Cushing's Syndrome in Dogs: Symptoms and Treatment

Cushing's syndrome is characterized by elevated blood cortisol levels. Discover in the following content the implications of this endocrine disorder on canine health.

Written and verified by the veterinarian and zootechnician Sebastian Ramirez Ocampo.

Last update: 29 June, 2023

Cushing’s syndrome (also called Cushing’s disease) in dogs is caused by an alteration of the hypothalamic-pituitary-adrenal axis, which is responsible for regulating and producing the hormone cortisol in canines.

This condition – also known as hyperadrenocorticism – can have a significant impact on our pets’ health and quality of life. Continue reading these lines to learn the reasons why it occurs, the clinical symptoms, and the measures that can be taken for its treatment.

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

Research reported in the journal Canine Medicine and Genetics specifies that cortisol plays a key role in the physiological response to stress, because it prepares the body for situations that threaten survival. In addition, it intervenes in the metabolism of sugars, fats, and proteins, as well as in the control of blood pressure and the regulation of the body’s water balance.

The stimulus for its production begins in the hypothalamus, through the secretion of corticotropin-releasing hormone (CRH). This substance is responsible for activating the pituitary gland to generate corticotropin (ACTH). In turn, it stimulates the adrenal glands to secrete cortisol. The latter, also known as adrenals, are located above the kidneys.

Therefore, any alteration in this hormonal process leads to increased levels of cortisol in the blood, which causes Cushing’s syndrome in dogs. According to an article published in the journal General and Comparative Endocrinology, three main causes can be identified:

• Pituitary tumor: Accounts for 80% to 90% of cases of hyperadrenocorticism in dogs. The neoplasm, usually benign (adenoma), causes an overproduction of ACTH in the pituitary gland. This phenomenon stimulates the adrenal glands to secrete more cortisol than necessary.
• Adrenal tumor: Occurs in 15 to 20% of dogs with Cushing’s syndrome. In this case, neoplasms can be benign or malignant (adenoma or adenocarcinoma) and lead the adrenals to produce an excess of cortisol.
• Iatrogenic origin: Unlike the previous ones, hyperadrenocorticism is produced by continuous medication with glucocorticoid drugs such as prednisolone.

What symptoms does the dog have?

Although this disease can appear in any type of dog, older and obese dogs, as well as some breeds such as the Schnauzer, Jack Russell, Yorkshire Terrier, West Highland Terrier and Bichon Frisé are more prone to suffer from it. This is the claim of authors in the Journal of Small Animal Practice who analyzed more than 1000 cases of hyperadrenocorticism in pets.

According to a publication in the Journal of Veterinary Internal Medicine, among the main symptoms that can occur due to Cushing’s syndrome are the following:

• Polyuria and polydipsia: The animal urinates more frequently, so it drinks more water to compensate for the loss of fluids. It’s presumed that this is due to increased blood flow to the kidneys, due to cortisol.
• Polyphagia: There’s an increase in appetite and food intake. The dynamics involved in this disorder are unknown.
• Abdominal distension: Cortisol produces a weakness of the abdominal muscles, so the belly acquires a pendulum shape.
• Bilateral alopecia: This is generated by an atrophy of the pilosebaceous follicle. It’s easy to distinguish it from other dermal pathologies, as hair loss is symmetrical on both sides of the body.
• Other skin abnormalities: Such as hyperpigmentation, loss of elasticity and thickness, scaly lesions due to calcium deposits, and constant infections.
• Hepatomegaly: Due to the action of cortisol, there’s an increased deposit of glycogen in the liver, which increases its size.
• Obesity: Since cortisol is involved in lipid metabolism, its alteration leads to increased fat deposition in the body.
• Fatigue and generalized muscle weakness: Due to the catabolic action of cortisol.

In more severe and advanced cases of the disease, arterial hypertension, renal failure, diabetes, and central nervous system disorders may occur.

The American Kennel Club warns that owners often mistake the symptoms for signs of aging. This is because they appear gradually and it can take years before a clear medical picture is complete.

How is Cushing’s syndrome in dogs detected?

The diagnosis of hyperadrenocorticism in dogs is based both on the identification of clinical signs and on the results of different analytical tests. In these cases, it’s recommended to perform blood counts, glycemia, urinalysis, biopsies, radiographs, and ultrasound scans to know the functional state of the organism.

However, according to research published in the journal In Practice, there are two tests that allow a more accurate diagnosis of Cushing’s disease in dogs:

• ACTH stimulation test: This consists of injecting synthetic ACTH hormone, with the aim of stimulating the adrenal glands to produce cortisol. In dogs with hyperadrenocorticism, the response is exaggerated, while in dogs without this pathology the hormone levels are normal.
• Dexamethasone suppression test: This glucocorticoid drug is given to evaluate the response of the hypothalamic-pituitary-adrenal axis. On the one hand, healthy dogs should manifest low levels of ACTH secretion, because cortisol is provided by an exogenous source. However, in dogs with Cushing’s syndrome, ACTH and cortisol levels remain high.

On the other hand, it’s important to note that there’s an atypical form of Cushing’s syndrome in dogs. In this regard, according to an article published in the journal The Veterinary Clinics of North America, the animal shows clinical signs and changes in various diagnostic tests.

However, both in the stimulation test and in the suppression test, the results are those of an average dog. For this reason, hyperadrenocorticism shouldn’t be ruled out if the tests are negative.

What measures are taken to treat it?

Treatment should be aimed at eliminating the cause of the excess cortisol, as well as normalizing the levels of the hormone and improving the patients’ quality of life.

As a study reported in The Veterinary Journal, the origin, and complexity of the condition will determine the most appropriate decision for treatment, which may be medicinal or surgical.

Pharmacological therapy

This is recommended for both pituitary and adrenal hyperadrenocorticism. In essence, drugs are used to control excessive cortisol production such as trilostane, which inhibits the synthesis of enzymes necessary for the generation of this hormone in the adrenal glands.

It’s important to emphasize that medication with this drug should be daily and for life.

Most patients usually improve within weeks of starting treatment. However, according to a study published in the Journal of Veterinary Internal Medicine, some side effects such as lack of energy, vomiting, diarrhea, and weight loss may  occur.

On the other hand, drug therapy can be complemented with radiotherapy to reduce the size of the tumors, especially those of pituitary origin. Other drugs that have been used in the treatment of Cushing’s syndrome in dogs are mitotane, ketoconazole, pasireotide, octreotide, and cabergoline.

Surgery

This is performed in cases of hyperadrenocorticism due to adrenal neoplasia. This is because surgical intervention of the pituitary brings many complications and puts the animal’s life at risk. The technique used is adrenalectomy, in which the complete removal of the gland with the tumor or both, if necessary, is performed.

Surgery isn’t recommended in cases that have developed metastasis to other organs or when the tumor is very vascularized. Among the main complications reported after surgery are pancreatitis and thromboembolism.

Finally, in iatrogenic hyperadrenocorticism, treatment consists of suspending glucocorticoid medication so that cortisol levels are gradually regulated. However, according to research reported in the journal Veterinary Clinic of North America, the symptoms may persist for weeks or months after discontinuation of the medications.

What is the prognosis and life expectancy of a dog with this disease?

According to studies published in the Journal of the American Veterinary Medical Association and in the journal The Veterinary Record, dogs under medical or surgical treatment have an average life expectancy of 2 to 3 years. Some of the complications reported in these investigations – which are related to poor prognosis – include hyperphosphatemia, pancreatitis, renal failure, metastasis, and thrombocytopenia.

Despite this, once Cushing’s disease is detected in dogs, therapy needs to be initiated to improve the quality of life of affected dogs. Similarly, early diagnosis can prevent most complications, so it’s important to make regular visits to the veterinarian.

Proper care for your dog

Having quality diets and strict control of cortisol levels during treatment can help increase your pet’s life expectancy. Always remember to give your pet the necessary love and attention during this difficult process. Just as in humans, the companionship of loved ones can make all the difference.