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Acute ED management of these disorders centers on the care of acute respiratory failure as the most notable complication.
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Amyotrophic lateral sclerosis (ALS) causes progressive muscle atrophy and weakness. Upper motor neuron dysfunction causes limb spasticity, hyperreflexia, and emotional liability. Lower neuron dysfunction causes limb muscle weakness, atrophy, fasciculations, dysarthria, dysphagia, and difficulty in mastication. Symptoms are asymmetric. Patients may appear to have an acute compressive radiculopathy. Respiratory muscle weakness causes progressive respiratory depression.
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Diagnosis and Differential
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The diagnosis is suggested by upper and lower motor neuron dysfunction without other central nervous system dysfunction. The differential includes myasthenia gravis, diabetes, thyroid dysfunction, vitamin B12 deficiency, lead toxicity, vasculitis, and CNS or spinal cord tumors.
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Emergency Department Care and Disposition
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Respiratory failure, pneumonia, choking, and trauma are the common ED presentations. Optimize pulmonary function with nebulizer treatments, steroids, antibiotics, and intubation, as indicated. Admit patients with pneumonia or inability to handle secretions.
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Myasthenia gravis (MG) is characterized by muscle weakness and fatigue. Most MG patients have weakness of the proximal extremity muscles, neck extensors, and facial or bulbar muscles. Ptosis and diplopia are common presenting symptoms; 10% of patients have ocular muscle weakness only. Symptoms worsen as the day progresses and improve with rest. Severe respiratory muscle weakness causing respiratory failure is seen in myasthenic crisis.
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Diagnosis and Differential
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The differential for MG includes Lambert-Eaton, thyroid disorders, and stroke. MG is confirmed through administration of edrophonium, electromyogram, and serum testing for acetylcholine receptor antibodies. The edrophonium (Tensilon) test can differentiate a myasthenic crisis (inadequate treatment) from a cholinergic crisis (overmedication). Edrophonium has a rapid onset and short duration of action. First, a test dose of 1 to 2 milligrams IV is given and, if symptoms such as muscle weakness or respiratory depression worsen (cholinergic crisis), then the test is stopped. Emergent intubation may be necessary. Otherwise, the test is considered positive, indicating myasthenic crisis. Edrophonium can cause bradycardia, which responds to atropine.
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Emergency Department Care and Disposition
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MG is treated with airway management, avoidance of drugs that worsen MG, and administration of acetylcholinesterase inhibitors, high-dose steroids, plasmapheresis, or IV immunoglobulins.
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Administer supplemental oxygen. Etomidate can be used if rapid sequence intubation is considered. Avoid depolarizing or nondepolarizing paralytic agents.
If the Tensilon test is positive, neostigmine should be given (0.5 to 2 milligrams IM, IV, SC or increments of 15 milligrams po). MG patients treated for other concerns should receive their usual cholinergic inhibitors.
Many drugs can exacerbate MG. Check carefully for drug interactions. Consult with a neurologist to aid in decision-making (Table 147-1).
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