Metabolic & Hormonal Disorders

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• Cushing’s Disease
• Addison’s Disease

CUSHING’S DISEASE (HYPERADRENOCORTICISM)

WHAT IS CUSHING’S DISEASE?

Also known as hyperadrenocorticism, Cushing’s disease occurs due to an overactive adrenal gland. The adrenal glands secrete hormones required for various processes in the body. In this instance, over secretion of the stress hormone cortisol results in disease manifestation. Increased concentrations of cortisol may result in immune suppression, change in kidney and liver function and alterations to metabolism.

Cushing’s is more commonly identified in dogs than cats, with most dogs being over 6 years of age at the time of diagnosis. Breeds predisposed to the disease include Poodles, Boxers, Dachshunds and Terriers, but any breed of dog can be affected.

WHAT CAUSES CUSHING’S DISEASE?

Overactivity of the adrenal gland in dogs is most often caused by a very small and benign tumour in the pituitary gland – a small bean sized organ near the brain – which stimulates the adrenal glands. It can also be caused by a tumour on one of the adrenal glands themselves, but this is less common. A form of Cushing’s disease can also be induced by prolonged use of steroid medications that result in consistently high levels of cortisol in the animal.

SIGNS AND SYMPTOMS

• Increased drinking and appetite
• Increased urination
• Reduced activity (lethargy)
• Weight gain
• Excessive panting
• Thin skin or recurring skin infections
• Hair loss
• Enlarged abdomen – “pot-bellied” appearance

Below is an image of a dog with thinning hair and a “pot-belly”.

DIAGNOSIS

Cushing’s Disease may initially be suspected by a veterinarian when an owner reports various behavioural changes in their animal. As listed above, these could include increased panting, drinking and urinating, or decreased activity. Changes in a dog may also be physical, such as hair loss, or recurring skin infections.

Screening blood tests are often performed to check for liver enzyme increases. This, along with any physical signs increases suspicion of Cushing’s disease. Further blood tests can be performed to confirm the presence of Cushing’s. The two major options for blood tests are an ACTH stimulation test or a low dose dexamethasone suppression test. The veterinarian can determine which test would be most suitable for the patient.

TREATMENT

If Cushing’s is caused by prolonged steroid medication, a weaning plan can be established with the veterinarian to slowly take the dog off this medication. More commonly though, a pituitary tumour is the cause of Cushing’s and due to its location, removal is not attempted. Therefore, medication is the typical treatment for Cushing’s disease. Common medications used include trilostane or mitotane which reduce the production of cortisol by the adrenal glands. Both medications are given orally.

Follow up blood tests are recommended in the first few months of treatment commencing to monitor the cortisol levels in the blood. This will help with confirming the medication is being given at the right dose for the desired effect. With ongoing treatment, ongoing monitoring is absolutely necessary. This involves blood tests every few months to assess the cortisol levels in the patient.

Below are images of three different dogs with Cushing’s Disease, showing each dog at initial presentation, after 3 months of treatment, and after 6 months of treatment.

ADDISON’S DISEASE (HYPOADRENOCORTICISM)

WHAT IS ADDISON’S DISEASE?

Also known as hypoadrenocorticism, Addison’s disease occurs when there is a decrease and failure of production of one or more hormones from the adrenal glands. The two main hormone types secreted by the adrenal glands are glucocorticoids (cortisol) and mineralocorticoids (aldosterone).

Glucocorticoids are responsible for regulating blood pressure, immune system function, energy metabolism and anti-inflammatory processes, and helping the body to manage stress. Mineralocorticoids such as aldosterone also play a role in blood pressure regulation and blood volume, by managing sodium and potassium levels in the bloodstream.

WHAT CAUSES ADDISON’S DISEASE?

The most common primary cause of Addison’s disease is immune mediated destruction of the adrenal glands, leading to a decline in adrenal gland hormone production.

It is most commonly diagnosed in young to middle-aged dogs (average 4-5 years), and females are over-represented.

SIGNS AND SYMPTOMS

The relative lack of adrenal gland hormones (cortisol and aldosterone) lead to a wide range of changes and signs which may include:

• Reduced appetite
• Lethargy/weakness
• Weight loss
• Vomiting and diarrhoea
• Dehydration
• Reduced blood pressure > collapse

Signs wax and wane in many affected dogs, especially in the earlier stages of the disease process.

DIAGNOSIS

Clinical suspicion of Addison’s disease may arise based on the typical history and signs as listed above. As with any dog presenting in an unwell state, the veterinarian will recommend blood tests to evaluate things like red and white blood cell counts, hydration, kidney function, liver parameters, and electrolyte levels. Most typical cases of Addison’s disease will demonstrate a hallmark change in electrolyte balance on these screening blood tests, as well as a range of other changes.

To reach a confirmed diagnosis, the veterinarian will perform an ACTH stimulation test, which evaluates the adrenal gland function.

TREATMENT

When Addison’s disease is confirmed in patient who is very unwell, they are usually very dehydrated. Initial treatment generally includes hospitalisation and intravenous fluids to correct dehydration and address electrolyte imbalances.

Medication to address the deficiencies of glucocorticoid and mineralocorticoid hormones also commences immediately. In our hospital, we generally commence two medications in combination – cortisone acetate (Cortate®) and fludrocortisone acetate (Florinef®).  Once stabilised, the animal may go home, however the medication is ongoing and taken for life. Follow up evaluation of general progress and blood testing to check certain parameters (especially electrolyte levels) will be recommended, and dose adjustments will be made accordingly. Once stable and going well, evaluation with blood tests is generally recommended every 6 months, as many patients require further dose adjustments from time to time.