Cushing’s disease in dogs

Content by Dr Emma Chandley BVetMed PGCertSAS MRCVS 

Cushing’s disease is a hormonal condition caused by prolonged exposure to excessive levels of cortisol. Cortisol is an important hormone involved in metabolism, immune function and the body’s response to stress. But persistently high levels can affect many different organs.

The name Cushing’s disease is commonly used to describe pituitary-dependent hyperadrenocorticism, where a usually benign tumour of the pituitary gland produces too much adrenocorticotropic hormone (ACTH). This stimulates the adrenal glands to produce excessive cortisol.

A less common form occurs when a tumour develops within an adrenal gland and produces cortisol independently. Long-term treatment with corticosteroid medication can also cause signs of Cushing’s. This is known as iatrogenic hyperadrenocorticism.

• Cushing’s disease causes prolonged excess cortisol in the body.
• It’s most commonly diagnosed in middle-aged and older dogs.
• Increased drinking, urination and appetite are common signs.
• Panting, a pot-bellied appearance, muscle weakness and skin changes can also occur.
• Treatment can control the condition, but most dogs require long-term management.

There are several possible causes of hyperadrenocorticism. The most common is a small tumour of the pituitary gland, which results in excessive ACTH production and causes overstimulation of the adrenal glands. This is called pituitary-dependent hyperadrenocorticism (PDH) and accounts for the majority of naturally occurring cases.

A smaller number of cases are adrenal-dependent hyperadrenocorticism (ADH), where a tumour within an adrenal gland produces excessive cortisol. These tumours can be benign or malignant. Long-term administration of corticosteroid medication can cause a different form of hyperadrenocorticism, so your vet will consider your dog’s medication history when investigating the condition.

Cushing’s can affect any breed or size of dog, but it is more commonly diagnosed in middle-aged and older animals. Pituitary-dependent disease is reported more frequently in smaller breeds, while adrenal tumours are relatively more common in larger dogs.

Some breeds, including Miniature Poodles, Dachshunds, Boxers, Boston Terriers and Beagles, have been reported to have an increased risk. However, breed predisposition does not mean that an individual dog will necessarily develop Cushing’s disease.

Cushing’s usually develops gradually, and the signs can initially be quite easy to overlook.

Common signs include:

• Increased thirst
• Increased urination
• Increased appetite
• Panting
• A rounded or pot-bellied abdomen
• Muscle weakness or muscle loss
• Hair loss
• Thin or fragile skin
• Recurrent skin infections
• Lethargy or reduced exercise tolerance

Some dogs develop several of these signs, while others may initially have only one or two. Increased thirst and urination are particularly common. Your dog may drink considerably more than usual, need to go outside more frequently or start having accidents indoors.

Excess cortisol also affects muscle tissue and fat distribution, which can contribute to a pendulous abdomen and reduced muscle mass. Changes to the skin and coat are also common and may include thinning of the skin, hair loss and recurrent infections. As many of these changes can also occur with other illnesses, especially in older dogs, they do not automatically mean that a dog has Cushing’s.

Diagnosing Cushing’s disease is not always straightforward. There’s no single test that’s 100% accurate. Your vet will first assess your dog’s history, the clinical signs noted and routine blood and urine test results.

More specific blood tests are then generally recommended when there’s a reasonable clinical suspicion of hyperadrenocorticism, rather than simply because a laboratory abnormality is present. Routine blood tests may show changes associated with Cushing’s, including an increase in alkaline phosphatase (ALP), although these findings are not specific to the disease. Urine testing can also provide useful information.

If Cushing’s is suspected, your vet may recommend an endocrine test to assess how the adrenal glands are responding. The low-dose dexamethasone suppression test (LDDST) is commonly used as the initial screening test, while an ACTH stimulation test may be more appropriate in some patients. The choice of test depends on the individual dog, taking into account the clinical signs and whether other illnesses are present.

Once hyperadrenocorticism has been confirmed, further testing may be needed to determine whether the cause is pituitary or adrenal dependent. Abdominal ultrasound can assess the adrenal glands, while CT or MRI may be recommended in selected cases – particularly where assessment of a pituitary tumour is important.

Treatment depends on the underlying cause and the individual dog’s health. Most dogs with naturally occurring hyperadrenocorticism are managed medically. Trilostane is commonly used to reduce cortisol production and control the clinical signs. It does not remove the underlying pituitary tumour, so treatment is generally ongoing. Regular monitoring is essential because too little cortisol suppression can leave the disease poorly controlled, while excessive suppression can cause potentially serious problems.

Other medical treatments, including mitotane, may be considered in selected cases. Dogs with adrenal-dependent disease may be candidates for surgical removal of the affected adrenal gland. This can potentially be curative in appropriately selected dogs, but adrenal surgery is a significant procedure and careful assessment is needed before it’s recommended.

In selected dogs with pituitary-dependent disease, specialist treatments such as hypophysectomy or radiotherapy may also be considered. These options are generally available through specialist referral centres. Dogs receiving treatment need regular veterinary monitoring. Medication requirements can change over time, and blood tests and assessment of clinical signs help your vet determine whether treatment remains appropriate.

Cushing’s is generally a lifelong condition, especially when it’s caused by a pituitary tumour and managed medically. That said, with appropriate treatment and monitoring, many dogs can have a good quality of life for several years. The long-term outlook depends on the underlying cause, the dog’s age and general health, the presence of other diseases and how well treatment controls the excess cortisol.

Untreated Cushing’s can have serious consequences because prolonged cortisol excess affects multiple body systems. Dogs may be more prone to complications including hypertension, diabetes mellitus, recurrent infections, muscle weakness and thromboembolic disease.

“Cushing’s is one of those conditions that can creep up gradually, so owners don’t always notice how much their dog has changed. Increased drinking, more frequent urination, a bigger appetite, and heavier panting can initially seem relatively minor, particularly in an older dog.

“I often find that owners notice the changes more clearly when they look back over several months. They may realise that their dog has gradually become less active, lost muscle, developed a different body shape or started drinking much more than they used to.

“Diagnosing Cushing’s can be challenging as it may take lots of different tests to come to a diagnosis. The clinical signs and routine blood and urine results all need to be considered before deciding whether specific hormonal testing is appropriate.

“If the diagnosis is confirmed, regular monitoring is an important part of treatment because the aim is to control the disease without suppressing cortisol too much.

“The good news is that many dogs respond very well to treatment. Cushing’s is usually something we manage rather than cure. But with the right treatment and monitoring, affected dogs can continue to enjoy a good quality of life for years.”

Emma Chandley – BVetMed PGCertSAS MRCVS 

If you’re thinking about buying a Petgevity Lifetime Plus policy, we’ll consider all pre-existing conditions when offering cover for your dog* – including Cushing’s disease. 

When you apply for dog insurance, you need to let us know: 

• Which medical conditions they’ve had in the last two years 
• Their health status now

Find out more about Petgevity’s dog insurance for pre-existing conditions.