When you hear hoofbeats...

   There is a commonly-repeated aphorism in medicine: "When you hear hoofbeats, think of horses, not zebras." This was coined in the 1940's by Dr. Theodore Woodward, who encouraged his medical interns to consider common illnesses (horses) as the cause of a patients symptoms, before immediately leaping to the rare diseases (zebras) which tend to capture our imaginations.

We saw these guys in 2007 in South Africa (where zebras may be more common than horses...).

   I don't fault trainees for thinking of exotic zebras before commonplace horses. It is partly human nature, and partly a by-product of our medical education which uses rare illnesses to illustrate broader principles.  This is because much of what we learn about how our bodies work comes from studying uncommon situations where these systems go haywire.

   For example, we know about vitamin C because we wanted to understand why sailors got scurvy - a nasty condition characterized by bleeding gums, non-healing wounds, and eventually neurological problems and death.  For several centuries there were various theories about the cause of scurvy, as well as various cures prescribed - some of which worked, and some didn't. It wasn't until the 1930s that we had the conclusive answer, when it was demonstrated that giving Vitamin C to guinea pigs who were otherwise fed a grain-only diet would cure them of scurvy.  Vitamin C's current name of ascorbic acid (or "anti-scurvy acid") was given because of those studies.  Through studying scurvy, we learned about the myriad processes in our bodies which depend on Vitamin C.  We also learned that humans (and fortuitously enough for science, guinea pigs) are sort of freaks in the animal world.  Most other animals can synthesize their own Vitamin C.  Humans, along with many other primates, just happened to inherit a faulty Vitamin C gene, which doesn't cause us any problems, unless we have a very imbalanced diet.

   Every medical student learns about vitamin C and scurvy, but few physicians today have ever seen a case (myself included).  That said, every time I hear "bleeding gums", the diagnosis of scurvy immediately pops into my mind, even though gingivitis (or an anticoagulant medication, or a host of other causes) is much more likely to be the culprit.  At least Dr Woodward's aphorism reassures me that I am not the only person guilty of thinking of zebras before horses.

I'm not worried about scurvy in Laos. Mangoes have way more Vit C than oranges. 

  As a third-year medical student, I remember rounding on a 40-year old man who was recovering from a relatively minor illness.  He was improving nicely, and was very anxious to get home to attend to his business.  As per routine, we asked how he was feeling that morning.  He casually mentioned he had a bit of a headache - a feeling of tightness around his head.  Another medical student asked him if it was the worst headache of his life, to which patient responded "As a matter of fact, I suppose it is worse than the headache I usually get".  When our supervising physician asked my colleague about the cause of the headache, he replied uncertainly, "Morning headache, worst of his life - possibly a brain tumor?".  It was, actually nothing more than a simple tension/stress headache, which a brief exam and a few questions revealed pretty conclusively.

   It wasn't my colleague's fault that in our first 2 years of med school we only learned about the more "sexy" causes of headaches - things like migraines, or increased pressure inside the skull (hence his guess of a brain tumor).  Tension headaches, were not something any of the classroom teachers found particularly interesting to discuss, since they didn't teach any obvious physiological principles.

   Once we began to work with patients, we quickly learned to shift focus.  We couldn't forget completely about the zebras that our education had emphasized, but now we needed to think first about horses.  Since then, and now that I have practiced as a generalist pediatrician for the past 10 years, it is very natural that hoofbeats first make me think of horses.  After all the majority of what I have seen day-to-day has been fairly common presentations of common conditions, with the occasional 1%er zebra to keep me from getting too complacent.  When I hear about a 6 year old's abdominal pain before getting on the school bus I first think about anxiety or constipation, rather than pancreatitis.  Horses, not zebras...

   Now that I am in Laos, however, I have had to change the filters through which I see the world.  Unlike Maryland, where Dr. Woodward encouraged his interns to consider horses, Laos doesn't have many horses (and probably not a single zebra for that matter), but there are plenty of water buffalo.  So, now when I hear hoofbeats, I think of water buffalo.

Water buffalo walking up a bank of the mekong.

   In America, a profoundly anemic toddler is probably drinking too much cows milk (a horse), or maybe has a severe occult bleed, or something worrisome like leukemia, or bone marrow suppression. In Laos, a profoundly anemic toddler almost certainly has thalassemia (a water buffalo).

This young girl has such a pale thumbnail bed, due to anemia from thalassemia. Her total volume of circulating red blood cell mass was only 1/6 of normal.

   In America, a two month old presenting in acute heart failure probably has a congenital heart condition.  In Laos, that same presentation probably means beriberi, aka thiamine deficiency. In fact, in Laos we assume any infant with fussiness, weakness, heart failure, weak cry, stridor, decreased reflexes, signs of meningitis, or a whole host of other symptoms, probably has beriberi, perhaps the biggest pediatric water buffalo of them all.  We don't forget to think of other diagnoses, but they all get a shot of thiamine in their thighs, because assuming that this particular water buffalo is a horse could quickly result in death.

Adding to the list of our common water buffalo are typhoid/enteric fever, dengue fever, Japanese encephalitis, infantile staphylococcal scalded skin syndrome, and chickenpox - which has gone from being one of the most common of horses in the US to one of the rarest of zebras. In fact, chickenpox is such a common water buffalo in Laos that many cases of impetigo are misdiagnosed as chickenpox.  I guess we all have our biases when it comes to hoofbeats.