What triggers Cushings disease in dogs?

Cushing's disease is a condition in which the adrenal glands overproduce certain hormones. The medical term for this disease is hyperadrenocorticism.

The adrenal glands produce several vital substances, which regulate a variety of body functions and are necessary to sustain life. The most widely known of these substances is cortisol, commonly known as cortisone. Decreased or excessive production of these substances, especially cortisol, may be life-threatening.

How does cushings disease occur?

There are three mechanisms by which this disease can occur. Regardless of the cause, the clinical signs are essentially the same. It is important to identify the type of Cushing's disease because the various forms are treated differently and each has a different prognosis.

Pituitary gland tumour

The most common cause of Cushing's disease (85% of all cases in dogs) is a tumour of the pituitary gland. The tumour may be either benign or malignant and it causes the pituitary to overproduce a hormone that stimulates the adrenal glands to produce cortisol. The tumour may be microscopic or large. Depending on the size of the tumor, clinical signs other than Cushing's disease may be present. Generally, if the activity of the adrenal gland can be controlled, many dogs with this form of Cushing's disease can live normal lives for many years, as long as they take their medication and stay under close medical supervision. Growth of the pituitary tumour would give the patient a less favorable prognosis.

Adrenal gland tumour

Cushing's disease may be the result of a benign or malignant tumour of the adrenal gland. If the tumour has not spread into surrounding structures or other organs, then it may be possible to surgically remove the tumour (along with the adrenal gland) and cure the disease. If the tumour has already spread then surgery may not be possible and the prognosis is less favourable.

Iatrogenic

Iatrogenic Cushing's disease means that the excess of cortisol has resulted from excessive administration of a glucocorticoid. This may occur from oral or injectable medications. Although the injections or tablets were given for an appropriate medical reason, their use is now detrimental.

What are the clinical signs in dogs?

The most common clinical signs associated with Cushing's disease in dogs include:-

• an increase in appetite, 
• an increase in water consumption, 
• an increase in urination. 

Some dogs may also experience:-

• lethargy, or lack of activity,
• decline in coat quality.

Many of these dogs develop a bloated or "pot-bellied" appearance to their abdomen due to an increase of fat within the abdominal organs and a stretching of the abdominal wall as the organs get heavier. The pot-bellied appearance also develops because the muscles of the abdominal wall become weaker. Panting and increased appetite are other common findings with this disease.

How is Cushing's disease diagnosed?

Hyperadrenocorticism can be a challenging disease to diagnose and confirm. However, the testing process is crucial to determine the best treatment options and prognosis for your pet.

The two most common tests to detect Cushing's disease are the ACTH Stimulation Test and the Low-Dose Dexamethasone Suppression (LDDS) test. Other tests may be needed to determine which form of the disease is present. Endogenous ACTH levels, High-dose Dexamethasone Suppression (HDDS) test, urine cortisol: creatinine ratio, and 17-hydroxyprogesterone response to ACTH administration tests may also be recommended.

An abdominal ultrasound examination may also be a valuable part of the diagnostic process. In itself an ultrasound will not be able to determine if a patient has Cushing's disease, but it will permit the visualisation of the adrenal glands. This can then help determine their size, the presence of any unusual tissue and enable an ultrasound guided biopsy to be performed to determine if the tissue is cancerous.

What are the treatment options?

Treatment options depend greatly on the form or the cause of the Cushing's disease:

Iatrogenic

Treatment of this form requires a discontinuation of the corticosteroid that is being given. This must be done in a controlled manner so that complications associated with the discontinuation of the medication do not occur. Unfortunately, it usually results in a recurrence of the disease that was being treated by the corticosteroid. Because there may have been adverse effects on the adrenal glands, treatment in the form of medication may also be needed.

Adrenal Tumour

Treatment of an adrenal tumour requires major abdominal surgery. Although this is a high risk surgery, if successful and the tumor is not malignant, there is a good chance that the dog will regain normal health. If surgery is not an option, some of these patients can be managed with medication, as discussed below.

Pituitary Tumour

Treatment of the pituitary-induced form of Cushing's disease is the most complicated. There are two drugs used in Australia: Lysodren and Trilostane.

Lysodren is the primary drug used to destroy the abnormal adrenal gland tissue. Lysodren is also known as mitotane or o,p'-DDD. If too little of the drug is used, the abnormal adrenal tissue persists and the disease continues. If too much is used, most or all of the adrenal cortex will be destroyed, which can be life-threatening and result in reduced hormone production by the adrenal glands. This condition is known as Addison's disease or hypoadrenocorticism. Therefore, careful monitoring of the dog is necessary in order to achieve good results. Because the pituitary is not being affected by the treatment, it continues to stimulate the adrenal gland. This means that lifelong treatment is necessary.

Trilostane is a synthetic steroid analogue that works by reducing the production of cortisol levels. It currently needs to be imported from the UK and requires daily or twice daily dosing for life. It can therefore be cost prohibitive.

Although a cure is not achieved with either treatment, control is possible for many years if the tumour is small. If the tumour is large, local effects of the tumour invading surrounding tissues in the brain can be the limiting factor in quality of life.

Cushing's disease is a serious condition in dogs that can lead to severe, sometimes life-threatening conditions and illnesses. Our Charlotte vets explain what causes Cushing's disease in dogs, as well as the symptoms and treatments.

What is Cushing's disease in dogs?

Cushing's disease (hyperadrenocorticism) is a serious health condition in which the adrenal glands overproduce cortisol (cortisone) in the body. Excess cortisol can put a dog at risk of several serious conditions and illnesses, from kidney damage to diabetes, and can be life-threatening.

Cushing’s disease is commonly caused by a benign or malignant tumor in the pituitary gland, a pea-sized gland located at the base of the brain. In some cases the tumor could be located on the adrenal glands, located just above the kidneys.

Excessive cortisol can also result from the prolonged use of steroids, called iatrogenic Cushing's syndrome. 

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

The most common symptoms of Cushing’s disease seen in dogs include:

• Increased appetite
• Excessive thirst or drinking
• Thinning of the skin 
• Hair loss
• Frequent urination 
• Muscle weakness
• Enlarged abdomen, potbellied appearance
• Panting
• Lethargy

If your dog has Cushing’s disease you will see at least one of these symptoms, however it is uncommon for all of these symptoms to be present. 

It is essential to contact your vet immediately if your dog is displaying any of the symptoms above. Dogs with Cushing’s disease have an increased risk of diabetes, kidney damage, blood clots, and high blood pressure.

How is Cushing’s disease diagnosed?

Your vet will do a physical exam and run a few tests to determine what may be causing your pet's symptoms and to rule out other health problems. The tests can include, but are not limited to, urinalysis, urine culture, complete blood panel, and/or full chemistry panel.

Your vet may run adrenal function tests, testing adrenal low dose and high dose dexamethasone suppression test. However, adrenal function tests can result in false positives when another disease with similar clinical signs is present.

An ultrasound may help to rule out other conditions that could be causing your dog’s symptoms. Other diseases that may cause similar symptoms include tumors in the spleen or liver, bladder stones, gallbladder disease, gastrointestinal disease, chronic inflammatory liver disease.

The most effective diagnostic testing for Cushing’s disease is magnetic resonance imaging (MRI) which allows your vet to assess your dog’s adrenal glands. However, this testing method can be expensive. 

At Carolina Veterinary Specialists, our vets are trained to diagnose and treat a wide range of internal diseases and conditions. We have access to diagnostic imaging tools and treatment methods to identify and manage these issues.

What are the treatments for Cushing’s disease in dogs?

Cushing's disease in dogs is typically treated with medications that help decrease the amount of cortisone that the adrenal glands produce. The only way to cure Cushing's disease is to remove the tumor, however because of the complexity and risks of surgery, most cases are treated with medication.

Treatments will vary depending on the type of Cushing’s disease your dog has.

Pituitary tumor. Treatment of pituitary dependent Cushing’s disease is the most complicated. Two drugs, trilostane and mitotane are commonly used. 

Adrenal tumor. Treatment of an adrenal dependent Cushing’s disease usually requires major abdominal surgery. If the entire tumor is able to be removed and the tumor is not malignant, there is a good chance that your dog will regain normal health. 

Iatrogenic Cushing’s disease. Treatment requires gradual discontinuation of the steroid, usually resulting in a recurrence of the disease that was being treated by the steroid.  

After starting the medication treatments your dog will need to see the vet regularly for ACTH stimulation tests, until the excessive production of cortisone is controlled.  

Over their lifetime of your pet, routine monitoring of blood tests and medication adjustments need to be made. 

Is Cushing's disease fatal in dogs?

The cause of your dog's Cushing's disease as well as the conditions your pup develops that are linked to the disease are going to impact your pet's prognosis. Early diagnosis and treatment are essential for limiting the severity of the disease.

The symptoms of Cushing’s disease can be minimized with diligent observation and long-term management. 

Most dogs can be successfully treated with few medication side effects. However, the wrong dose can cause mild or severe side effects. Therefore, your pet must be carefully monitored and follow-up blood tests are essential.

Dogs who do not receive adequate monitoring and followup often experience relapses and severe illness or death, as a result of complications.

Note: The advice provided in this post is intended for informational purposes and does not constitute medical advice regarding pets. For an accurate diagnosis of your pet's condition, please make an appointment with your vet. 

Is your dog exhibiting symptoms of Cushing's disease? Contact us right away! Our Board Certified Veterinary Specialists and Emergency vets provide advanced diagnoses and treatment for Charlotte pets.