What is Cushing’s disease?

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Cushing’s disease (also known as hyperadrenocorticism) is named after Henry Cushing who first described the disease in humans in 1912.

It is one of the most common conditions affecting a dog’s endocrine system and mostly occurs in smaller dogs aged over seven years. The disease causes dogs to produce excessive amounts of cortisol, which helps regulate the body’s metabolism and immune system. Too much cortisol can impact a dog’s entire body.

What causes Cushing's disease?

There are two different types of Cushing’s. The first is adrenal dependent hyperadrenocorticism (ADHA). This occurs when a tumour on the adrenal glands causes them to overproduce cortisol.

The second type is pituitary dependent hyperadrenocorticism (PDHA). PDHA is the more common of the two forms, and the most common cause is benign tumours in the pituitary gland, accounting for up to 85 per cent of cases. The pituitary is known as the master gland because it controls the hormone release from other endocrine glands, including the adrenal glands. In most cases of PDHA, the tumours cause it to overproduce the ACTH hormone, which stimulates the adrenal glands to produce cortisol.

Excessive use of some steroid-based medicines (mostly used to treat allergies, some cancers, and immune disorders) can bring about an onset of the disease, even after the steroids have been stopped.

What are the symptoms of Cushing's disease?

There are numerous signs and symptoms which can point to Cushing’s disease, and as these are shared with many other illnesses — for example, diabetes and urinary tract infections — it can be tricky to identify.

Symptoms include:

  • Increased thirst/appetite.
  • Increased urination or night-time urination.
  • Distended (pot-bellied) abdomen.
  • Loss of hair.
  • Lethargy.
  • Obesity.
  • Recurring infections.
  • Muscle weakness.
  • Panting even when resting.

How is Cushing's disease diagnosed?

If you suspect your dog might have Cushing’s disease, your vet will test his blood and urine for levels of cortisol. If he suspects Cushing’s, he may also order two further tests: ACTH stimulation test, in which the function of the adrenal glands is measured, and a dexamethasone suppression test to measure how cortisol levels change when injected with dexamethasone. Once a diagnosis of Cushing’s has been confirmed, a test to determine which form, either ADHA or PDHA, will be in order.

What is the treatment and prognosis of Cushing's disease?

The most common treatment is medication such as Vetoryl, which will reduce the amount of cortisol produced in the adrenal glands. The dog will then be blood tested a few weeks later to check that the dosage is correct for him.

For dogs with ADHA, surgery to remove the tumour can be an option. PDHA-affected dogs can benefit from radiotherapy to shrink the tumour. Cushing’s is a life-long condition, but as long as the disease is controlled by medication, and your dog has regular check-ups and blood tests, he can enjoy a good quality of life.

Avoiding Addison's disease

Occasionally, if a dog’s cortisol levels are significantly reduced as a result of treatment, he can develop Addison’s disease (hypoadrenocorticism). The opposite of Cushing’s, one of the main symptoms is a lack of appetite. Other symptoms include lethargy, shaking, weight loss, and an increased thirst. Another ACTH test will be in order if your vet suspects your dog has Addison’s disease.

Top tip!

If there are any changes in your dog’s food or drink intake, see your vet to get him checked out.

The major glands in a dog’s body

  1. Testes (dog)
  2. Ovaries (bitch)
  3. Pancreas
  4. Adrenal
  5. Parathyroid
  6. Thyroid
  7. Pituitary