What is Hyperadrenocorticism (Cushing’s Disease) in Dogs?

Introduction

For months, Jennifer had been observing some unusual changes in her loyal Boston Terrier, Bella. She noticed that Bella had developed a pot-bellied appearance, was losing hair, and seemed to be constantly hungry and thirsty. Concerned about her canine companion’s well-being, Jennifer scheduled a visit to her veterinarian. After a series of tests, the vet delivered the unexpected news that Bella had Cushing’s Disease, a condition Jennifer had never encountered before.

Cushing’s disease is a rare endocrine disorder where dogs develop excessive production of cortisol (a hormone produced by the adrenal glands). This is also called Hyperadrenocorticism. The excess cortisol affects many body systems, including bones, muscles, skin, eyes, heart, blood vessels, lungs, liver, kidneys, pancreas, brain, immune system, reproductive organs, gastrointestinal tract, thyroid gland, and others.

It is caused by too much ACTH (adrenocorticotropic hormone) or too little CRH (corticotropin-releasing hormone), which stimulates the pituitary gland to produce ACTH. In most cases, Cushing’s syndrome occurs because of an adenoma tumor in the pituitary gland. This condition is called primary Cushing’s Syndrome.

However, some dogs develop this condition after having surgery to remove a benign pituitary tumor called a craniopharyngioma.

Two Common Types of Cushing’s Disease

There are two types of Cushing’s syndrome: pituitary-dependent and adrenocortical-dependent.

• Pituitary-dependent Cushing’s syndrome occurs when the hypothalamus, part of the brain that controls hormone production, produces too much corticotropin-releasing factor (CRF). As a result, an abnormally functioning pituitary gland causes most cases of Cushing’s syndrome
• Adrenocortical-dependent Cushing’s syndrome, on the other hand, occurs due to excessive amounts of ACTH produced by the cells of the anterior lobe of the pituitary gland. Both forms of Cushing’s syndrome require treatment.

Causes of Cushing’s disease in dogs

Hypercortisolemia, also known as Cushing’s disease, is caused by increased cortisol production. There are three primary forms: pituitary gland tumor, adrenal adenoma, and idiopathical hypercortisolism (IH). Treatment options include surgery, radiotherapy, chemotherapy, immunotherapy, and medical management.

Pituitary Gland Tumor

This condition is caused by a benign growth called a pituitary adenoma. Unfortunately, about 90% of dog breeds with Cushing’s disease have a pituitary gland tumor. Pituitary adenomas are tumors that develop in the pituitary gland, a part of the brain located just above the nose. Most pituitary adenomas grow slowly over the years, but some overgrow and become life-threatening.

There are two types of pituitary adenomatous tumors: nonfunctional and functional.

• Nonfunctioning tumors tend to grow larger than functioning ones, but both types can lead to problems. Therefore, nonfunctioning tumors are typically diagnosed during routine physical exams.
• Functional tumors, however, can sometimes cause problems without causing apparent symptoms. When this happens, owners may notice behavioral changes, such as aggression toward other animals or increased sexual activity.

Adrenal Adenoma

Adrenal adenomas are benign tumors that grow in the adrenal glands. These tumors usually affect middle-aged dogs, although they can develop at any age. Symptoms vary depending on the location of cancer. However, some common symptoms include lethargy, vomiting, diarrhea, weight loss, increased thirst and urination, and decreased appetite.

An adrenal gland is located above each kidney and produces hormones that regulate blood pressure, heart rate, metabolism, and other functions. An adrenal adenoma is an adrenal tumor that grows slowly over the years. Because of their slow growth, these tumors are sometimes misdiagnosed as cysts.

Idiopathical Hypercortisolism (IH)

Idiopathic hypercortisolism (IHC), also called Cushing’s disease, is a rare condition in dogs characterized by excessive production of cortisol, a hormone produced by the adrenal glands. Cortisol levels are typically elevated due to increased activity of the pituitary gland, which stimulates the release of ACTH, a hormone that triggers cortisol synthesis.

This disorder is uncommon in dogs, although it affects both sexes equally. Most cases of IHC are diagnosed during routine screening tests performed by veterinarians.

Some common clinical signs of IHC include weight gain, lethargy, vomiting, diarrhea, polyuria, polydipsia, muscle weakness, alopecia, skin lesions, and behavioral changes. These symptoms usually develop gradually over several months. However, some owners report noticing hair loss before an accurate diagnosis.

Dogs with IHC tend to respond favorably to treatment with prednisone, a corticosteroid drug. Treatment is typically started at low doses and slowly tapered off over several weeks. Although the prognosis for recovery is generally favorable, long-term complications associated with chronic steroid administration can include osteoarthritis, diabetes mellitus, obesity, and other conditions.

Symptoms of Hyperadrenocorticism in Dogs

The symptoms of Cushing’s disease usually appear gradually after many years of the disease. In some cases, however, they show up suddenly.

• Weight Loss – Your dog might lose weight without realizing why. For example, he could eat less than usual or stop eating altogether.
• Muscle Weakness – Muscles become weak because of low protein levels in their bodies. They don’t work as well as normal muscles do.
• Bone Problems – Bones weaken and break easily. Dogs who get Cushing’s disease often develop arthritis.
• Skin Changes – Hair becomes thin and brittle. It falls out in patches. Some dogs’ hair turns gray. Their skin looks dry and scaly.
• Heart Failure – High blood pressure damages the walls of the arteries. Blood clots form inside them. When these clots break off, they travel through the bloodstream until they reach another body part. A clot in the brain can lead to seizures. A lump in the lungs can block airflow into the lungs.

A veterinarian will recommend treatment based on the severity of clinical signs and the extent of organ damage. Treatment options include surgery to remove the affected part of the brain, radiation therapy, and medications. Medications typically consist of drugs called corticosteroids, which reduce inflammation and slow down cell division.

Diagnosis of Cushing’s Disease in Dogs

Blood tests are done to know if your dog has Cushing’s disease. These tests measure how much cortisol is present in the bloodstream. However, blood tests do not tell whether the disease is active or inactive.

To determine if your dog has Cushing’s disease, your veterinarian will perform abdominal ultrasound imaging of the adrenals. An ultrasound machine uses sound waves to produce images of internal diseases found in organs.

Ultrasounds can show enlarged adrenal glands but cannot distinguish between normal and abnormal gland sizes. Therefore, a CT scan or MRI may be performed to look for signs of tumor formation.

If your dog does not respond to treatment, it may require surgery to remove the diseased adrenal gland(s). Surgery is usually successful in treating Cushing’s disease.

Treatment and Prevention for Canine Cushing’s Disease

Treatment for Cushing’s disease depends on whether the condition is acute or chronic. If the dog suffers from acute Cushing’s disease, it will likely recover entirely within a few days. However, dogs diagnosed with chronic Cushing’s disease require long-term medical management. Treatment options include surgery, radiation therapy, chemotherapy, and medication.

Surgery

Surgery involves the removal of part of the adrenal gland but has risks and benefits. The risk of surgery includes bleeding, infection, and death. The benefits of surgery involve removing the source of excess cortisol production and restoring hormone levels to normal.

While the decision to undergo surgery depends mainly on the severity of symptoms, medications are typically recommended for dogs who experience milder symptoms.

Radiation therapy

Radiation therapy works by destroying cancer cells that are producing too many hormones. It is often used when no evidence of cancer metastasis (spread) exists. Radiation therapy is also an alternative to surgery for some types of tumors.

Different radiation treatments could be considered, including external beam radiotherapy, brachytherapy, proton beam therapy, and stereotactic radiosurgery.

Chemotherapy

One treatment option is chemotherapy. Chemotherapy involves giving drugs intravenously or orally to treat malignant tumors.

While chemotherapy treats certain cancers effectively, it can also harm healthy cells. Because of this, it’s essential to discuss the pros and cons of chemotherapy with your veterinarian before deciding whether or not to proceed with the medication treatment method.

Medications

Because Cushing’s disease is rare, few studies are available to learn more about it. However, it’s possible to treat dogs who suffer from the condition with medication. Two drugs are used to treat Cushing’s disease: glucocorticoids (steroid hormones) and mineralocorticoids (hormone analogs).

Glucocorticoids are usually prescribed to control symptoms, while mineralocorticoids are used to prevent complications.

There are three different forms of glucocorticoids: prednisolone, dexamethasone, and betamethasone

1. …Prednisolone is the most commonly used drug, but it is associated with side effects like vomiting, diarrhea, and increased appetite.
2. Dexamethasone is less likely to cause these side effects but can cause decreased appetite, lethargy, and skin infections.
3. Betamethasone is another option but it tends to cause more severe side effects like vomiting, diarrhea, and ulcers.

Mineralocorticoids are typically given in combination with glucocorticoids. Fludrocortisone is the most common mineralocorticoid used to treat Cushing’s disease. It is taken orally daily, effectively reduces blood pressure and controls water retention.

Frequently Asked Questions