What’s a Pheochromocytoma, and How Do Vets Diagnose It?

This hormone-secreting tumor can form in horses’ adrenal glands, potentially causing damaging high blood pressure.
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There’s a hormone-secreting tumor that can form in the adrenal glands of horses, potentially causing damaging high blood pressure, but it’s so incredibly rare that only a handful of cases have ever been described in studies. Veterinarians don’t normally notice the tumor until the horse is on the post-mortem table, at which time it’s difficult to determine its significance (Did it kill the horse, or was it just an incidental finding?). But if veterinarians could know what combination of signs to look for, they could conceivably recognize the tumor—called a pheochromocytoma–in a sick horse with colic or internal bleeding, perhaps, and intervene, or at least not subject the horse to medications or treatments that could cause the case to worsen.

Daniela Luethy, DVM, a resident in large animal internal medicine at the University of Pennsylvania’s New Bolton Center, and colleagues both at Penn Vet and the University of California, Davis (her alma mater), reviewed records for 37 horses diagnosed with pheochromocytoma on post-mortem exam from 2007 to 2014 at both veterinary schools, aiming to identify common signs in the horse that might lead to a higher clinical suspicion of the tumors. She presented the material at the 2015 American Association of Equine Practitioners Convention, held Dec. 5-9 in Las Vegas.

“Pheochromocytoma is the most common adrenal medullary neoplasm of domestic animals,” she said, or, more simply, a tumor in a particular part of the adrenal gland, which lies in front of the horse’s kidneys (cranially, or toward the horse’s head). “It has been described in horses, dogs, cattle, and humans, and this tumor arises from the chromaffin cells of the adrenal medulla. These cells are responsible for release of catecholamines.”

The tumor can secrete high amounts of catecholamines, hormones that can cause a number of side effects in the horse’s body. In people, high levels of catecholamines associated with this tumor can lead to high blood pressure, headaches, and sweating

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Stephanie L. Church, Editorial Director, grew up riding and caring for her family’s horses in Central Virginia and received a B.A. in journalism and equestrian studies from Averett University. She joined The Horse in 1999 and has led the editorial team since 2010. A 4-H and Pony Club graduate, she enjoys dressage, eventing, and trail riding with her former graded-stakes-winning Thoroughbred gelding, It Happened Again (“Happy”). Stephanie and Happy are based in Lexington, Kentucky.

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