Q My old dachshund cannot get enough to drink and can no longer make it all night without urinating. She is even going in the house while we are away at work and I can tell this upsets her. Her veterinarian suspects it is Cushing's disease. What is this and can she be treated?

A: Cushing's disease, also called hyperadrenocorticism, involves an increased production of glucocorticoid hormones (the primary one being cortisol) by the adrenal glands. These hormones are needed to stimulate thirst, hunger and maintain a normal level of alertness.

They are produced by the two adrenal glands, with one sitting beside each kidney within the abdominal cavity. The production of cortisol is tightly regulated by another gland called the pituitary. This one sits just below the brain. It is constantly measuring cortisol levels and telling the adrenal glands when to make cortisol.

There are two forms of Cushing's disease, pituitary dependent and adrenal dependent. It is important to know which form a patient has as this affects treatment options, response to treatment and prognosis.

Pituitary-dependent hyperadrenocorticism is by far the most common form, with about 85 percent of cases. This is especially true for smaller-breed dogs such as your dachshund.

With this form, there is a small tumor of the pituitary gland that is constantly signaling the adrenal glands to produce cortisol. It no longer provides negative feedback to the glands when these levels are elevated.

Since the adrenal glands are being constantly stimulated, both glands may increase in size. In rare cases the pituitary tumor may enlarge. Larger pituitary tumors can place pressure on brain tissue and nerves, causing blindness, circling and seizures.

Adrenal-dependent hyperadrenocorticism is the least common of the two, accounting for 15 percent of cases.

Here, one adrenal gland has a tumor that continuously produces cortisol even though the pituitary gland is no longer signaling it to do so. The normal gland will often decrease in size. With these tumors, 50 percent are benign and 50 percent are malignant. The malignant ones can invade local structures such as the kidney or vena cava, or spread to the liver and lungs.

Symptoms of Cushing's disease have excessive thirst, increased urination, ravenous appetite, hair loss, panting, restlessness and abdominal distention. Basic blood tests may reveal increased liver enzymes.

To diagnose Cushing's disease, two tests are used: the LDDS test and the ACTH stimulation test.

The frustration is that these tests are not 100 percent accurate. A small number of dogs with Cushing's disease will have normal results and a small number of normal dogs will have abnormal results.

It is important to base the diagnosis not just on laboratory results but also on clinical symptoms.

Most veterinary endocrinologists believe the LDDS test is the more accurate test. It also may be able to differentiate the form of Cushing's disease (pituitary vs adrenal) while the ACTH stimulation cannot.

The problem with the LDDS test is that it takes eight hours to perform while the ACTH stimulation requires only one hour.

Once a diagnosis of Cushing's disease is made, the form must be determined if the LDDS test did not differentiate between the two.

The most common method is by using an ultrasound to look at the adrenal glands. With pituitary disease, both are usually symmetric while with adrenal disease one is often enlarged and irregular in shape.

Most dogs with pituitary-dependent disease respond well to medical therapy. The two most common and effective drugs are Lysodren and Trilostane.

Lysodren has been used for several decades and works by selectively destroying the adrenal gland. The goal is to destroy a portion of the gland until it produces normal levels of cortisol. Over-treating results in low cortisol levels and a disease called Addison's. If carefully monitored during therapy, this is rare.

Trilostane works by inhibiting cortisol production. Side-effects are rare but there is a small population of dogs where the Trilostane also will destroy the adrenal gland and cause Addison's disease.

If there is an adrenal tumor, it may be treated surgically or medically.

Surgical removal of a benign tumor should be curative. Malignant tumors are more difficult to cure especially if they have already spread. Some adrenal tumors will respond to medical therapy as well.

When treated and monitored closely, the quality of life for dogs with Cushing's disease can be greatly improved.

Dr. Henri Bianucci and Dr. Perry Jameson are with Veterinary Specialty Care LLC. Send questions to petdocs@postandcourier.com.