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Canine Addison's Disease (Hypoadrenocorticisim)

The adrenal glands are essential for life. They are two small glands which sit next to the kidneys. Their size does not correlate with their importance. They secrete a number of hormones essential for normal functioning as well as survival in stressful situations. Addison’s Disease (named after it’s discoverer in 1855) means there is insufficient production of these hormones. It is also called hypoadrenocorticism. Addison’s disease can be primary: atrophy (dying off) of the adrenal gland or secondary: a problem with the pituitary gland which secretes hormones that control growth and activity of the adrenal glands

Causes of Canine Addison's

Primary: It is believed that most cases of primary Addison’s Disease are due to the body’s immune system destroying the adrenal tissue. The reasons for this are unknown. Other less common causes include infections, cancer, trauma, drug side effects and various types of inflammation.

Secondary: This is due to problems with the pituitary gland which include inflammation, trauma or tumours

Physiology

The hormones produce by the adrenals can be grouped as follows:
  1. Mineralocorticoids - aldosterone
  2. Glucocorticoids - cortisol
  3. Primary Sex Hormones - androgens, oestrogens
  4. Stress Hormones - adrenalin (note: the production of these hormones seems to be unaffected in primary Addison’s Disease)

The main groups we are concerned with are the mineralocorticoids and the glucocorticoids.

The areas of the body that these hormones influence area as follows:
    • Mineralocorticoids: control the ability to maintain electrolyte and water balance in the body
    • Glucocorticoids: affect nearly every tissue in the body - promote a sense of well being & stimulate appetite; help control blood glucose levels; help the kidneys control water & calcium levels in the blood, help with control of red & white blood cell numbers.
    As you see, without these hormones we have a very sick animal which will not survive long without treatment

    Patient History

    Addison’s is seen mainly in middle aged female dogs. There seems to be no obvious breed prevalence. The disease usually follows a waxing and waning course and may be confused with other diseases as the clinical signs are very non-specific

    Physical signs

    The physical signs tend to relate to the lack of these important hormones. These will include:
    • weakness, depression, lethargy
    • anorexia, weight loss
    • vomiting, diarrhoea
    • excess drinking or urinating
    • slow heart rates
    • abdominal pain
    • hypothermia

    Laboratory Signs

    The laboratory signs are more useful in diagnosing Addison’s and will help to explain the physical signs, some or many of the following may be seen:
    • Increased Lymphocyte (a type of white blood cell) numbers
    • Anaemia
    • Increase serum potassium
    • Decreased serum sodium
    • Altered sodium/potassium ratio (Na:K): <27
    • Increased serum phosphorus
    • Increased serum calcium
    • Decreased blood glucose
    • Increased BUN & Creatinine (indicators of kidney function)
    • Acidosis (upset in body’s acid/base balance)
    • Low blood cortisol levels
    Xrays may also be done which may reveal a smaller than normal heart due to the reduction in volume of circulating fluid in the body as part of Addison’s disease

    If the pet is not too sick, a test called an ACTH stimulation is performed. As this test takes several hours to complete and sometimes days for results, treatment for Addison’s Disease can usually be instituted on other laboratory results.

    Treatment

    Treatment is normally in two stage:
    1. Adrenal Crisis Management;
    2.Maintenance therapy

    Adrenal Crisis Management is required when we have a very sick animal with abnormalities as those listed above. Your Vet will decide what the best course of action is to follow according to each individual case. This may involve fluid therapy and drugs to help reverse the changes. Once the animal has recovered to a normal state we can go onto Maintenance Therapy

    Maintenance Therapy is usually lifelong and involves tablets to replace the hormone that are deficient: ie glucocorticoids & mineralocorticoids. Your Vet will decide which medications are best for each case.

    Monitoring

    Careful monitoring of electrolytes is important throughout he early stages of Addison's disease management. Your Vet is likely to give you a list of dates when further blood tests will be needed. These will usually be quite frequent at first with the intervals between blood tests gradually increasing.