Adrenal Tumor Pets

Classifying Cushing's Syndrome Pituitary vs Adrenal

Adrenal or Pituitary Cushing's? Why do we Care?

Once a pet has been confirmed as having Cushing’s syndrome, the next step is to determine which form of Cushing’s syndrome the pet has since treatment is different for each form.

  • If an adrenal tumor is present, there is a 50% chance that it is a malignant tumor. Surgical exploration is generally warranted so that the tumor may be removed.
  • Adrenal tumors can be treated with medications just as pituitary tumors can be but the protocols are completely different so it is imperative that classification be complete.

So What Tests will Tell us What Type of Cushing's Syndrome is Present?

The Low Dose Dexamathasone Suppression Test
If one is lucky, the same test used to determine if Cushing’s disease is present or not can also classify the Cushing’s disease so that no further tests are needed. If a 4-hour sample is drawn in addition to the pre-dexamethasone sample and the 8-hour sample, more information can be determined about the cortisol suppression pattern. Some patterns are characteristic of pituitary or adrenal Cushing’s disease. If your pet fits into this category, then no further testing is needed to classify the Cushing’s disease.

Imaging such as ultrasound, MRI, CT scan, or nuclear medicine studies may be helpful in classifying Cushing’s syndrome. Probably ultrasound is the most readily available. If a Low Dose Dexamethasone Suppression test has confirmed Cushing’s syndrome but not confirmed which type, imaging of the adrenal glands can provide the information needed to complete classification. Two large or normal sized adrenal glands are typically present with the presence of a pituitary tumor as both adrenal glands will be equally stimulated by ACTH production. Other imaging results should be followed by either of the blood tests described below.

If one adrenal gland looks large and the other is not visible, an adrenal tumor may be suspected (remember, the non-tumorous gland will atrophy). In the event of an adrenal tumor, ultrasound is also helpful to determine the extent of tumor spread, which is crucial to deciding for or against surgical removal of the tumor.

The High Dose Dexamethazone Suppression Test
This test is similar to the low dose dexamethasone suppression test except that a higher dose of dexamethasone is used and the patient having the test is already known to have Cushing’s disease through prior testing. In this case, a patient with a pituitary tumor will show suppression in circulating cortisol when exposed to the high dose of dexamethasone (though suppression does not occur with the low dose). If an adrenal tumor is present, suppression does not occur.

Engodenous ACTH Level
This test is felt by many to be the most accurate method of classifying Cushing’s syndrome but the problem is that the test is technically challenging to run. Serum from the patient must be frozen when transported to the laboratory and may not thaw. The hormone ACTH is very fragile and may not survive the trip to the lab. The idea with this test is that a patient with a pituitary tumor will have high ACTH levels, as this is what the tumor is secreting. A patient with low or no measurable ACTH levels has an adrenal tumor as the pituitary is trying its best not to stimulate the over-active adrenal tumor.

tags: adrenal tumor pets, adrenal gland, cushings disease, pituitary gland,addison's disease, adrenal cortex, addisons disease, cushex drops, cortisol levels, symptoms of cushings, canine cushings disease, clinical signs,hair loss,canine cushings, blood tests,vetoryl trilostane,

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