Opinion: Rheumatologists Cautioned Against Wasteful Testing to Find Rare Diseases

What rheumatologist doesn’t love the good old zebra hunt? You know—the pursuit of diagnosing the extraordinarily rare disease purely through pluck and wits. The zebra hunt is almost a tradition, a perennial topic of polite, but subtly boastful, conversation among peers and the subject of numerous career-building case reports. The hunt also happens to be incredibly enjoyable: It validates the years of memorizing otherwise trivial information and gives us license to demonstrate the keenness of our diagnostic skills. Much like big game hunting in real life, zebra hunts have a dark side. The joy that we take in identifying the rare or exotic diagnosis is countered by very real dangers for our patients.

First and foremost, the idea of categorizing diseases as zebras or horses comes from a bygone era. The term originated in the 1940s at the University of Maryland when Dr. Theodore Woodward, MD, wisely instructed his students that, “When you hear hoof beats, think of horses, not zebras.”1 During his time, humanism in medicine was a novelty, and a doctor’s role was defined narrowly as a healer of specific disease. Now, we know that doctors should be more than just diagnostic machines; we ought to treat patients holistically in more than just the context of disease. Indeed, the idea of horses and zebras makes no sense: All patients should be considered unique, no matter how common or rare their diseases are. Moreover, we shouldn’t be too eager to jump on an exotic diagnosis; instead, we should focus on how best to recover the patient’s sense of well-being. All too often, there is a misplaced sense of personal glory that comes with diagnosing a rare disease, rather than due consideration to what it means to the patient.

Secondly, we spend a great deal of resources in pursuit of each zebra. Over the past decade, we have come to acknowledge that there is a tremendous amount of waste that goes into inappropriate investigations. We often look down on the primary care physician who orders an ANA for chronic fatigue on the odd chance that he or she may have lupus, but we don’t seem to have the same condescension when we order entire panels of tests to check a patient for any number of rare diseases, particularly when the pre-test likelihood is next to nil. And when one of these antibodies comes back positive, which is bound to occur when so many are sent at the same time, we often get excited and hail our trophy, instead of scrutinizing our practices. This, of course, doesn’t mean that we shouldn’t work up patients in whom there is reasonable clinical suspicion for a rare disease, but it does mean that we should have at least a good reason.