What is Addison’s disease?
Addison’s disease, also known as hypoadrenocorticism, is a condition in which the adrenal glands do not produce enough glucocorticoids (steroids) to allow normal body function.
This condition is considered rare in cats, but numerous cases have been reported. Hypoadrenocorticism is most common in middle-aged cats, though it has also been reported in younger cats. The disease appears to be equally common in males and females. There is no apparent association with breed.
What are the adrenal glands and what do they do?
The adrenal glands are small, paired glands located near the kidneys. Each gland consists of an outer cortex and an inner medulla. The glands produce two important hormones that regulate a variety of body functions and are necessary to sustain life. The two hormones are cortisol, a stress hormone, and aldosterone, a hormone that regulates the body’s levels of the minerals sodium and potassium. Sodium and potassium levels are important for maintaining the body’s fluid balance.
What causes hypoadrenocorticism?
Hypoadrenocorticism occurs when the normal adrenal gland tissue is destroyed. In most cases, this destruction occurs because of an immune reaction; the body’s immune system begins attacking the adrenal gland. Rarely, hypoadrenocorticism may be caused by an adrenal gland tumor or trauma.
What are the signs of hypoadrenocorticism in cats?
Affected cats often have a history of waxing and waning periods of lethargy, decreased appetite, and weight loss. Some cats may also have a history of vomiting episodes. Diarrhea, a common sign of hypoadrenocorticism in dogs, is rarely observed in affected cats.
On a physical examination, your veterinarian may notice dehydration, weakness, an abnormally slow heart rate, and a loss of body fat and muscle mass. Many cats present in shock, with weak pulses, severe dehydration, and extreme weakness.
How is hypoadrenocorticism diagnosed?
If your cat presents to the veterinarian with signs of hypoadrenocorticism, your veterinarian will likely begin by performing baseline lab testing, including a complete blood cell count, serum biochemistry, and urinalysis. Certain characteristic abnormalities in the bloodwork can alert your veterinarian to the likelihood of hypoadrenocorticism, although not all of these abnormalities are present in every affected cat. Common bloodwork abnormalities include changes in sodium and potassium levels and elevated kidney values. Additionally, affected cats typically have dilute urine on urinalysis.
"If your veterinarian suspects hypoadrenocorticism, he or she will recommend an ACTH stimulation test."
If your veterinarian suspects hypoadrenocorticism, he or she will recommend an ACTH (adrenocorticotropic hormone) stimulation test. This test helps distinguish hypoadrenocorticism from kidney failure, which can cause similar lab work abnormalities. An ACTH stimulation test involves taking a baseline blood sample, giving an injection of ACTH, and then taking a second blood sample one to two hours later. Cortisol levels are assessed in both samples, giving an indication of how well the body’s adrenal glands respond to ACTH stimulation. A normal cat should produce increased levels of cortisol when stimulated with ACTH. Abnormally low values indicate hypoadrenocorticism.
How is hypoadrenocorticism treated?
Treatment depends on the severity of your cat’s condition.
Some cats present in crisis, with significant dehydration and weakness. These cats typically require hospitalization for intravenous fluid therapy and the administration of electrolytes. Some cats may also require immediate steroid treatment, though it is best to postpone steroids until after the ACTH stimulation test has been performed, if possible.
"Some cats present in crisis, with significant dehydration and weakness."
Long-term, cats with hypoadrenocorticism require medications to supplement the substances released from the adrenal glands. Cats typically receive two medications – one to supplement glucocorticoids (steroids) and another to supplement mineralocorticoids (which regulate electrolytes). Either of these medications can be given as daily oral tablets or as a long-acting injection. These medications will need to be continued for the remainder of the cat’s life.
Will my cat need additional care and monitoring once diagnosed with hypoadrenocorticism?
Cats with hypoadrenocorticism must receive regular veterinary care and monitoring for the remainder of their life. Your cat will likely see your veterinarian for follow-up blood tests at least once per month in the early stages of regulating the disease; this frequency will decrease over time if your cat responds well to treatment.
What is the prognosis for feline hypoadrenocorticism?
In general, the prognosis for cats with hypoadrenocorticism is good. If your cat can be successfully treated during the initial crisis and started on appropriate long-term therapy, she should go on to have a normal life expectancy.
Cases associated with adrenal tumors carry a poor prognosis. Fortunately, these cases are very rare.