Weakness and Dyspnea in a Young Man

A 34-year-old man presents to the emergency department with progressive, generalized weakness and shortness of breath that began 2 weeks earlier. He has no history of cardiac disorders, and he denies chest pain, palpitations, and abdominal pain. He admits to recent methamphetamine use. The patient is in moderate distress. Heart rate is 152 beats per minute and regular; respiration rate, 24 breaths per minute; blood pressure, 142/68 mm Hg. Pulse oximetry shows that oxygen saturation is 95% on room air. Lungs are clear. A 2/6 systolic murmur is audible. Abdomen is soft and nontender. Neurologic examination demonstrates mild diffuse symmetric weakness.