What is Cushing’s disease?

Cushing’s disease is the production of excess hormones from the adrenal glands.  The adrenal glands are found above the kidneys and produce hormones which are necessary for the function of many systems in the body such as helping regulate body weight, skin health, mineral balance, blood pressure and modulating the immune system.

What are the symptoms of Cushing’s disease in dogs?

Cushing’s disease usually effects older dogs. The symptoms can be subtle, coming on quite slowly and are such that an owner may just associate them with normal aging. Your pet may suffer with only one symptom or many.  Signs to look out for are:-

• Bulging, saggy belly
• Hair loss on elbows progressing to flanks and abdomen
• Increased thirst
• Frequent urination
• Increased appetite
• Skin thins and is easily damaged and slow to heal
• Recurring urinary tract infections
• Increased panting

What are the causes of Cushing’s disease in dogs?

The disease has two distinct causes.  Pituitary dependant hyperadrenocorticism (PDH) is the most common cause of Cushing’s disease (approx. 80% of cases) and involves excess production of the hormone ACTH from the pituitary gland.  The pituitary gland is located in the brain where it releases ATCH, stimulating the adrenal gland to produce the hormone cortisol. In the majority of cases, excess production of ATCH is caused by a benign pituitary tumour. It can be treated by drug therapy but cannot be cured.

The other form of Cushing’s disease is adrenal-based hyperadrenocorticism (ADH) which is usually caused by an adrenal tumour, which can be benign or malignant. As with PDH, adrenal based Cushing’s disease results in the overproduction of the hormone cortisol.

A dog can exhibit symptoms of Cushing’s disease as a result of steroid treatment for another illness.  In such cases, once the steroid treatment has stopped, the symptoms of Cushing’s disease will stop too.

What are the risk factors of Cushing’s disease?

Cushing’s disease affects middle aged and older dogs of both sexes. Some breeds of dog are considered at an increased risk of developing Cushing’s disease.  Those include Beagles, Boston terriers, Boxers, Dachshunds and Poodles.

Diagnosis

Your vet will want to review your dog’s medical history and examine your dog for symptoms. Where a vet suspects Cushing’s disease, a complete blood count, chemistry profile and urinalysis with be undertaken, before making a provisional diagnosis.  If these test results indicate Cushing’s Disease, further tests will be necessary for a definitive diagnosis and the cause (PDH or ADH) to enable your vet to effectively treat the disease.

A further test, called an ACTH test, may be undertaken to measure the level of the hormone cortisol in the blood.  As cortisol levels very from hour to hour in a healthy animal, a number of samples will need to be taken, before and after your pet has been given an injection of a hormone (ACTH). An injection of ACTH will stimulate your dog’s adrenal glands to produce cortisol.  Once the samples have been analysed, the results will indicate whether the adrenal glands are functioning properly.

A low dose dexamethasone suppression test can sometimes help determine which type of the disease your pet is suffering from. When a healthy dog is given a low dose of dexamethasone, he would show a noticeable decrease of cortisol in the blood whereas a dog with Cushing’s disease would show no decrease.

Your vet may also choose to undertake an ultrasound to measure the size of the adrenal glands. If one is larger than the other, this is likely to indicate the presence of a tumour.  If both are enlarged, a pituitary tumour is likely to be the cause.

What treatment is there for Cushing’s disease in dogs?

The treatment offered depends on the cause of the disease and severity of the symptoms.  If symptoms are mild and not potentially dangerous or distressing (i.e. High blood pressure, recurrent infections, urinary accidents) your vet is unlikely to prescribe any medication but suggest regular check-ups so that your pets condition can be monitored.  If medication is prescribed your pet will still need to be closely monitored for side effects and that the appropriate dose is being prescribed.

If an adrenal tumour has been identified, surgery may be possible, however, the decision to operate will very much depend on the type of tumour and whether oral medication will be sufficiently effective. If the tumour is benign and successfully removed, it can cure the condition.

Can Cushing’s disease be prevented?

Cushing’s disease cannot be prevented but early diagnosis may result in your pet receiving more effective and less invasive treatment. Take your pet for regular check-ups and notify your vet of any early symptoms you have noticed.