A 68-year-old man presents to the neurology clinic with a 2-month history of double vision and drooping of his right eyelid. He reports that the symptoms are minimal in the morning but worsen significantly by the evening, often preventing him from reading or watching television. He also describes a feeling of “heaviness” in his head and recent difficulty chewing tough meats like steak, stating his jaw “gets tired” halfway through the meal. He denies sensory disturbances, limb numbness, or bowel and bladder dysfunction. Two weeks ago, his primary care physician prescribed ciprofloxacin for a urinary tract infection, after which he noted a marked deterioration in his ocular symptoms and new mild shortness of breath. His past medical history includes hypertension and hyperlipidemia, for which he takes lisinopril and atorvastatin. He denies tobacco or alcohol use.

He appears well-nourished but anxious. He is afebrile. His blood pressure is 135/82 mmHg with a heart rate of 78 bpm and a respiratory rate of 18 breaths per minute.