A 19-year-old man is evaluated in the emergency department for weakness and inability to walk that began shortly after a 5-mile run. In the morning, he had a related episode of weakness of both lower limbs that lasted for 1 hour and resolved spontaneously. He also notes about a 5.0-kg (11-lb) weight loss over the past 7 months, episodes of palpitations, and heat intolerance. He was previously in good health. He takes no medications.
On physical examination, blood pressure is 150/90 mm Hg, pulse rate is 106/min, and respiration rate is 20/min. BMI is 18. The thyroid is enlarged. There is a fine tremor of the outstretched hands. There is symmetric muscle weakness with areflexia in the lower and upper extremities. The remainder of the examination is unremarkable.
Electrolytes: | |
Sodium | 142 mEq/L (142 mmol/L) |
Potassium | 2.0 mEq/L (2.0 mmol/L) |
Chloride | 104 mEq/L (104 mmol/L) |
Bicarbonate | 24 mEq/L (24 mmol/L) |
Which of the following is the most likely diagnosis?