Editor's Note
Sorting Out Hoof Beats
The case started like a spy movie with whispered conversations by friends: “She’s just not herself, and she’s acting strange. Her husband is also acting strange.” When she arrived at my office, her symptoms weren’t too much more specific—lack of appetite, inability to think straight, and a strange feeling in her legs. Her physical exam was normal except that she just didn’t track with my questions. Her answers were vague, not what you would expect from a bright ICU nurse. At the end of our visit, I probed the possibility of depression since she had become more reclusive and was missing work on a regular basis. I also considered chemical dependency.
I admitted her to the hospital, where I ordered a battery of chemistry tests and X-rays, a drug screen, and, for no reason I could justify at the moment, a urine test for heavy metals. All the initial test results were normal, and I recommended that she be seen by a psychiatrist for presumed depression. The psychiatrist promptly transferred her to an inpatient psychiatric ward.
Five days later, the result of the heavy metal screen came back showing a high level of arsenic. I called her psychiatrist who was then her attending physician. A few weeks later, I got a call from the patient thanking me and letting me know that “this was not an accident.” Subsequently, her husband was tried, convicted, and jailed for attempted homicide. I still ponder whether making this diagnosis was crack clinical acumen or blind luck.
Such cases form the grist for doctors’ lounge conversations, physicians trading stories of great cases, fascinomas, or zebras—that colorful description derived from the adage, “When you hear hoof beats, think horses, not zebras.” For decades, zebras have inhabited the New England Journal of Medicine column Case Records of the Massachusetts General Hospital, where such obscure diseases as Castleman’s seem as common as high blood pressure. Zebras have long fed the fascination of practicing physicians and the nightmares of medical students, who frequently “acquire” the rare and scary diseases they study.
Intrigued by zebras, we tapped our readers for stories of unusual cases they’ve seen and were rewarded with six case studies. We profiled Daniel Lachance, a Mayo Clinic neurologist who was central to the investigation that identified the mysterious illness that struck Austin meatpacking workers. Like a Poe mystery, a zebra story is enticing, as well as educational.
Perhaps coined by Theodore Woodward, M.D., a former professor at the University of Maryland, the zebra saying is shorthand for the rule of medical judgment that says “look for common things first.” Medical students and residents learn to rank their differential diagnoses with the most likely at the top and the New England Journal Case Records diagnoses near the bottom. It’s a heuristic technique that works most of the time. But like any rule, its exceptions can be treacherous.
No physician wants to miss a zebra. Yet spotting them is becoming increasingly complicated. What’s a zebra depends on where you practice and where your patients have been. More than ever, sorting out the hoof beats during a physician’s day requires keeping an open mind when a “horse” looks a little strange, doesn’t quite sound or smell right, or doesn’t fit the textbook description. It means not automatically discounting vague symptoms like “feeling weird.” And it means taking friends seriously when they say, “she’s acting strange.”
Charles R. Meyer, M.D., editor in chief
Dr. Meyer can be reached at
cmeyer1@fairview.org