Sen. Kennedy and the Brain Tumor: Zebras, Not Horses

A well-worn phrase in the world of medicine is, "When you hear hoofbeats, think horses, not zebras." The idea is that when you're trying to make a diagnosis, focus first on the most likely possibilities, not the rare and exotic (and often more fearsome) ones.

Well, Sen. Edward Kennedy wound up with a zebra.

After his seizure last week, many doctors suggested it may not have been a serious episode at all and might have no lasting effects. Seizures, they said, can be the result of medication reactions, undiagnosed diabetes, alcohol withdrawal, dehydration or an infection.

The Merck Manual says seizures can be triggered by emotional or physical stress, sleep deprivation and fever.

Seizures are linked to strokes, but Kennedy's physician and many experts seemed fairly confident that his seizure was not triggered by a stroke.

Which is to say: People were listening--and probably hoping--for horses.

The malignant glioma located above Kennedy's left ear is a particularly powerful zebra. It's not curable. It insinuates itself throughout the brain--"glia" is ancient Greek for "glue"--often making surgery perilous and ineffective. Two years after diagnosis, fewer than 10 percent of patients with this type of tumor are alive. Older patients fare worse. 

The temptation after hearing news like this is to think you hear zebras everywhere. In fact, seizures are very common--about 10 percent of people have one some time during their lifetimes. A large majority are caused by things other than brain tumors.

Yes, zebras are out there. But keep in mind that most of the time, you're just hearing horses. #

The National Cancer Institute has thorough information on malignant gliomas.

The American Cancer Society published this statement about malignant gliomas after Kennedy's diagnosis was announced.

MSNBC has a particularly useful article on the gliomas.