Also known as hypoadrenocorticism, Addison’s disease is an endocrine disorder caused by a deficiency of corticosteroids (adrenal insufficiency) which are produced by the adrenal glands. The cause is the destruction of the adrenal cortices, which are responsible for producing a number of hormones.
What is the adrenal gland?
Located on top of the kidneys, the adrenal cortices (also known as suprarenal glands) have an outer and inner layer.
- Adrenal cortex: The outer layer of the gland, called the adrenal cortex, produces hormones including cortisol, DHEA, estrogen, and testosterone. Cortisol is essential for life, it plays several important roles, some of which include converting proteins into energy, releasing glycogen and has pronounced anti-inflammatory and immunosuppressive effects.
- Medulla: The inner portion of the adrenal gland which produces epinephrine and norepinephrine (adrenaline). During a stress response, adrenaline raises blood glucose levels, blood pressure, and cardiac output.
The most common cause of Addison’s disease is the destruction of the adrenal gland cells by the cat’s own immune system. Other causes may include cancer and long-term glucocorticoid withdrawal, trauma, infection and internal bleeding.
Symptoms often reflect electrolyte imbalances caused by the disease. Hyponatremia and hyperkalemia are the two major electrolyte abnormalities of primary adrenal insufficiency.
Hyponatremia (low blood sodium levels): occurs in cats with Addison’s disease due to by increased release of antidiuretic hormone (ADH) which results in water retention and a reduction in the plasma sodium concentration. Sodium is responsible for muscle and nerve function.
Hyperkalemia (high blood potassium levels): A major function of aldosterone is to increase urinary potassium secretion, decreased levels of aldosterone lead to a build up of potassium in the blood.
- Loss of appetite
- Irregular heartbeat
- Weight loss
- Episodic vomiting
- Weight loss
- Increased thirst and urination
- Sudden collapse
Without treatment, a life-threatening Addisonian crisis (or adrenal crisis) may occur, where the cat collapses in a state of shock. This is a medical emergency and requires immediate veterinary treatment.
Addison’s disease has many symptoms similar to other disorders so diagnosis can sometimes be difficult. Your veterinarian will perform a physical examination and obtain a medical history from you. The exam may reveal a slow pulse, irregular heartbeat and signs of dehydration.
- Complete blood count which may reveal anemia as cortisol is required for red blood cell production and elevated eosinophils, a type of white blood cell.
- Biochemistry profile may show elevated potassium and phosphorous levels, low sodium and blood sugar levels and elevated liver enzymes.
- Urinalysis which commonly shows mild to severe dehydration.
- ACTH stimulation test: This test measures the ability of the adrenal glands to respond to a hormone known as adrenocorticotropic hormone (ACTH). Produced in the pituitary gland, ACTH travels through the bloodstream to the adrenal glands where it stimulates the secretion of other hormones such as hydrocortisone from the cortex. The ACTH stimulation test measures levels of cortisol in the blood before and after an injection of synthetic ACTH.
- Abdominal radiographs or ultrasound may show smaller than normal adrenal glands.
- Treatment is lifelong administration of the deficient adrenal hormones (corticosteroid and mineralocorticoid). Electrolytes will be closely monitored initially and where necessary, adjust the dosage.
- Sodium (salt) added to the diet.
- Intravenous fluid therapy to correct dehydration and electrolyte imbalances.
- Medication to replace deficient steroids.
 The Cornell Book of Cats.