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Also known as 'hypoadrenocorticism', Addison's Disease is an endocrine disorder caused by a deficiency of corticosteroids which are produced by the adrenal glands. It is more commonly found in dogs and is in fact extremely rare in cats. It is generally caused by the destruction of the adrenal cortices, resulting in hormonal deficiencies.
These glands (also known as suprarenal glands) are located atop the kidneys. The gland has an outer and an inner layer.
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.
The inner portion of the adrenal gland is called the medulla and it produces epinephrine and norepinephrine (adrenaline), which during a stress response, 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.
- Anorexia (loss of appetite)
- Arrhythmias (irregular heart beat)
- Gastrointestinal disturbances (vomiting and diarrhea)
- Hypoglycemia (low blood sugar)
- Weight loss
- Hyperkalemia (high blood potassium levels)
Without treatment, a life-threatening 'Addisonian crisis' (or adrenal crisis) may occur. The cat collapses in a state of shock. This is a medical emergency.
Addison's disease has many symptoms similar to other disorders so diagnosis can sometimes be difficult. It is based on general blood work such as:
- Complete blood count
- Biochemistry profile may show elevated potassium levels and phosphorous levels and low sodium levels.
ACTH stimulation test: This test measures the ability of the adrenal glands to respond to a hormone known as adrenocorticotropic hormone (ACTH) which is made in the pituitary gland, travelling 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
- Abdominal ultrasound
Treatment is lifelong administration of the deficient adrenal hormones (corticosteroid and mineralocorticoid). Initially, electrolytes will be monitored frequently and dosage will need to be adjusted according to your cat's requirements.
Sodium (salt) may need to be added to the diet.
For Addisonian crisis your cat will require:
- Intravenous fluid therapy to correct dehydration and electrolyte imbalances.
- Medication to replace deficient steroids.
 The Cornell Book of Cats.