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Pheochromocytoma is an uncommon, but serious condition that primarily affects middle-aged to older dogs, although any dog can be susceptible. This disease is characterized by an adrenal gland tumor, located near the kidneys, which results in an overproduction of adrenal hormones. These excessive hormones can lead to a range of symptoms that may significantly impact your dog's quality of life. This article provides a comprehensive guide to understanding pheochromocytoma in dogs, including the causes, symptoms, diagnosis, and most importantly, management options.
Pheochromocytoma is a tumor of cells that arises within the adrenal medulla of the adrenal glands. The adrenal glands release substances that play a crucial role in regulating various bodily functions, including blood pressure, heart rate, and metabolism.
With a pheochromocytoma, there is an overproduction of catecholamines such as epinephrine (adrenalin) and norepinephrine. The symptoms are a reflection of the body's response to the excessive amounts of these hormones.
Pheochromocytomas in dogs are often malignant, with reported metastasis in up to 40% of cases. Metastasis may occur in various organs such as the liver, spleen, lungs, regional lymph nodes, bones, and central nervous system.
Up to 60% of dogs with pheochromocytoma are asymptomatic and can have incidental findings. Signs of tumor presence are often vague and nonspecific. The most common symptoms include:
Other reported symptoms include lack of appetite, restlessness, seizures, panting, cough, exercise intolerance, abdominal distension, vomiting, and diarrhea.
Diagnosing pheochromocytomas can be quite challenging, as they can present symptoms similar to other diseases.
Your veterinarian will start with a physical exam. Often, the physical exam is normal, especially as the signs and symptoms can wax and wane.
Routine blood testing is often unrewarding as there are no changes that would be specific to diagnosing a pheochromocytoma. Blood pressure measurement should be performed as the vast majority of dogs (>80%) with pheochromocytoma have elevated blood pressure (hypertension).
Radiographs of the thorax and abdomen are recommended for evaluation. Thoracic radiographs aid in assessing the cardiovascular system and screening for pulmonary cancer metastasis, which is present in around 15% of dogs at the time of diagnosis. Abdominal radiographs can detect a large adrenal mass if present.
An abdominal ultrasound is a valuable tool for evaluating the size, shape, and structure of the adrenal glands, as well as for clinical staging. In approximately 75% of affected dogs, an adrenal mass can be detected through ultrasound. The ultrasound cannot differentiate between a benign or malignant adrenal tumor.
While measuring adrenal hormones exists in people to diagnose pheochromocytoma, there are no assays available for dogs.
The treatment of choice for pheochromocytoma is the removal of the affected adrenal gland, also known as adrenalectomy. As this surgery is very complex, having your dog referred to a major referral center such as a university veterinary hospital is recommended.
However, surgery may not be possible in all cases. In those situations, medical management can help control the symptoms and improve your dog's quality of life. Phenoxybenzamine is recommended to help manage high blood pressure in dogs with a nonresectable mass or when surgical intervention is not viable. Phenoxybenzamine works by relaxing the smooth muscles in blood vessels, resulting in a decrease in blood pressure.
A preliminary study conducted with toceranib (Palladia®) in dogs diagnosed with inoperable or metastatic pheochromocytoma showed significant clinical improvements. More research needs to be performed however to validate this treatment method.
Dogs that undergo surgery have the potential for a positive outcome. According to a study, the median survival time after surgery was found to be 374 days. Some dogs can even live for 2-3 years, with approximately 60% reported to have a 3-year survival rate.
It is worth noting that dogs with large adrenal tumors measuring or documented metastasis have significantly shorter survival times.
In closing, pheochromocytoma is an uncommon yet serious tumor in the adrenal gland that primarily affects middle-aged to older dogs. It results in excessive production of adrenal hormones, leading to various symptoms such as weakness, weight loss, and in severe cases, collapse and blindness.
Diagnosis can be challenging and typically involves a series of tests including blood pressure measurement and abdominal ultrasound. The preferred treatment is surgical removal of the affected adrenal gland, although medications like Phenoxybenzamine can help manage symptoms in cases where surgery is not an option.
The prognosis varies but can be positive, particularly when the condition is detected early and appropriate treatment is provided. If you suspect that your dog may be affected, it's important to promptly consult your veterinarian for a thorough evaluation and a customized treatment plan.
