TREATMENT OF HYPOANDRENOCORTICISM

Hypoadrenocorticism or Addison’s disease

WHAT ARE THE ADRENAL GLANDS?
The adrenal glands are two small bean-shaped organs less than 1cm in height and width that are located next to each kidney in the abdomen. They produce several hormones, two of which are crucial for survival. These are glucocorticoids (cortisol) and mineralocorticoids (aldosterone). Glucocorticoids have many functions in ensuring you feel well. Cortisol is important for responding to stress. It also helps stimulate appetite, affects immune function and maintains a normal blood glucose. The main mineralocorticoid, aldosterone, is important for salt (electrolyte) concentrations in the body fluids, specifically sodium and potassium. Too much or too little of either glucocorticoids or mineralocorticoids causes serious medical problems.

WHAT IS HYPOADRENOCORTICISM?
Hypoadrenocorticism, also known as Addison’s disease, is sometimes called the great pretender as it can imitate all sorts of other diseases and therefore can be challenging to diagnose. This disease occurs when the adrenal glands produce too little of these important hormones (cortisol and aldosterone). In dogs and cats, it most often occurs when the body's own immune system attacks cells of the adrenal gland. The function of the immune system is normally to protect the body against foreign substances and organisms. In immune mediated disease the cells of the immune system cannot recognise 'self' from 'foreign’ and start attacking cells from the individual's own body.

CLINICAL SIGNS

WHAT ARE THE SYMPTOMS OF HYPOADRENOCORTICISM?
Hypoadrenocorticism is uncommon in dogs and rare in cats. Dogs most often affected are young to middle-aged of any breed, however in some breeds it may be hereditary (Standard Poodle, Bearded Collie). Animals that have hypoadrenocorticism commonly lose their appetite, have vomiting or diarrhoea and they become lethargic and weak. Animals may have chronic waxing and waning clinical signs over a period of months or may present in a crisis, critically unwell and in shock.

DIAGNOSIS, PROCEDURES AND TREATMENT

WHAT TESTS ARE NEEDED?
Because the symptoms are not specific for hypoadrenocorticism, and it is an uncommon disease, often a number of tests will need to be done to diagnose hypoadrenocorticism. It tends to mimic several other diseases such as kidney, liver and gastrointestinal disease. Blood work and abdominal imaging such as radiographs or ultrasound may be performed. Classic abnormalities that may be found on a blood biochemistry test are low sodium and high potassium. Some animals may also have low glucose, high calcium, elevated kidney values and anaemia. These changes are suggestive but not specific to hypoadrenocorticism. To definitively diagnose hypoadrenocorticism, another test called an ACTH stimulation test needs to be performed. If the results of this test are typical for hypoadrenocorticism then the diagnosis is made. Some medications interfere with this test such as prednisolone tablets or topical steroid preparations, medications used to lower cortisol levels (such as trilostane), and some antifungals and anti-testosterone drugs. It is important to make sure your vet knows all the medications your pet has been treated with when trying to make a diagnosis of hypoadrenocorticism.

WHAT TREATMENTS ARE AVAILABLE?
When pets are first seen by the vet for hypoadrenocorticism, they could be in a critical state and may need intensive care. Intravenous fluids and other medications to rapidly lower the potassium may be required to be given through a drip. Treatment of high potassium is critical as it can cause changes to the heart rhythm and even cardiac arrest. Your pet may require constant ECG monitoring until electrolytes are improved. The sodium needs to be slowly increased as rapid changes of this electrolyte can cause neurological problems. Several blood tests to check the level of electrolytes during this intensive phase of treatment are needed. Rarely dogs may also require a blood transfusion as bleeding into the intestines can occur after a crisis.

Not all animals are critically ill when diagnosed. Some animals who are stable enough will not require intensive therapy and can be managed as out-patients.

However, all animals diagnosed with hypoadrenocorticism will require lifelong medication to replace the hormones they can no longer produce. Two methods of treatment exist: which one is chosen depends on what suits you and your pet the best.

Fludrocortisone tablets (Florinef) - these tablets contain both glucocorticoids and mineralocorticoids. Some animals also need extra glucocorticoids (prednisolone or cortate). Tablets are given once to twice daily.
Injections of Desoxycorticosterone pivalate (Percorten or Zycortal) injection once every 25 to 30 days. The medication in this injection only replaces mineralocorticoids, so your pet will also need to take a tablet daily to replace glucorticoids (prednisolone).

Often pets can do well on either medication regime, but there may be times when a change to different medications is recommended. In pets where we are having difficulty controlling their electrolytes on Florinef or they are drinking excessively, the DOCP injections may be a better choice. For both regimes, blood tests are usually required weekly until the electrolytes are stabilised. then periodic monitoring is required approximately every 3 to 6months for the rest of the animal’s life.