A 63-year-old man with a history of thyroid cancer presents to the emergency department with a 4-day history of generalized weakness and lack of interest in food or drink. He has no history of recent falls and he denies any pain, heart palpitations, vomiting and/or diarrhea, focal weakness, syncope, or other complaints.

Vital Signs and Physical Examination

The patient’s vital signs are normal except for low blood pressure (102/52 mm Hg) and a pulse rate of 118 beats per minute. Initial physical examination is otherwise normal except for dry mouth and an appearance of generalized weakness. An electrocardiogram (ECG), chest radiograph, and blood work are ordered. The ECG shows signs of sinus tachycardia but no acute cor pulmonale or heart strain. Laboratory results are in general within normal range (serum urea nitrogen/creatinine ratio, sodium and hemoglobin levels, and white blood cell count) and not indicative of any acute disease. Urinalysis indicates dehydration. Chest radiographs show no abnormal discovery.

Can you diagnose this condition? What additional test should you perform to confirm the diagnosis?

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