A 27-year-old woman complains of double vision and fatigue at the end of the day. Further history reveals difficulty in chewing food, and some weakness in climbing stairs. She has stopped running because of easy leg fatigue and leg weakness. The symptoms improve with resting.On examination, there is weakness of the eyelids, masticatory muscles, and thigh flexors. Her handgrip decreases with repetitive action. There is no sensory abnormality, and reflexes are normal. Which of the following is the most likely diagnosis?
Correct Answer: myasthenia gravis
Description: The most common presenting symptoms relate to weakness of eye muscles, causing ptosis or diplopia. Difficulty in chewing, dysarthria, and dysphagia are also common. The differential diagnosis includes all diseases that cause weakness of oropharyngeal or limb muscles. These include the muscular dystrophies, ALS, and progressive bulbar palsies, among others. Most other conditions do not improve after injection of edrophonium or neostigmine, which can help differentiate myasthenia from other neuromuscular disorders. Hypercalcemia can cause weakness, but the symptoms are constant, and do not worsen with use or improve with rest. Multiple sclerosis causes focal neurologic deficits and not diffuse muscle weakness, and thyroid storm can cause a myopathy but again the weakness is constant and more prominent in proximal muscle groups.
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