Case 9 Nephrology

Rapid Weight Gain

Work it one clue at a time. The diagnosis stays hidden until you reveal it.

Clue 1

A young man comes to your clinic for evaluation of rapid weight gain. He has heard “diet and exercise” several times before he sees you.

Clue 2

The driver license photo was taken ~9 months prior.

You make some observations, leading you to generate a hypothesis.

Based on your hypothesis, you examine the patient further. And you make several more important observations, increasing the likelihood of your hypothesis.

Clue 3

Clue 4

Clue 5

You remember that skin thickness can be an important sign in this condition, from Lynn Loriaux’s 2017 @NEJM review.

(Examiner’s hand is shown above, patient’s below.)

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Clue 6

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Clue 7

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Clue 8

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You now have a clinical syndrome that is consistent with Cushing’s syndrome.

A confirmatory test is your next step.

Urine free cortisol (confirmatory test): 7,960 mcg/24H (!)

Clue 9

You have now confirmed the diagnosis of Cushing’s syndrome. The next question is, is it ACTH-dependent or ACTH-independent?

A plasma ACTH level is necessary to make this determination.

Plasma ACTH level is 496 pg/mL (normal <50)

Where is that ACTH coming from? The pituitary gland (ectopic) or elsewhere (ectopic)?

To determine this, inferior petrosal sinus sampling is necessary.

IPSS shows a ratio <3, confirming an ectopic source of ACTH.

Clue 10

Clue 11

Chest imaging ultimately reveals the presence of a bronchial carcinoid tumor.

Clue 12

You have diagnosed ACTH-dependent Cushing’s syndrome from an ectopic source using only your eyes and hypothesis-driven laboratory and imaging tests.

End of case.