Addison’s Disease in Cats

About

Also known as hypoadrenocorticism, Addison’s disease is an endocrine disorder, characterised by inadequate production of the steroid hormones cortisol and aldosterone,  due to the destruction of the outer layers of the adrenal gland.

What is the adrenal gland?

The adrenal glands (also known as suprarenal glands) are two triangular-shaped glands located above the kidneys and are responsible for the production of a number of important hormones. Each gland has an outer adrenal cortex and an inner medulla.

1. 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.
2. Medulla: 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 believed to be due to immune-mediated destruction of the adrenal gland cells. Less common causes include cancer and long-term glucocorticoid withdrawal, trauma, infection and internal bleeding.

There is no breed or sex predilection.

Clinical signs

Symptoms often reflect electrolyte imbalances caused by the disease and may wax and wane. Hyponatremia (low blood sodium levels) and hyperkalemia (high blood potassium levels) are the two major electrolyte abnormalities of primary adrenal insufficiency.

Hyponatremia: 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: 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.

• Inappetence
• Irregular heartbeat
• Dehydration
• Weight loss
• Depression
• Episodic vomiting
• Lethargy
• Shaking/listlessness
• Weight loss
• Increased thirst and urination
• Sudden collapse

Without treatment,  Addisonian crisis (also known as adrenal crisis or acute adrenal insufficiency) can occur, where the cat collapses in a state of shock due to an acute deficiency of the hormone cortisol. This condition has a high mortality rate and is a medical emergency requiring immediate veterinary treatment.

Diagnosis

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.

Diagnostic workup:

• Complete blood count: May reveal anemia as cortisol is required for red blood cell production and elevated eosinophils, a type of white blood cell.
• Biochemistry profile: Elevated potassium and phosphorous, low sodium and blood sugar, and elevated liver enzymes.
• Urinalysis: May reveal mild to severe dehydration.
• ACTH stimulation test: A measure of 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:  To assess the adrenal glands, which will appear smaller.

Treatment

• 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.

Addisonian crisis:

An Addisonian crisis requires immediate veterinary attention.

• Intravenous fluid therapy to correct dehydration and electrolyte imbalances.
• Medication to replace deficient steroids.

References:

[1] The Cornell Book of Cats.