essential to prevent respiratory failure and improve outcomes.
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