Dog: Addison’s Disease
Addison’s disease is a condition in which the dog’s adrenal glands do not produce enough corticosteroids (cortisol) and/or mineralocorticoids (aldosterone).
The adrenal glands are small organs located next to the kidneys. The inner portion of the gland is called the medulla and the outer area is called the cortex. While both layers produce different types of hormones, Addison’s disease involves the hormones produced in the cortex-cortisol and aldosterone.
Cortisol helps a dog adapt to stress. It is involved in the metabolism of carbohydrates, fat and protein into energy and manages the immune system’s inflammatory response. Production of cortisol is controlled by the pituitary gland located at the base of the brain. The pituitary gland produces adrenocorticotropic hormone (ACTH) which stimulates the adrenal cortex to produce cortisol. The hypothalamus secretes corticotrophin releasing hormone (CRH) which in turn stimulates the pituitary gland to produce ACTH. Aldosterone helps to regulate blood pressure, electrolytes and water balance. The production of aldosterone is only minimally controlled by the brain.
There are two classifications of Addison’s disease:
- Primary Addison's
- Secondary Addison's
In primary Addison’s, the adrenal insufficiency is due to damage to the adrenal cortex. Clinical signs are not seen until over 85% of the cortex is destroyed. This form is most commonly seen in dogs. Both cortisol and aldosterone levels are decreased in the primary form. Primary Addison’s is caused by:
Secondary Addison’s is caused by improper transmission of ACTH from the pituitary or reduced production of CRH by the hypothalamus. Because of this, the adrenals do not receive the signal to produce cortisol. Since aldosterone production is not controlled by the brain and the adrenal gland is functioning properly, only cortisol levels are diminished in the secondary form. Secondary Addison’s is caused by:
- Damage to the pituitary gland or the hypothalamus from trauma or inflammation.
- Tumors of the pituitary gland.
- Long-term cortisone type medications in oral, injectable or ointment forms will elevate the blood cortisol levels. This sends a negative signal to the brain that the body has enough cortisol. Consequently, the brain decreases production of CRH and ACTH which prompts the adrenal glands to shut down production of cortisol. If the medication is stopped suddenly, the adrenal glands cannot produce enough cortisol to maintain physiologic levels.
Addison’s disease usually affects young dogs (4-5 years) with females afflicted twice as often as males. Clinical signs of Addison’s disease are vague and can mimic many other disease conditions. Weakness, listlessness and depression are common. Loss of appetite with vomiting and diarrhea can also occur. In severe cases, an Addisonian crisis can trigger cardiac dysfunction, shock and possibly death.
Diagnosis can be difficult and is based on clinical signs and the results of a complete blood count (CBC) and serum biochemistry tests. Blood tests may show electrolyte abnormalities with low blood levels of sodium and chloride and elevated blood levels of potassium and calcium. Hypoglycemia (low blood sugar) may occur. An ACTH stimulation test can be performed to diagnose Addison’s. This test measures the ability of the adrenal glands to produce cortisol.
Hospitalization is usually required in treating Addison’s disease. Dogs in shock will need intravenous fluids and treatment for high potassium levels. Replacement of cortisol levels with intravenous corticosteroids is necessary. Once stabilized, some dogs will need life-long medication to provide mineralocorticoid (aldosterone) replacement. Electrolyte levels will need to be monitored regularly.
If Addison’s disease is diagnosed promptly and treatment instituted, the prognosis is good for a recovery. Owners need to follow the recommended therapeutic plan made by their veterinarian.
Pituitary tumors carry a poor prognosis.
Dog’s with Addison’s may be more prone to an Addisonian crisis in times of stress and excitement. This is an emergency condition and should be treated by a veterinarian immediately.
Update version: 4/24/2014, © Copyright by www.enpevet.de
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