Master the board step 3

Master the Boards: USMLE Step 3
Pituitary Tumor
Ectopic ACTH
Production
Adrenal Adenoma
ACTH High High Low
High-dose
dexamethasone
Suppression No suppression No suppression
Specific test
MRI
Scan chest and abdomen
Scan adrenals
Petrossal vein sampling
Treatment Removal Removal Removal
Diagnostic Testing
Lab abnormalities are as follows:
··
Hyperglycemia, hyperlipidemia
··
Osteoporosis
··
Leukocytosis
··
Metabolic alkalosis caused by increased urinary loss of H+
Basic Science Correlate
Mechanism of Metabolic Alkalosis
Cortisol has both mineralocorticoid or aldosterone effects on the kidney.
Excess adrenal steroids increase hydrogen ion excretion at the alphaintercalated
cell of the late distal/early collecting duct. Hypokalemia results
from potassium excretion through the principal cell.
Following are the best initial diagnostic tests:
24-hour cortisol testing is
more accurate (gives fewer
false positives) than 1 mg
overnight testing.
··
1 mg overnight dexamethasone suppression testing: A normal person will
suppress the 8:00 a.m. level of cortisol if given dexamethasone at 11:00 p.m.
the night before. A normal 1 mg overnight dexamethasone suppression test
excludes hypercortisolism of all kinds. An abnormal test can still be falsely
elevated from various stresses, such as these:
--
Depression
--
Alcoholism
--
Emotional or physical stress
··
24-hour urine cortisol: This test is done to confirm that an overnight dexamethasone
suppression test is not falsely abnormal. The 24-hour urine cortisol
adds specificity to the overnight test. If the overnight dexamethasone
test is abnormal (fails to suppress), then get the 24-hour urine cortisol to
confirm hypercortisolism (Cushing syndrome).
104