A 60-year-old man with a 20-year smoking history is brought to the physician by his daughter because of altered behavior over the past week. She says that her father’s personality has changed. He has had a productive cough over the past month, for which he is taking over-the-counter medications. He is not a drug addict, diabetetic or hypertensive. Physical examination shows multiple bruises on the skin and hyper-pigmented spots on the buccal mucosa and the back of his neck. His blood pressure is 160/90 mmHg, and pulse is 70/mm. Laboratory studies show random blood sugar of 224 mg/dL, serum sodium of 140 mEq/L, serum potassium of 2.0 mEq/L, and serum bicarbonate of 27 mEq/L.
Which of the following tests is most likely to be abnormal in this patient?
A 60-year-old man with a 20-year smoking history is brought to the physician by his daughter because of altered behavior over the past week. She says that her father’s personality has changed. He has had a productive cough over the past month, for which he is taking over-the-counter medications. He is not a drug addict, diabetetic or hypertensive. Physical examination shows multiple bruises on the skin and hyper-pigmented spots on the buccal mucosa and the back of his neck. His blood pressure is 160/90 mmHg, and pulse is 70/mm. Laboratory studies show random blood sugar of 224 mg/dL, serum sodium of 140 mEq/L, serum potassium of 2.0 mEq/L, and serum bicarbonate of 27 mEq/L.
Which of the following tests is most likely to be abnormal in this patient?
💡 Explanation
**Core Concept**
The underlying principle being tested involves the diagnosis of a condition characterized by hyperpigmentation, hypokalemia, and hypertension, with a possible link to an endocrine disorder, given the patient's altered behavior, productive cough, and recent onset of hyperglycemia.
**Why the Correct Answer is Right**
The patient's presentation of hyperpigmentation, hypokalemia, and hypertension, along with recent onset of hyperglycemia and altered mental status, suggests a diagnosis of **Cushing's syndrome**. This condition is characterized by an excess of cortisol, which can be due to various causes including a pituitary adenoma, adrenal tumor, or ectopic production of adrenocorticotropic hormone (ACTH) by a tumor, such as small cell carcinoma of the lung, given the patient's smoking history.
**Why Each Wrong Option is Incorrect**
**Option A:** Would be incorrect as it does not directly relate to the combination of symptoms presented, particularly the hyperpigmentation and hypokalemia.
**Option B:** Might seem plausible due to the patient's smoking history and productive cough, but it does not directly explain the metabolic and electrolyte abnormalities.
**Option C:** Could be a consideration in a patient with hypertension and hypokalemia, but it doesn't account for the hyperpigmentation and the acute change in behavior.
**Option D:** Is the correct answer choice related to the diagnosis of Cushing's syndrome, given the clinical presentation.
**Clinical Pearl / High-Yield Fact**
A key point to remember is that **ectopic ACTH-producing tumors** can cause Cushing's syndrome and are more likely to present with very high levels of ACTH and severe hypokalemia, as seen in this patient. The presence of hyperpigmentation is also a clue towards an ectopic source of ACTH, as it stimulates melanocortin 1 receptors.
**Correct Answer:** D. ACTH level
✓ Correct Answer: A. CT chest
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