Canine Cushing's Syndrome/Disease

Cushing's Syndrome occurs when the adrenal glands (located near the kidneys) overproduce hormones. The adrenal glands normally produce several hormones to regulate body function, including:

• Cortisol: a hormone responsible for stress responses
• Aldosterone: a hormone responsible for balancing electrolytes (such as sodium and potassium)

Cushing's Syndrome (an overproduction of these two hormones) is the opposite of Addison's Disease when the adrenal glands do not produce enough hormones.

Excess adrenal hormones affect many systems and can cause:

• Instable endocrine system
• Skin infection
• Inflammation of the pancreas
• Blood clots
• High blood pressure
• Diabetes
• Urinary tract infections
• Excess protein in the urine
• Other illnesses

Cushing's syndrome is one of the most common hormonal disorders in middle-aged to older dogs.

CAUSES:

There are three possible causes of Cushing's Syndrome, each with different treatment and prognosis:

1. Pituitary Tumor (most common): a benign tumor grows on the pituitary gland in the brain, which over-stimulates the adrenal glands to produce excess cortisol
2. Adrenal Tumor: a benign or cancerous tumor grows on the actual adrenal glands, causing them to produce excess cortisol
3. Iatrogenic Cushing's Disease: Prolonged use of any drug containing cortisone

SIGNS:

• Hair thinning
• Increased drinking and urination
• Increased hunger
• Lethargy
• Muscular weakness and exercise intolerance
• Pot-bellied abdomen
• Panting
• Seizures
• Disorientation

DIAGNOSIS:

Your veterinarian may perform 2 types of blood tests, which will usually be enough to make a diagnosis:

• ACTH stimulation test: The veterinarian injects ACTH, which stimulates the adrenal glands to release cortisol, measuring the amount that is produced
• Dexamethasone suppression test: The veterinarian injects Dexamethasone, which normally suppresses cortisol output, measuring the amount of cortisol produced

Other tests may include:

• Urine test: an examination of cortisol to creatinine ratio
• Radiographs: checks the abdomen
• Ultrasound: checks the adrenal glands
• MRI: checks the pituitary glands
• Skin biopsy: for dogs that show hair loss
• Nerve and muscle biopsies: for dogs that have an abnormal gait

It is necessary to determine if Cushing's syndrome was caused by a growth on the pituitary gland or on the adrenal gland because the treatments and prognoses differ.

TREATMENT:

Treatment depends on the cause:

• Pituitary Tumor: Can be managed but not cured with medication. You will have to make follow-up visits to your veterinarian who may recommend dose changes
• Adrenal Tumor: In 50% of cases, this tumor is benign. In the other 50% of cases, this tumor is cancerous. With a benign tumor, surgical removal cures the disease. With a cancerous tumor, surgery may help
• Iatrogenic Cushing's disease: Stop the use of the drugs containing cortisone Ask your veterinarian how to do this gradually to avoid other complications

PROGNOSIS:

• Pituitary Tumor: With a quick diagnosis, life-long medication, and regular health checks, most dogs can live out their years unaffected. However, if the tumor continues to grow, the prognosis is not as good
• Adrenal Tumor: With a benign tumor, your veterinarian will give a guarded prognosis. With a malignant tumor, the prognosis is not good
• Iatrogenic Cushing's disease: Gradually, your pet will show improvement after you stop the medication

Medically Reviewed by Sara Ochoa, DVM