Cushings and Addison's Disease

The body contains two very small glands adjacent to the kidneys known as adrenal glands. They produce a number of regulatory hormones involved in maintaining the body including cortisone and the mineralocorticoids.


Cortisone (a glucocorticoid) is a hormone involved in every day regulation of stress as well as reducing inflammation and helping in regulating the immune system. Small quantities are essential for survival but as with most hormones under or overproduction causes the body's normal status (homeostasis) to degenerate.
Cushing's Disease is also known as hyperadrenocorticism. The disease is an excess of cortisone hormone released by the adrenal glands and produces a number of problems. Several symptoms may be seen, initially excessive drinking and urination and often increased appetite to the point of thieving and eating silly things. The dog will develop a poor thin hair coat, thin skin and a pot belly as fat is laid down in the lower abdomen instead of being evenly distributed. Untreated Cushing's Disease leads to infection in the skin and sometimes calcium plaques in its surface which may crack.


Cushing's can result from excess stimulation from the Pituitary Gland in the brain (part of the normal pathway of production which can go wrong) and enlargement of the adrenal glands themselves.
Treatment of Cushing's involves a drug known as trilostane which blocks release of cortisone from the kidneys. Regular blood tests are required to ensure not all the cortisone is blocked and homeostasis is maintained. The treatment is for life and unfortunately can be expensive, however the owner should see an improvement over time in the dogs drinking, eating and hair coat even bringing some dogs back to normal which is rewarding.
Lack of adrenal output (or over suppression of Cushing's) can lead to Addison's Disease. Thus surgery to remove excess gland tissue is dangerous as it may stop production all together, drug regulation is far safer.
Addison's Disease is mainly a reduction in the mineralocorticoids but can be cortisone as well. Addison's results in a life threatening breakdown in homeostasis which can be rapidly fatal if untreated. Early signs of Addison's are vague and include diarrhoea, vomiting, lethargy, nervousness and behavioural changes in a previously confident dog. Mineralocorticoids control sodium and potassium balance in the body, two elements known as electrolytes involved in many of the cell activities of the body. The balance between these two has to be maintained within strict limits or the body cannot survive.


Treatment of Addison's mainly involves using a drug called fludrocortisone and blood tests to check electrolyte levels although some dogs need a little cortisone and salt in their diet as well.
Nobody really knows why Cushing's or Addison's occurs naturally. Both can be induced by the use of cortisone for therapy. Iatrogenic (caused by medical treatment) Cushing's is relatively common as cortisone and it's derivatives are used quite frequently for medical therapy. Withdrawing the drug results in resolution of symptoms but there may be a balance required with the disease under treatment. Too rapid a removal of cortisone can cause Iatrogenic Addison's as the medication has often suppressed the body's own hormone release including mineralocorticoids so these drugs are usually withdrawn by slowly stepping down the dose.