Cushings Disease

Cushings Disease

(Also called Hyperadrenocorticism)

Overview

Cushings disease occurs when the body is producing an excess of the hormone cortisol which is involved in regulating the metabolism and is also a stress hormone, involved in the fight or flight response. It is mainly a disease of older, small breed dogs.

Cortisol is produced by the adrenal glands, small glands located adjacent to the kidneys. Its production is regulated by another hormone called ACTH which is released from the pituitary gland in the brain. This acts on the adrenals and stimulates them to produce cortisol when it is needed.

There are two main causes of Cushings disease:

1. A growth in the pituitary gland which is functional and secreting large amounts of ACTH, over stimulating cortisol production from the adrenal glands. The vast majority of these masses are benign, meaning they do not spread and this cause is called pituitary dependant Cushings. Dogs with pituitary dependant disease account for around 85% of dogs with Cushings.
2. The second cause, accounting for the remaining 15% of Cushings cases, is a growth of the adrenal glands itself, secreting excess cortisol, regardless of any higher control from the pituitary gland. These growths can be either benign ie. will not spread or malignant meaning they do have the capacity to spread to other parts of the body.

Clinical Signs

The most common signs seen are increased thirst (polydipsia), increased frequency of urination (pollakiuria) and a ravenous appetite (polyphagia). You may also see recurrent skin disease such as infections of the skin, thinning of the skin and areas of hair loss (alopecia). In advanced cases you may see hard, chalky deposits in the skin. These are calcium and it is a condition called calcinosis cutis. Muscle wastage and a pot bellied appearance are common and affected dogs can also pant excessively. 

If you see any of the above signs in your pet then they should be examined by a vet.

Diagnosis

The clinical signs and history may lead your vet to suspect Cushings but definitive diagnosis is not always straightforward and requires a series of blood tests. There are two main tests that your vet may perform to diagnose Cushings.

• An ACTH stimulation test: The hormone that controls cortisol production, ACTH, is injected into the animal and blood samples are taken before and around an hour afterwards to assess the body’s response to the hormone which is abnormal in animals with Cushings.
• A low dose dexamethasone suppression test (LDDST): In this test, dexamethasone, a steroid, is injected into the animal and again the body’s response is monitored with a series of blood tests but this time taken over several hours.

Both these tests take a few hours so you would need to leave your pet at the vets to complete the tests. Usually the blood then has to be sent to an external laboratory so the results will not be immediate.

In some cases, additional tests may need to be performed such as routine biochemistry and haematology to check the function of organs such as the liver and kidneys and to check red and white blood cell numbers. Occasionally imaging such as ultrasound may be used to look at the adrenal glands.

Treatment

Cushings cannot be cured but can be managed with daily medications which are needed lifelong after diagnosis of Cushings. Signs may take several months to resolve.

Vetoryl capsules are the product used to control Cushings. Vetoryl capsules contain a drug called trilostane which blocks the production of cortisol by the adrenal glands. Vetoryl capsules come in several sizes, 10mg, 30mg, 60mg and 120mg capsules. The dose is dependent on the animal’s weight and the exact dose of Vetoryl required will be advised by your vet.

Ongoing monitoring will be required once your pet has started Vetoryl therapy. This will usually consist of routine biochemistry and haematology and an ACTH stimulation test. These will usually be done at 10 days, 4 weeks and 12 weeks after starting treatment with Vetoryl and the dose of Vetoryl may need to be adjusted in the early stages to get the best control of the Cushings. Monitoring will then routinely be every 3-6 months depending on progress, the exact frequency of monitoring will be decided by your vet.

Vetoryl can have some side effects so if you see any lethargy, inappetance, vomiting, diarrhoea or weakness whist your pet is on Vetoryl therapy then stop treatment and consult your vet.