Cushing’s disease in dogs: what it is, how to spot it and how it is treated

Cushing’s disease, also known as hyperadrenocorticism, is one of the more common endocrine disorders in dogs. It results from an excess of cortisol, the stress hormone produced by the adrenal glands. A persistently raised cortisol level has serious consequences for a dog’s health and can lead to a range of problems. Recognising the signs and reaching a diagnosis early are therefore crucial, so that the dog can be treated appropriately and enjoy a better quality of life.

What causes Cushing’s disease?

Cushing’s disease can have several causes, and it is these that determine how it is treated:

• Pituitary-dependent (the most common): in over 80% of cases the disease is caused by a benign tumour of the pituitary gland. The tumour secretes a hormone (ACTH) that drives the adrenal glands to produce excessive amounts of cortisol.
• Adrenal-dependent: in around 15–20% of cases the disease is caused by a tumour (benign or malignant) on one or both adrenal glands. This tumour produces cortisol independently of the pituitary.
• Iatrogenic: this form of Cushing’s disease is brought on by giving a dog excessive doses of corticosteroid medication over a long period, for instance when treating allergies or autoimmune disease.

Signs: what to look out for

The signs of Cushing’s disease come on gradually and can easily be mistaken for the ordinary effects of ageing. Over time, however, they become increasingly obvious. The most characteristic are:

• Increased thirst and frequent urination: the dog drinks far more water than usual, which means more frequent trips outside and sometimes even incontinence.
• Increased appetite: the dog seems never to be satisfied and constantly begs for food.
• Changes to the coat and skin: the coat becomes thin and dull, and symmetrical hair loss may appear on the abdomen and flanks. The skin grows thinner and is more easily damaged.
• A larger abdomen: the belly sags and takes on a “pot-bellied” look. This is the result of weakened abdominal muscles and an enlarged liver.
• Muscle weakness: the dog becomes listless, less keen to play, and struggles to climb stairs or jump.
• Panting and shortness of breath: the dog may pant even after very little exertion.

Diagnosing Cushing’s disease starts with a visit to the veterinarian, who may suspect the condition on the basis of the clinical signs and initial tests such as routine blood and urine analysis. What confirms the diagnosis, however, are specialist hormone tests, in particular the low-dose dexamethasone suppression test (LDDST). In addition, an abdominal ultrasound scan makes it possible to assess the adrenal glands and locate any tumours. Treatment is a long-term process and depends on the underlying cause. In the most common form, and in the adrenal form as well, medical treatment is used to bring the cortisol level down. These medicines are usually given for the rest of the dog’s life. If the disease is due to an adrenal tumour, surgery may be considered. Well-managed treatment keeps the disease under control and significantly improves the dog’s quality of life, allowing it to live normally for many years.

Cushing’s disease: which breeds are at risk?

Cushing’s disease can occur in a dog of any breed, but some are particularly predisposed to it. The condition is most often diagnosed in middle-aged and older dogs, usually from six years of age. The highest risk is seen in breeds such as the Poodle, Dachshund, Boxer, Beagle, Boston Terrier and Maltese. It is worth noting that these breeds are prone to the pituitary form of the disease, which is the most common. Less often, but still regularly, Cushing’s disease is also diagnosed in Golden Retrievers, Labradors and German Shepherds.