Question 10#
A 48-year-old woman presents with weight gain, easy bruisability, and muscle weakness. She has a 30-pack-year history of smoking. She presents with a temperature of 36.8°C, blood pressure of 144/92 mmHg, heart rate of 96 beats per minute, respiratory rate of 16 breaths per minute, and oxygen saturation of 98% on room air. Physical examination reveals the finding seen in the photo below. Laboratory studies are significant for a fasting blood glucose of 310 mg/dL, a 24-hour urine cortisol level of 1,200 μg (normal range, 10 to 100 μg), and a plasma ACTH of 126 pg/mL (normal range, 10 to 60 pg/mL). Twenty-four– hour urine cortisol level is 1,184 μg after high-dose dexamethasone is administered.
Which of the following is the cause of the patient’s symptoms and laboratory findings?
A. Exogenous steroidsB. Adrenocortical adenoma
C. Ectopic ACTH-producing tumor
D. Cushing disease
Correct Answer is C
Comment:
Ectopic ACTH-producing tumor. The patient in this question is presenting with typical symptoms of Cushing syndrome. In addition to weight gain, easy bruisability, and muscle weakness, symptoms include moon facies, truncal obesity, buffalo hump, hyperglycemia, osteoporosis, amenorrhea, and hypertension. Cushing syndrome by definition only signifies increased cortisol levels, so there must be a workup to determine the etiology of the disorder. One must first diagnose Cushing syndrome by initially screening with a 24-hour urine cortisol level. The vast majority of patients with Cushing syndrome have levels greater than 90 μg/24 hours. Once the diagnosis of Cushing syndrome has been made, the etiology must then be determined by measuring plasma ACTH level (elevated ACTH is considered greater than 20 pg/mL). (A) The most common cause of Cushing syndrome is exogenous steroids; however, this will have a low ACTH level due to the steroids negatively inhibiting secretion of ACTH from the pituitary. (B) Likewise, adrenal-related causes of Cushing syndrome such as adrenocortical adenoma will have a decreased ACTH level. Our patient, on the other hand, presents with an elevated ACTH level and so then next step is to distinguish between Cushing disease (increased ACTH secretion from a pituitary adenoma) and ectopic ACTH production, sometimes seen in small cell lung cancer. (D) High-dose dexamethasone will normally suppress urinary cortisol or serum cortisol levels in Cushing disease, but will not suppress cortisol levels in ectopic ACTH production. In this patient, 24-hour urine cortisol levels were not adequately suppressed (defined as suppressing cortisol levels by at least 50%), so ectopic ACTH production (likely small cell lung cancer given the patient’s smoking history) is the diagnosis.