Diagnosis of Cushing's syndrome
Diagnostic Test list for Cushing's syndrome:
The list of medical tests
mentioned in various sources as
used in the diagnosis of Cushing's syndrome
includes:
Cushing's syndrome Diagnosis: Book Excerpts
Tests and diagnosis discussion for Cushing's syndrome:
Diagnosis is based on a review of the patient's
medical history, physical examination and laboratory tests. Often x-ray
exams of the adrenal or pituitary glands are useful for locating tumors.
These tests help to determine if excess levels of cortisol are present and
why.
24-Hour Urinary Free Cortisol Level
This is the most specific
diagnostic test. The patient's urine is collected over a 24-hour period
and tested for the amount of cortisol. Levels higher than 50-100
micrograms a day for an adult suggest Cushing's syndrome. The normal upper
limit varies in different laboratories, depending on which measurement
technique is used.
Once Cushing's syndrome has been diagnosed, other tests are used to
find the exact location of the abnormality that leads to excess cortisol
production. The choice of test depends, in part, on the preference of the
endocrinologist or the center where the test is performed.
Dexamethasone Suppression Test
This test helps to distinguish
patients with excess production of ACTH due to pituitary adenomas from
those with ectopic ACTH-producing tumors. Patients are given
dexamethasone, a synthetic glucocorticoid, by mouth every 6 hours for 4
days. For the first 2 days, low doses of dexamethasone are given, and for
the last 2 days, higher doses are given. Twenty-four hour urine
collections are made before dexamethasone is administered and on each day
of the test. Since cortisol and other glucocorticoids signal the pituitary
to lower secretion of ACTH, the normal response after taking dexamethasone
is a drop in blood and urine cortisol levels. Different responses of
cortisol to dexamethasone are obtained depending on whether the cause of
Cushing's syndrome is a pituitary adenoma or an ectopic ACTH-producing
tumor.
The dexamethasone suppression test can produce false-positive results
in patients with depression, alcohol abuse, high estrogen levels, acute
illness, and stress. Conversely, drugs such as phenytoin and phenobarbital
may cause false-negative results in response to dexamethasone suppression.
For this reason, patients are usually advised by their physicians to stop
taking these drugs at least one week before the test.
CRH Stimulation Test
This test helps to distinguish between
patients with pituitary adenomas and those with ectopic ACTH syndrome or
cortisol-secreting adrenal tumors. Patients are given an injection of CRH,
the corticotropin-releasing hormone which causes the pituitary to secrete
ACTH. Patients with pituitary adenomas usually experience a rise in blood
levels of ACTH and cortisol. This response is rarely seen in patients with
ectopic ACTH syndrome and practically never in patients with
cortisol-secreting adrenal tumors.
Direct Visualization of the Endocrine Glands (Radiologic
Imaging)
Imaging tests reveal the size and shape of the pituitary
and adrenal glands and help determine if a tumor is present. The most
common are the CT (computerized tomography) scan and MRI (magnetic
resonance imaging). A CT scan produces a series of x-ray pictures giving a
cross-sectional image of a body part. MRI also produces images of the
internal organs of the body but without exposing the patient to ionizing
radiation.
Imaging procedures are used to find a tumor after a diagnosis has been
established. Imaging is not used to make the diagnosis of Cushing's
syndrome because benign tumors, sometimes called "incidentalomas," are
commonly found in the pituitary and adrenal glands. These tumors do not
produce hormones detrimental to health and are not removed unless blood
tests show they are a cause of symptoms or they are unusually large.
Conversely, pituitary tumors are not detected by imaging in almost 50
percent of patients who ultimately require pituitary surgery for Cushing's
syndrome.
Petrosal Sinus Sampling
This test is not always required, but
in many cases, it is the best way to separate pituitary from ectopic
causes of Cushing's syndrome. Samples of blood are drawn from the petrosal
sinuses, veins which drain the pituitary, by introducing catheters through
a vein in the upper thigh/groin region, with local anesthesia and mild
sedation. X-rays are used to confirm the correct position of the
catheters. Often CRH, the hormone which causes the pituitary to secrete
ACTH, is given during this test to improve diagnostic accuracy. Levels of
ACTH in the petrosal sinuses are measured and compared with ACTH levels in
a forearm vein. ACTH levels higher in the petrosal sinuses than in the
forearm vein indicate the presence of a pituitary adenoma; similar levels
suggest ectopic ACTH syndrome.
The Dexamethasone-CRH Test
Some individuals have high
cortisol levels, but do not develop the progressive effects of Cushing's
syndrome, such as muscle weakness, fractures and thinning of the skin.
These individuals may have Pseudo Cushing's syndrome, which was originally
described in people who were depressed or drank excess alcohol, but is now
known to be more common. Pseudo Cushing's does not have the same long-term
effects on health as Cushing's syndrome and does not require treatment
directed at the endocrine glands. Although observation over months to
years will distinguish Pseudo Cushing's from Cushing's, the
dexamethasone-CRH test was developed to distinguish between the conditions
rapidly, so that Cushing's patients can receive prompt treatment. This
test combines the dexamethasone suppression and the CRH stimulation tests.
Elevations of cortisol during this test suggest Cushing's syndrome.
(Source: excerpt from Cushing's Syndrome: NIDDK)
Diagnostic Tests for Cushing's syndrome: Online Medical Books
16 MEDICAL BOOKS ONLINE!
Review excerpts from medical books online, free, without registration,
for more information about diagnostis of Cushing's syndrome.
Cushing's syndrome:
Diagnosis
(Professional Guide to Diseases (Eighth Edition))
Initially, diagnosis of Cushing’s syndrome requires determination of plasma steroid levels. In people with normal hormone balance, plasma cortisol levels are higher in the morning and decrease gradually throughout the day (diurnal variation). In patients with Cushing’s syndrome, cortisol levels don’t fluctuate and typically remain consistently elevated; 24-hour urine sample demonstrates elevated free cortisol levels.
Confirming diagnosis A low-dose dexamethasone suppression test confirms the diagnosis of Cushing’s syndrome. Salivary cortisol levels collected at midnight (usually performed on an outpatient basis) are elevated and are the most sensitive confirmatory test. (See Diagnosing Cushing’s syndrome.)
A high-dose dexamethasone suppression test can determine if Cushing’s syndrome results from pituitary dysfunction (Cushing’s disease). In this test, dexamethasone suppresses plasma cortisol levels, and urinary 17-hydroxycorticosteroid (17-OHCS) and 17-ketogenic steroid levels fall to 50% or less of basal levels. Failure to suppress these levels indicates that the syndrome results from an adrenal tumor or a nonendocrine, corticotropin-secreting tumor. This test can produce false-positive results.
In a stimulation test, administration of metyrapone, which blocks cortisol production by the adrenal glands, tests the ability of the pituitary gland and the hypothalamus to detect and correct low levels of plasma cortisol by increasing corticotropin production. The patient with Cushing’s disease reacts to this stimulus by secreting an excess of plasma corticotropin as measured by levels of urinary 17-OHCS. If the patient has an adrenal or a nonendocrine corticotropin-secreting tumor, the pituitary gland — which is suppressed by the high cortisol levels — can’t respond normally, so steroid levels remain stable or fall.
Ultrasound, computed tomography (CT) scan, or angiography localizes adrenal tumors; CT scan and magnetic resonance imaging of the head may identify pituitary tumors.
» READ BOOK EXCERPT ONLINE »
Source: Professional Guide to Diseases (Eighth Edition), 2005
Cushing's syndrome:
Diagnosis
(Handbook of Diseases)
Initially, the diagnosis of Cushing’s syndrome requires determination of plasma steroid levels. In persons with normal hormone balance, plasma cortisol levels are higher in the morning and decrease gradually through the day (diurnal variation). In patients with Cushing’s syndrome, cortisol levels don’t fluctuate and typically remain consistently elevated; a 24-hour urine sample demonstrates elevated free cortisol levels.
Suppression test
A low-dose dexamethasone suppression test confirms the diagnosis of Cushing’s syndrome. A high-dose dexamethasone suppression test can determine whether Cushing’s syndrome results from pituitary dysfunction (Cushing’s disease) or from adenoma of the adrenal gland or ectopic corticotropin secretion.
In this test, dexamethasone suppresses plasma cortisol levels, and urinary 17-hydroxycorticosteroids (17-OHCS) and 17-ketogenic steroids fall to 50% or less of basal levels. Failure to suppress these levels indicates that the syndrome results from an adrenal tumor or a nonendocrine, corticotropin-secreting tumor. This test can produce false-positive results.
Stimulation test
In a stimulation test, administration of metyrapone, which blocks cortisol production by the adrenal glands, tests the ability of the pituitary gland and the hypothalamus to detect and correct low levels of plasma cortisol by increasing corticotropin production. The patient with Cushing’s syndrome reacts to this stimulus by secreting an excess of plasma corticotropin as measured by levels of urinary 17-OHCS.
If the patient has an adrenal or a nonendocrine corticotropin-secreting tumor, the pituitary gland—which is suppressed by the high cortisol levels — can’t respond normally, so steroid levels remain stable or fall. The corticotropin-releasing hormone tests can also be used to help differentiate pituitary Cushing’s and ectopic corticotropin syndrome.
Other tests
Ultrasonography, a computed tomography (CT) scan, magnetic resonance imaging (MRI), or angiography localizes adrenal tumors; a CT scan and MRI of the head identify pituitary tumors.
Clinical tip Measuring resting cortisol at midnight is the most sensitive test. This can be done at home by collecting saliva at midnight. In the hospital, collecting serum from an indwelling catheter placed in the early evening may aid collection.
» READ BOOK EXCERPT ONLINE »
Source: Handbook of Diseases, 2003
What causes cancer and why is it so hard to treat? Leading experts provide an overview of cancer, from what goes wrong in a cell's genetic...
Whenever you go to a hospital or clinic for a major procedure or diagnostic test, one of the many forms you are given to sign is an "informed...
Sexual contact can sometimes result in problems. An unwanted pregnancy or sexually transmitted diseases may be some of those consequences. But by...
Sleep is necessary to feel refreshed, but now we know sleep actually impacts the way the body functions. Sleeping poorly can affect how often you get...
See full list of 4 related videos
» Next page: Signs of Cushing's syndrome
Rate This Website
What do you think about the features of this website?
Take our user survey and have your say:
Website User Survey
Medical Tools & Articles:
Next articles:
Tools & Services:
Medical Articles:
Forums & Message Boards
- Ask or answer a question at the Boards:
