Addison's disease in dogs is also known as hypoadrenocorticism. It is a disease that results from the reduction in corticosteroid secretion from the adrenal gland. The adrenal gland is a small gland located near the kidney that secretes several different substances that help regulate normal body functions.

When the adrenal glands do not function adequately, life critical hormones such as cortisol and aldosterone are not produced at sufficient levels.  The dog’s metabolism and electrolyte imbalance cause the clinical signs seen in Addison's disease.

Causes

There are several different reasons the adrenal glands may fail. By far, the most common is destruction of the glands by the body’s own immune system. Other causes can be infections in the adrenal gland, infarcts and tumours. Another cause of Addison's can be the failure of the pituitary gland (in the brain) which sends a chemical message to the adrenal gland prompting it to keep functioning.. Failure of the pituitary gland to send this message usually a result of a tumour, inflammation, or injury of this gland.

Clinical signs

Addison's is primarily a disease of young to middle-aged female dogs, however, a dog of any age and either sex can develop the disease. It does not appear to be more common in any one particular breed. Cats can develop this disease, but it is extremely rare. The symptoms of Addison's disease are very vague and many animals may have symptoms for a long time before the disease is diagnosed. Some of the more common symptoms include lethargy, anorexia, vomiting, and muscle weakness. The symptoms may wax and wane, further complicating the diagnosis. The other presentation for this disease is an episode called an 'Addisonian crisis.' In this scenario, the animal collapses in a state of shock due to an imbalance of electrolytes and metabolism during a period of stress. This episode may be the first time the owner suspects disease and may be fatal, if not treated promptly.

Diagnosis

Diagnosis is of Addison's disease in dogs is confirmed by a blood test called the ACTH stimulation test. However, because the disease is not very common and has a wide variety of symptoms, the ACTH test is usually done after several other tests are used to rule out more common diseases.

If the animal comes into the hospital in an Addisonian crisis with electrolyte imbalances, and responds to therapy, then a presumptive diagnosis of Addison's disease is made and once the animal recovers, the diagnosis can be confirmed with an ACTH stimulation test.

If however, the animal presents with a history of weight loss, lethargy, or muscle weakness, which are the symptoms of many diseases, a chemistry profile and blood count are usually performed first to look at a number of body systems. Dogs with Addison's disease often have elevated blood urea nitrogen (BUN) and an elevated creatinine, as well as decreased blood glucose. The blood count may show a chronic anaemia. If the blood work supports the diagnosis of Addison's diseases, then an ACTH challenge test is performed.

In an ACTH challenge test, the dog is given an injection of the adrenal stimulating hormone ACTH. A normal dog will respond by having an increase in blood cortisol. If a dog with Addison's disease is given ACTH, the dog will not have an increase in blood cortisol and the diagnosis of Addison's disease is confirmed.

Treatment

Once the disease is diagnosed, the treatment is fairly straightforward. The standard treatment involves replacing the mineralocorticoids and glucocorticoids in the body. The drugs most commonly used to accomplish this are Florinef (fludrocortisone). Florinef is usually given twice a day. Initially, the blood sodium and potassium levels are monitored to help obtain the correct dose. After the animal is regulated, then the levels are rechecked 2 to 3 times a year and adjustments in dosing are made as needed.

A newer option in the treatment of Addison's disease is a drug called DOCP. The injection is long acting and only needs to be given once every 25 days. DOCP has been intensively tested and been shown to provide better electrolyte regulation than Florinef. Some animals on DOCP may also need to be placed on a low maintenance dose of prednisone.

Living and Management

If your dog is being treated with medications for this condition, you will need to be prepared to continue treatment for the life of your dog. You will need to be observant of any side effects to medications. Signs of an adverse side effects include lack of energy, weakness, lack of appetite, vomiting, diarrhoea, and possible difficulty walking. If any of these side effects do occur, you should discontinue the medication, and administer Prednisone (which will be dispensed to you for your dog) as per instructions, and contact us immediately.

Once your dog has its Addison’s disease stabilised, you pet will need appointments and blood tests at the one, three, and six months mark, then annually after that.