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Addison’s Disease (Hypoadrenocorticism)

Addison’s disease, or hypoadrenocorticism, is a hormonal disorder found mostly in dogs. It has been seen in cats but only extremely rarely. The disease is caused by the abnormal production of cortisol or aldosterone, or both. Cortisol and aldosterone are normally produced by the adrenal glands. If these glands are diseased or damaged the level of hormone required for healthy function is no longer produced. The pituitary gland — another hormone producing gland, located close to the brain — can also influence the adrenals. If the pituitary gland is not functioning correctly this can also cause a decrease in the level of cortisol and aldosterone.

Addison’s  is an uncommon to rare disease in dogs. Some breeds seem more predisposed to Addison’s, including Great Danes, Rottweilers, Poodles, West Highland white terriers and Wheaten terriers. The average age at which dogs are affected is about four years old, but Addison’s can strike dogs as young as a year old, as well as older pets, up to to twelve years of age. Female dogs seem to be at higher risk than males.

Clinical symptoms

The signs are variable and, particularly in patients with the chronic form of the disease, may be limited. In dogs suffering an acute Addisonian crisis symptoms may be severe and life threatening.

Some of the signs seen in dogs presenting with Addison’s are lethargy and weakness, loss of appetite, vomiting, weight loss, diarrhoea, shaking, increased thirst and increased urination. Symptoms such as these can very easily be confused with non-specific diseases, particularly gastrointestinal disease or kidney disease. It’s very important that dogs showing these symptoms be examined by a vet to establish the true cause.

How is it diagnosed?

A general blood test will alert us that all is not right. It is common to see electrolyte disturbances, and sometimes anaemia (low red blood cell count) or even liver enzyme elevation. A blood test will usually also reveal disturbances with kidney function.

Although these results are indicative of Addison’s they do not provide confirmation and we will usually run a second test — an ACTH stimulation — to definitively confirm the presence of the disease. An ACTH stimulation test involves taking a second blood test, then injecting the patient with a hormone called ACTH, designed to stimulate the adrenals to produce cortisone. A follow-up blood test is taken an hour later to measure how much the cortisone levels have increased in the blood stream. If they have not increased at all it suggests that the adrenal glands are not working and your pet has Addison’s disease.

Treatment protocols

An animal confirmed to have Addison’s disease will need to be placed on life long hormone replacement medication, and may need increased doses during periods of stress such as travel, hospitalisation and surgery. We will usually need to take weekly baseline blood tests until their hormones are stabilised. To check their electrolytes and kidney function they will then need a blood test once a month for the first 3-6 months, then a routine blood test every 3-12 months.

Unless Addison’s has been caused by a pituitary or adrenal cancer, the vast majority of patients with hypoadrenocorticism have a good to excellent prognosis following proper stabilisation and treatment. With proper care most Addison’s sufferers will continue to live active and healthy lives.

Note: Hypoadrenocorticism (Addison’s disease) should not be confused with hyperadrenocorticism, or Cushing’s disease.