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NBME 21 Answers

nbme21/Block 4/Question#6

A 55-year-old man comes to the physician because of ...

Cortisol

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 +8  upvote downvote
submitted by beeip(63),

This has been a tough concept for me to get, but I think I'm finally there:

The stem is describing primary adrenal insufficiency, or Addison's.

  • ACTH is being over-produced to stimulate the adrenals to produce cortisol, but they can't respond, either due to atrophy or destruction (TB, autoimmune: DR4, etc.)
  • The first 13 amino acids of ACTH can be cleaved to form α-MSH, which stimulates melanocytes, causing hyperpigmentation
jotajota94  Good job! Also, cortisol is involved in maintaining blood pressure. which was decreased in the patient. +3  
tinydoc  Decreased Na and increase K+ --- Hypoaldosteronisim Hypoglycemia, and hypotension --- Hypocortisolism so the adrenals arent working ---- adrenal Insufficiency the Hyperpigmentation comes from the increase ACTH as ACTH is from Proopiomelanocorticotropin. SO - increased ACTH also increases a -MSH ---> Hyper pigmentation. +5  
hungrybox  thank u for this answer +  
bilzcop  Ugh! I misread the question and chose ACTH :( +  
cienfuegos  @bilzcop: same +  
cienfuegos  @bilzcop: let's never do it again, k? +  
maxillarythirdmolar  Why does this patient have elevated BUN and creatinine?? +  




 +1  upvote downvote
submitted by amirmullick3(9),

The stem is describing primary adrenal insufficiency, or Addison's.

ACTH is being over-produced to stimulate the adrenals to produce cortisol, but they can't respond, either due to atrophy or destruction (TB, autoimmune: DR4, etc.) The first 13 amino acids of ACTH can be cleaved to form α-MSH, which stimulates melanocytes, causing hyperpigmentation. Cortisol helps with BP and his is low.

Patients also have low aldosterone. Low Na and high K is a sign of hypoaldosteronism. Patients retain H and lose HCO3. Losing HCO3 causes Cl- retention in the PCT. This all leads to metabolic acidosis. Loss of cortisol causes anorexia, hypoglycemia, and a low BP as seen in this patient.





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