Diseases of the Adrenal Glands

What do a dog’s adrenal glands do?

A dog has two adrenal glands, which are located in the abdomen just in front of each of the kidneys. The adrenal glands produce crucial hormones that regulate vital bodily functions like metabolism, blood pressure and stress response. They are essential for maintaining overall health and well-being.

The adrenal gland has two parts — the cortex and the medulla.

The adrenal cortex is subdivided into three layers, and each layer produces a different set of steroid hormones. The outer layer produces the mineralocorticoids, which help to control the body’s balance of sodium and potassium salts. The middle layer produces glucocorticoids, which are involved in metabolizing nutrients, breaking down fats and proteins, as well as reducing inflammation and immune responses. The inner layer produces sex hormones such as estrogen, progesterone and androgens, which impact reproductive functions.

The adrenal medulla plays an important role in response to stress or low blood sugar. It releases epinephrine, also called adrenaline, and norepinephrine, both of which increase heart output, blood pressure and blood sugar. These also act to slow digestion. Epinephrine/adrenaline is the “fight or flight” hormone that is crucial for short-term stress reactions.

What happens when the adrenal glands produce too many hormones?

Dogs can struggle if the adrenal glands overproduce glucocorticoids, or cortisol. This is called hyperadrenocorticism, also known as Cushing’s disease. There are three types of Cushing’s disease, each with a different cause. Identifying the cause is important because each type is treated differently, and each has a different prognosis.

The most common cause of Cushing’s disease (approximately 85 to 90 percent of all cases) is a tumor of the pituitary gland, which is located at the base of the brain. The tumor may be either benign (harmless) or malignant (cancerous). The tumor causes the pituitary gland to overproduce the hormone ACTH, which stimulates the adrenal glands to produce cortisol.

Pituitary tumors may be large or microscopic. If the activity of the adrenal gland can be controlled with medication, many dogs with this form of Cushing’s disease can live normal lives for many years. If the pituitary tumor grows, it will affect the brain, often resulting in neurological signs and a less favorable predicted outcome.

Adrenal-gland tumors are another cause of Cushing’s disease. If the tumor is benign, surgical removal will cure the disease. If the tumor is malignant, surgery may help for a while, but the prognosis is much more guarded.

The third type of the disease is iatrogenic Cushing’s disease. It occurs when there is excessive use of an oral or injectable steroid medication. Although steroids are helpful in treating certain medical conditions, in this case, their excess has become harmful to the patient.

What are the signs of Cushing’s disease?

Regardless of the type, the clinical signs of Cushing’s disease are the same. The most common signs are increased appetite, water consumption and urination. The increased appetite is a direct result of elevated cortisol levels, which stimulate the appetite. Lethargy and a poor hair coat are also common signs.

Many “Cushingoid” dogs develop a bloated or pot-bellied appearance because of an increase of fat within the abdominal organs. This stretches the abdominal wall as the organs get heavier and the muscles of the abdominal wall get weaker. Other signs include panting, chronic skin infections, skin mineralization called calcinosis cutis, and persistent bladder infections.

How is Cushing’s disease diagnosed?

The two most common blood tests to detect Cushing’s disease are the ACTH stimulation test and the low-dose dexamethasone suppression (LDDS) test. Other tests that may help determine the type of the disease are the levels of the hormone ACTH in the body, a high-dose dexamethasone suppression (HDDS) test, or a urine cortisol/creatine ratio. Although these tests can be expensive, they are necessary to determine the best treatment and prognosis for your dog.

What are the treatment options for Cushing’s disease?

Treatment of the pituitary-induced form of Cushing’s disease can be complicated. Trilostane (brand name Vetoryl) is the drug most prescribed. It works by blocking an enzyme involved in hormone synthesis. Mitotane (Lysodren) is another option. It destroys adrenal tissue and can be associated with more side effects. Selegilene hydrochloride (Anipryl), and ketoconazole (Nizoral) are other medications, although they are not considered as effective as trilostaine or mitotane and are not typically recommended.

Adrenal tumors are best treated by surgical removal. If the surgery is successful and the entire tumor is removed and found to be benign, there is a good chance that the dog will regain normal health. If surgery is not an option, some of these patients can be managed with medication, as discussed above, although they do not tend to respond as well. Mitotane may be more effective with adrenal tumors as it can be destructive to the tumor itself at higher doses. Radiation is an option at certain referral centers.

Iatrogenic Cushing’s disease is treated by discontinuing the steroid being given. The drug must be withdrawn in a controlled, gradual way so that other complications do not occur. Other treatment options for the primary disease must be explored.

Are there cases where the adrenal glands do not produce enough hormones?

When the adrenal glands are not producing enough hormones, the diagnosis is hypoadrenocorticism, also called Addison’s disease. Usually there is a deficiency of cortisol as well as aldosterone. Aldosterone plays a role in the regulation of fluids and electrolytes in the body. Cortisol, a stress hormone, helps regulate the body’s sugar levels and metabolism to provide fuel for the body when it is urgently needed.

If the secretion of aldosterone is decreased, the levels of potassium, sodium and chloride in the blood are affected. Potassium gradually builds up in the blood, and, in severe cases, may cause the heart to slow down or beat irregularly. Some dogs’ heart rate can slow to 50 beats per minute (normal canine heart rate is 60 to 140 bpm) or lower. These dogs become weak and may go into shock. Decreased production of cortisol results in low blood-sugar levels.

What are the symptoms of Addison’s disease?

The symptoms of Addison’s can be vague and include vomiting, diarrhea, loss of appetite, dehydration, weight loss, weakness, shivering and lethargy. Although signs can be hard to identify while Addison’s disease is developing, severe consequences, such as shock and kidney failure, can develop quickly. Some dogs may experience an “Addisonian crisis”: They collapse and have a slow heart rate with a low body temperature. This is a medical emergency.

How is Addison’s disease diagnosed?

The range of non-specific symptoms can make Addison’s disease difficult to diagnose. Although the disease can be seen in any breed, sex or age, it is most common in young adult female dogs. Bloodwork may reveal changes in the sodium and potassium levels, but a specific test called an ACTH stimulation test is required to confirm the diagnosis.

What is the treatment for Addison’s disease?

The treatment for Addison’s disease involves lifelong hormone-replacement therapy, including both glucocorticoid and mineralocorticoid supplementation, with both oral and injectable medications. Glucocorticoids are supplemented with oral medications like prednisone to replace the missing cortisol. Desoxycorticosterone pivalate (DOCP) is an injectable medication that replaces the missing mineralocorticoid hormone aldosterone. This drug’s brand name is Percortin and is given every 21 to 30 days.

Regular blood tests are important to monitor hormone and electrolyte levels for both Cushing’s and Addison’s diseases, allowing for adjustments to medication dosages as needed.