Pheochromocytoma in Dogs

A pheochromocytoma is a tumor of the adrenal gland, which causes the glands to make too much of certain hormones. This can cause an increase in heart rate, blood pressure, and breathing rate. These symptoms are intermittent (not present all of the time) because the hormones that cause them are not made all of the time or are made in low amounts.

Pheochromocytomas are rare in dogs. They usually occur in dogs that are older than seven years but can occur in younger dogs as well. Because this tumor affects an endocrine gland that functions to spread hormones, pheochromocytomas commonly spread to organs that are near them and can rapidly metastasize to other areas of the body.

Symptoms and Types

• Weakness
• Shaking
• Collapse
• Lack of appetite (anorexia)
• Lack of energy (lethargy)
• No interest in usual activities (depression)
• Vomiting
• Panting
• Rapid breathing (tachypnea)
• Increased urination (polyuria)
• Increased thirst (polydipsia)
• Diarrhea
• Weight loss
• Pacing
• Seizures
• Bloated abdomen
• Symptoms may seem to come and go
• Occasionally no symptoms

Causes

Pheochromocytoma is labeled idiopathic, since there is no known cause for this condition.

Diagnosis

Your veterinarian will need a thorough medical history of your dog's behavior, health and onset of symptoms. A rapid heart rate (tachycardia) is sometimes found during the physical examination. Your veterinarian will palpate your dog's belly to see if a mass can be felt or if there is extra fluid is present. Sometimes, there will not be anything that appears to be abnormal during the examination. Standard blood work, including a complete blood count, biochemical profile and urinalysis will be ordered. These will indicate how well your dog's internal organs are working and whether there are any infections present in the body. Your veterinarian may also order a special blood test which tells whether the adrenal gland is functioning normally. Your dog's blood pressure will be taken, and in some cases, the blood pressure will be very high, indicating hypertension.

If your dog's heart rate is very high, or its heart seems to have an abnormal rhythm, your veterinarian may order an electrocardiogram (ECG) to check the electrical capability of the heart. Your veterinarian will also order x-rays and/or ultrasound images of your dog's abdomen and thorax (chest). If there are abnormalities of the internal organs, they may show up on an x-ray or ultrasound image. Further diagnostic tests may include a computed tomography (CT) scan or magnetic resonance image (MRI). These imaging tools are higher sensitivity tests, which can give a more detailed picture of your dog's internal organs. To confirm a final diagnosis, your veterinarian will need to take a biopsy of the adrenal gland for laboratory analysis. It is common for dogs with a pheochromocytoma to have more than one medical problem diagnosed and treatment will be approached according to which condition is most critical.