vp_cushing_dog_diagram_cms_resizeto_320x320.202411 - Caption. [Optional]

What is Hypoadrenocorticism? 

The adrenal glands are small, paired glands next to the kidneys that produce several hormones that regulate a variety of body functions necessary to sustain life. Hypoadrenocorticism (previously called Addison’s disease) is characterized by reduced to absent adrenal gland function.

Cortisol, commonly called cortisone or simply “steroid,” is the most widely known hormone. It is needed by every cell in the body and is essential to protein, fat, and carbohydrate metabolism and maintaining a healthy intestinal tract. The term steroid is confusing as it can be used to describe other compounds that can be taken to build muscle.

The adrenal glands also produce another hormone called aldosterone, which regulates sodium, potassium, and water balance. Patients with aldosterone deficiency can become dehydrated and develop low sodium concentrations, high potassium concentrations, and/or low blood pressure.  A patient that doesn’t produce enough cortisol and, especially, aldosterone will become unwell.  Hypoadrenocorticism can be life-threatening.

Different Types of Hypoadrenocorticism

Dogs can be deficient in cortisol and aldosterone. Gastrointestinal signs are usually present, along with low sodium (hyponatremia) and high potassium (hyperkalemia). This form has previously been called typical Addison’s disease. Currently, the preferred term is hyponatremic, hyperkalemic hypoadrenocorticism. 

The other form occurs when only cortisol is deficient. Because aldosterone is unaffected, sodium and potassium remain normal. It is called eunatremic, eukalemic hypoadrenocorticism (previously called atypical Addison’s disease).

What Causes Hypoadrenocorticism?

A little physiology is needed to understand the causes of hypoadrenocorticism.

The pituitary gland, which is part of the brain, controls cortisol secretion. If the pituitary gland is not functioning, cortisol secretion from the adrenal glands stops. Therefore, damage to the pituitary or the adrenals can cause cortisol deficiency. Aldosterone deficiency is caused only by damage to the adrenals, not to the pituitary. 

Often, the cause of the pituitary no longer functioning is not known. Possible causes are destruction by a tumor or head trauma. The most common cause of adrenal gland destruction is when the patient’s own immune system attacks and destroys the adrenal glands, i.e., autoimmune disease. 

Other possible causes are destruction of the adrenal glands by tumor or infection or the use of certain drugs, e.g., trilostane (Vetoryl) or mitotane. The cause may not be known in any particular case. Also, the administration of drugs like hydrocortisone, prednisone, or dexamethasone can temporarily cause the adrenals to stop secreting cortisol. 

If hypoadrenocorticism occurs due to drug administration, it may be temporary. In all other cases, it will be permanent and require lifelong care.

Clinical Signs of Hypoadrenocorticism

Clinical signs can be acute and life-threatening or chronic, vague, and not very specific. Signs often involve the gastrointestinal tract: depression, vomiting, weight loss, and diarrhea, which can be bloody.  Increased thirst and urination can also occur. These signs may come and go, and often, your pet will improve with non-specific, symptomatic, and supportive care. If your dog experiences recurrent lethargy, diarrhea, vomiting, and increased thirst/urination, hypoadrenocorticism should be considered.

In summary, the common signs of hypoadrenocorticism are:

• Loss of appetite
• Lethargy
• Weakness
• Vomiting
• Diarrhea
• Weight loss
• Shivering, tremors, muscle stiffness
• Depression
• Dehydration

Since these signs are seen in many other diseases, diagnosis may not be straightforward. Hypoadrenocorticism is called “the great pretender” because it looks like so many other diseases.

Diagnosing

Hypoadrenocorticism is usually suspected based on a dog’s age, breed, and clinical signs. This is a disease of younger to middle-aged dogs. Common dog breeds with hypoadrenocorticism include:

• Standard Poodles,
• Labradoodle,
• Goldendoodle,
• Portuguese Water Dogs,
• Nova Scotia Duck Tolling Retrievers, and
• Bearded Collies.

Your veterinarian will perform a thorough physical examination and a series of blood tests to help confirm the diagnosis. One way to rule out hypoadrenocorticism is to measure a single cortisol concentration. If the concentration is high enough, a diagnosis of hypoadrenocorticism can be eliminated in a relatively inexpensive way. If the cortisol is not high enough to rule out hypoadrenocorticism, an ACTH stimulation test is needed. This test requires injecting the hormone ACTH and two or three blood samples taken over one to two hours. Additional tests, such as X-rays or abdominal ultrasound, may be performed to help exclude other causes of your pet’s clinical signs.

Treatment and Quality of Life

Once diagnosed, most dogs can be successfully treated with oral and/or injectable medications, and they resume normal lives.

In the beginning, all patients with hypoadrenocorticism are put on therapy to replace cortisol, i.e., daily oral prednisone, prednisolone, methylprednisolone, or hydrocortisone. Doses can be altered to make sure the clinical signs of hypoadrenocorticism have resolved and to minimize the side effects of the medication, the most common of which is excess drinking and urination. 

Aldosterone can be replaced either with daily oral medication (Florinef® or fludrocortisone, given twice daily; hereafter called just “Florinef®”), or with a monthly injection of Percorten®or Zycortal®. The effectiveness of these three drugs is determined by the normalization of blood sodium and potassium concentrations. 

The starting dose of Florinef® is often lower than most dogs need, and the dose is increased to normalize sodium and potassium. On the contrary, the dose of Percorten® and Zycortal® is often more than most dogs need, and the dose is decreased until the lowest dose needed is determined.

Generally, veterinarians believe that Percorten® and Zycortal® are better options than Florinef®. In some dogs, despite continued dose increases, sodium and potassium concentrations never become normal on Florinef®. In addition, Florinef® has some cortisol-like activity, so it can cause the same side effects as prednisone.  

When a dog responds well to Florinef®, concurrent prednisone, prednisolone, methylprednisolone, or hydrocortisone can be weaned down or off. However, a dog receiving Percorten® or Zycortal® as aldosterone replacement will always require daily prednisone, prednisolone, methylprednisolone, or hydrocortisone in addition to those injections.

The body normally secretes excess cortisol during times of stress. Since patients with hypoadrenocorticism can’t secrete cortisol to help with stress, prednisone, prednisolone, methylprednisolone, or hydrocortisone doses need to be increased during these times. “Stress” can be anything from boarding to surgery and illness. If a dog is on Florinef® and not on daily prednisone, prednisolone, methylprednisolone, or hydrocortisone, one of these medications should be given during the period of stress. 

In addition, it is a good idea that your veterinarian evaluates your dog every six months to ensure appropriate stabilization and management of the disease. Performance of a complete blood count, serum biochemistry, and urinalysis is recommended.