CLINICAL CASES
445
Dexamethasone suppression test: An overnight test used to screen
patients for Cushing syndrome by administering dexamethasone to a
patient. Positive results for this test are indicated by a patient’s inability
to reduce cortisol levels after dexamethasone treatment—usually
because the patient’s feedback loop mechanism is ineffective at inhibit-
ing cortisol release.
Ecchymosis: Bruise or contusion; normally comes from damage to the cap-
illaries at the site of injury, allowing blood to seep out into the sur-
rounding tissue, presenting initially as a blue or purple color.
Ectopic ACTH syndrome: Form of Cushing syndrome in which benign or
malignant tumors arise in places other than the pituitary, leading to
excessive release of ACTH and subsequently, cortisol into the bloodstream;
represents approximately 10 to 15 percent of Cushing syndrome cases.
Hirsutism: Increased presence of hair in women on body regions where
hair does not normally grow.
Hypercortisolism: A condition in which the body is exposed to an excess
of cortisol for an extended period of time.
Iatrogenic Cushing syndrome: Condition in which all symptoms of
Cushing syndrome are brought on by administration of synthetic forms
of cortisol, such as prednisone and dexamethasone. “Iatrogenic” origi-
nates from Greek and literally translates to mean “born from” the
“healer.”
Pseudo-Cushing syndrome: Condition in which alcohol induces symp-
toms of Cushing syndrome without the tumor that leads to increased cor-
tisol levels.
D ISC U SSIO N
Cortisol is a stress hormone released in response to trauma—physical and
emotional—that leads to several physiologic changes aimed at reducing the
stress associated with this trauma. This process is helpful to the body because
the activity of cortisol can limit the harmful effects of stress. However, if too
much cortisol is secreted (hypercortisolism) symptoms of Cushing syndrome
may appear.
Cortisol is secreted from the adrenal glands of the kidneys (“adrenal” liter-
ally means near or at the kidney). All steroid hormones are synthesized from
cholesterol, with the rate-limiting step in steroid biosynthesis being the cleav-
age of the cholesterol side chain. This is done by several enzymes that make
up the cytochrome P450 side-chain cleavage complex. High levels of Ca2+ and
protein phosphorylation—due to increased cAMP in the cytosol—increase the
rate of cholesterol side-chain cleavage in the mitochondria. First, cholesterol
is mobilized into the mitochondria of the adrenal cortex cells, where its side
chain is cleaved by the cytochrome P450 cleavage complex
(CYP11A1)
to yield pregnenolone (Figure 50-1). Pregnenolone is oxidized by 3P-
hydroxysteroid dehydrogenase to form progesterone, which is then converted
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