12 August 2012

Going zebra-hunting

The aphorism handed down to medical students like myself goes: "When you hear hoofbeats behind you, don't expect to see a zebra." In medical parlance, "zebras" are rare diseases. Zebras are those obscure diseases that a doctor learns about in medical school and then never encounters again.

Recently I went zebra-hunting on the hospital wards. While the professor showing me around checked on an ill patient with a failing organ, I noticed at the patient's bedside table a large tub of fancy imported licorice. Some of the licorice had already been eaten. I asked the patient if she likes licorice. She responded that she loves the stuff, and eats a substantial amount every day.

What the patient didn't know was that a compound in licorice, glycyrrhizic acid, inhibits an important enzyme found in the adrenal glands. Consuming moderate-to-severe amounts of licorice can cause certain medical problems (like hypertension and fluid retention) that would have been particularly harmful for this patient. I brought this up to the medical team, and they told her to stop eating licorice.

Another patient had episodes of disabling, unremitting headaches that would last for weeks. I suspected hemicrania continua, a rare headache disorder that seemed to fit the case quite nicely.

I had read somewhere that those most likely to diagnose rare diseases are old doctors (because they've seen everything) and those still in training (because they spend a disproportionate amount of their time learning about rare diseases). I am still early in my training. It's not clear to me whether the reason I am finding zebras is because my eye is keen or because I don't know what I'm doing. I'm becoming increasingly confident that it is the former.

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