Soru

A 32-year-old woman comes to the outpatient clinic reporting a 6-week history of intermittent double vision and drooping of her right eyelid. She notes that these symptoms are usually absent in the morning but become progressively more noticeable by the late afternoon and evening. Recently, she has also experienced mild difficulty chewing tough foods like steak. She has no significant past medical history and takes no medications. Vital signs are within normal limits. Neurologic examination reveals a right-sided ptosis that becomes more pronounced after the patient is asked to maintain an upward gaze for 60 seconds. Extraocular movements are notable for asymmetric limitation in both eyes, without pupillary involvement. Strength in the proximal and distal extremities is intact, and deep tendon reflexes are normal bilaterally. Which of the following is the most appropriate next step in the diagnostic evaluation?