THE CASE
A 27-year-old man with no past medical history presented to his primary care physician (PCP) for a routine physical. He reported experiencing muscle weakness and fatigue for the previous 1 to 2 months. Two blood pressure measurements were recorded: 138/80 mm Hg and 142/95 mm Hg. The patient was given a diagnosis of hypertension and started on triamterene/hydrochlorothiazide. Labwork was ordered, including a complete metabolic panel, lipid panel, urinalysis, thyroid-stimulating hormone (TSH) plus thyroxine (T4), HIV antibodies, and a complete blood count.
The samples were drawn 1 week later, and the results were notable for low-normal TSH with a T4 of 0.8 ng/dL (normal range, 0.9-2.3 ng/dL); sodium, 151 mmol/L (normal range, 136-145 mmol/L); potassium, 3.4 mmol/L (normal range, 3.6-5.2 mmol/L); and white blood cell count, 13.8 x 103/mcL. The electrolyte abnormalities were attributed to the triamterene/hydrochlorothiazide, which was stopped. One week later, repeat labs showed a persistent potassium level of 3.0 mmol/L; sodium, 141 mmol/L; and glucose, 310 mg/dL. Follow-up A1C was measured at 7.4%.
At the next appointment (2 weeks after initial evaluation), the patient received a diagnosis of type 2 diabetes in addition to new-onset essential hypertension. He expressed surprise at his diagnoses, as he said he primarily ate a balanced diet with plenty of vegetables and lots of healthy home-cooked meals. His body mass index (BMI) was in normal range, and he said he exercised regularly.
The patient was started on metformin 500 mg/d and referred to Endocrinology. After seeing the endocrinologist, who agreed with metformin for initial management, the patient contacted his PCP with concerns about worsening “muscle wasting.” Based on these ongoing symptoms, the patient was advised to go to the emergency department (ED).
In the ED, the patient reported muscle aches and weakness, weight gain, dyspnea on exertion, and polyuria. He also said that his face had widened with his weight gain, and his weakness was greatest in his thighs compared to his distal lower extremities. Labs drawn in the ED indicated hyperglycemia (glucose, 334 mg/dL) and severe hypokalemia (potassium, 2.2 mmol/L).
THE DIAGNOSIS
The patient was admitted in the afternoon for further evaluation, and a random serum cortisol measurement was ordered. The results showed an elevated cortisol level (55.2 mcg/dL; normal range, 3-20 mcg/dL). This was followed by a profoundly positive low-dose dexamethasone suppression test with a morning cortisol level of 75.9 mcg/dL (normal range, < 1.8 mcg/dL). With these findings, the diagnosis of Cushing syndrome was made and the focus of the evaluation shifted to localization.
An adrenocorticotropic hormone (ACTH) measurement was ordered, as well as magnetic resonance imaging (MRI) of the pituitary gland and of the abdomen to assess the adrenal glands. Both MRIs were negative, prompting a high-dose 8-mg dexamethasone suppression test to be performed. The patient’s morning cortisol level remained elevated (69.9 mcg/dL), confirming the diagnosis of Cushing syndrome.
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