25 May 2013

I blame names

Try your hand at a question from one of our anatomy exams: What nerve supplies the obturator internus muscle (a muscle in the pelvis)? The correct answer is the "nerve to obturator internus." It's like answering who is buried in Grant's Tomb.

As a time-strapped medical student, it feels like a godsend when a medical term is named in an obvious way. Even a lay person can intuit the meaning of medical terms like "urinary tract infection," "vocal cord paralysis," and "foot drop." Unfortunately, the meanings of medical terms are rarely so obvious.

Sometimes I can decipher the meaning of a medical term by looking at its Latin or Greek roots. "Nephrectomy", the surgical removal of a kidney, is a combination of "nephro-", from the Greek root for "kidney", and "-ectomy", from the Greek root for surgical excision. By knowing roots like these, I can decipher the meaning of a new term. Thus, a ureterectomy is the surgical removal of a ureter. A nephroureterectomy is the surgical removal of a kidney and a ureter. An appendectomy is the surgical removal of the appendix. Similarly, I can tell from its name that the supraclavicular artery runs above the clavicle, and that the ovarian artery supplies the ovary. It's fantastic.

But even this approach can run me into trouble. In 1806, a dermatologist named a particular skin disease "mycosis fungoides", from the roots for "mushroom" and "fungus", because it looks like a fungal infection. We now know that it is a type of lymphoma, with nothing to do with fungus or infection. But the name has stuck. Similar examples abound.

Often a medical term has no connection its meaning. Sometimes this is because the disease is named after its discoverer. Berger's disease affects the kidney, whereas Buerger's disease affects the small arteries of smokers.

The worst offenders are when medical terms are simply numbered in the order of their discovery. Our white blood cells have a category of proteins on their surface called "cluster of differentiation". The various proteins have been numbered from CD1 up to CD350. For some CD proteins, we need to have memorized which subcategories of cell types express them: for example,

CD3: T-cell;
CD4: Helper T-cell (depleted in AIDS);
CD8: Killer T-cell;
CD15: Reed-Sternberg cell (seen in certain leukemias);
CD30: Reed-Sternberg cell;
CD56: Natural killer cell;

and so on.

Exams like our national boards are chock-full of questions that test whether you realize that "lupus anticoagulant" is erroneously named, or that IL5 stimulates allergic reactions while IL10 tamps them down. Memorizing all of this takes a lot of time.

I maintain that time spent memorizing these silly names is time not spent learning other things, like how to heal patients. Medical nomenclature is needlessly complex. We should try to make our names for things easier to decipher.