Cushing's Disease in Dogs

Article written by veterinarian Isabelle Vixège

Cushing's disease in dogs in 3 key points: 

• Cause: excess cortisol, the stress hormone
• Symptoms: a dog that drinks a lot and loses its hair
• Treatment: trilostane (Vetoryl®, including Vetoryl 10 mg), a veterinary medicine

Cushing's syndrome, Cushing's disease or hyperadrenocorticism, all these terms designate a common endocrine pathology in dogs. Resulting from an excess of cortisol in the blood, it requires an accurate diagnosis. Treatment for Cushing's disease helps to alleviate symptoms and prolong the life expectancy of affected animals.

Summary

1. Cushing's disease in dogs, what is it?
2. What are the symptoms?
3. What are the causes?
4. How is it diagnosed?
5. What is the treatment? Can it be cured?

1. Cushing's syndrome in dogs, what is it?

Cushing's syndrome or hyperadrenocorticism is a pathology characterized by a high level of cortisol in the body. It results from a dysregulation of the adrenal glands.

Cortisol is an essential hormone. Produced by the adrenal glands under the control of the pituitary gland from cholesterol, it plays many roles. It notably allows adaptation to stress by optimizing the release of sugar to supply vital organs such as the heart or brain, or muscles. This is why it is often called the "stress hormone".

Therefore, an increase in blood cortisol linked to acute or chronic stress can also be found in canids. This is then referred to as functional hyperadrenocorticism, which should be differentiated from Cushing's disease.

There is also iatrogenic Cushing's syndrome in dogs, resulting from corticosteroid treatment. These medications will have the same effect as an excessively high cortisol level (they are from the same family) and cause the same clinical signs. Stopping the treatment generally resolves this syndrome.

Hyperadrenocorticism also affects other species such as horses, cats (very rare), hamsters, and humans.

Did you know?

This syndrome was named after the American neurosurgeon (Harvey Cushing 1869-1939), a pioneer in brain surgery. He was the first to demonstrate the responsibility of pituitary adenoma in the occurrence of the syndrome that now bears his name.

2. What are the symptoms of a dog with Cushing's disease?

An increase in cortisol levels is useful in cases of temporary stress. However, if the excess persists, it will become detrimental and affect many tissues. The most frequently encountered symptoms in dogs are:

• Polyuria-polydipsia (increased thirst and urination)
• Polyphagia (increased appetite) with weight gain
• Alopecia (symmetrical hair loss on the chest and abdomen)
• Thinning of the skin with the appearance of comedones
• Increased abdominal volume (a dog with a swollen belly)
• Ligament laxity
• Fatigue

Here are some photos of the symptoms of Cushing's disease:

Swollen belly in a sick dog (Cushing's syndrome)

Comedone on the body of a dog with Cushing's disease

Canine hyperadrenocorticism primarily affects middle-aged to elderly animals. Certain breeds are predisposed, such as the Yorkshire Terrier, Jack Russell Terrier, Poodle, Dachshund, and German Shepherd.

In addition to visible clinical signs, cardiac (hypertension) and hepatic repercussions are constant. Diabetes can also occur. One of the most serious and dreaded complications is thromboembolic accident; it consists of the formation and migration of blood clots that block blood vessels.

Without treatment, the disease slowly progresses to a worsening of symptoms and shortens the dog's life expectancy, even leading to death.

3. What are the causes of Cushing's disease in dogs?

Cushing's syndrome in dogs is caused by elevated cortisol secretion by the adrenal glands (2 small glands located in the abdomen near the kidneys). These glands are themselves dependent on another gland: the pituitary gland, located at the base of the brain. The pituitary gland produces a hormone, ACTH (Adrenocorticotropic Hormone), which stimulates the adrenal glands.

Thus, hyperadrenocorticism in dogs can be caused by two types of tumors:

• A benign tumor (micro- or macro-adenoma) of the pituitary gland leading to an overproduction of ACTH, causing the adrenal glands to overreact.
• A tumor (benign or malignant) of an adrenal gland leading to hyperactivity of that gland (approximately 15% of cases).

4. How is Cushing's disease in dogs diagnosed?

The diagnosis of Cushing's syndrome in dogs involves various complementary examinations which must, of course, be carried out in a veterinary clinic. These assessments should only be undertaken in animals presenting typical symptoms of Cushing's disease and clinical signs.

Once suspicion is raised, there are several specific blood or urine tests to confirm hyperadrenocorticism. Veterinarians often use an ACTH stimulation test: cortisol levels are measured before and after injection of an ACTH analogue. In cases of Cushing's syndrome, the levels in the second analysis are greatly increased, as cortisol is in excess.

Imaging (ultrasound, CT scan, MRI) allows differentiation of the origin of the syndrome (adrenal tumor or pituitary tumor); this is crucial for management.

5. What is the medical treatment? Can this tumor be cured? What is the prognosis?

The treatment to combat this disease will aim to reduce symptoms, increase the quality of life (for both the dog and its human), and extend the dog's life expectancy. The prognosis for life is therefore not compromised.

• Surgery

It involves the removal of the tumor (in the case of adrenal or pituitary tumors). While surgical options can be curative, in practice, they are rarely performed due to the risks and surgical complications. In the case of a cancerous adrenal tumor, metastases may already be present, limiting the life expectancy and survival time of the sick animal even after successful surgery.

• Radiotherapy

It is indicated for the treatment of macroadenomas of the pituitary gland and yields good results.

• Medical treatment

In dogs, the medication used to treat Cushing's syndrome is trilostane. This molecule inhibits an enzyme involved in cortisol synthesis by the adrenal glands. This medication is generally administered once a day in capsule form. This medical treatment requires regular veterinary follow-up to determine the correct dose and avoid potentially severe hypocortisolism. As an indication, a blood test is recommended every 3 months once the treatment is well established.

Given the burden (daily administration of treatment) and cost of this medical treatment, and the slow progression of Cushing's disease in dogs, it may sometimes be decided not to treat the animal, but to simply monitor it. This is particularly the case if the symptoms are mild. Nevertheless, it is important to note that some insurances reimburse this type of medical treatment.

In cases of Cushing's disease in dogs, collaboration between the owner and the veterinarian is therefore fundamental to ensure a long and high-quality life for the affected pet.

Article written by Dr. veterinarian Isabelle Vixège