Small Cell Lung Cancer with Pigmentation?

Your correct. ACTH comes from POMC which also makes MSH.

So, my understanding is the following:

Hyerpigmentation:

Addisions Disease: yes

ACTH producing Adenoma: yes

ectopic ACTH: NO

It has to be made in the pituitary for from the POMC precursor to have skin hyperpigmentation.

Edit:

"About 10% of cases are due to nonpituitary ACTH-secreting neoplasms (eg, small cell lung carcinoma), which produce excessive amounts of ectopic ACTH. Hypokalemia and hyperpigmentation are commonly found in this group." -- Current Medical Diagnosis and Treatment 49th Ed.

"In ectopic ACTH syndrome, hypokalemic metabolic alkalosis and muscle weakness are usually the predominant manifestations, although clinical and laboratory features may be subtle, such as glucose intolerance, mild hypertension, hyperpigmentation, and hirsutism. Physical changes such as moon facies, "buffalo hump," and striae are uncommon, perhaps because of the relatively short survival of these patients. SCLC is the cell type most frequently associated with ectopic ACTH syndrome. ACTH levels are very high and, unlike in classic Cushing's syndrome associated with pituitary adenoma, ACTH levels are not suppressible by high doses of dexamethasone. Like SIADH, the ectopic ACTH syndrome is best managed by effective therapy for the underlying disease; however, severe hypokalemia or hypertension may occur and requires immediate treatment." -- Internal Medicine, Stein 5th Ed.

POMC makes a) ACTH and b) Beta lipotropins--> beta MSH and beta-endorphins. ACTH also has a an alpha MSH subunit as part of its structure. Now, if the ectopic ACTH has same structure, there will be hyperpigmentation due to alpha MSH.

drsh1 said:

POMC makes a) ACTH and b) Beta lipotropins--> beta MSH and beta-endorphins. ACTH also has a an alpha MSH subunit as part of its structure. Now, if the ectopic ACTH has same structure, there will be hyperpigmentation due to alpha MSH.

Click to expand...

This is correct; just studied it.

in ectopic acth production, the syndrome typically hasn't been long-standing enough to produce the hyperpigmentation. of course, it can happen as is mentioned above

According to Step 2 UW (question ID: 2173), in the vignette "Skin Examination shows hyperpigmentation in exposed areas" and correct answer was Ectopic ACTH production.

But just thinking of the pathophysiology it confuses me, as I would expect Ectopic ACTH to suppress endogenous production of POMC --> ACTH + bMSH. Unless, this is the same exact biochemical reaction/method of production in a tumor?

"In ectopic ACTH syndrome, hyperpigmentation of knuckles , scars , and or skin areas exposed to increased friction can be observed , and is caused by STIMULATORY EFFECTS OF EXCESS ACTH AND OTHER POMC CLEAVAGE PRODUCTS on melanocyte pigment production"
--Harrison