Thursday, April 6, 2017

The Lonesome Zebra

Eddie pants nervously as I part his fur and examine the lump that Mr. Williamson is concerned about.
I'm about to comment on it when Mr. Williamson asks the inevitable question, "Have you seen something like this before?"
To which I reply, "Yes, I have. Many times. Daily in fact. But that doesn't mean much." And then I explain myself briefly. But as you and I have a lot more time right now, and as you are presumably more interested in these things than the average person, I will explain myself at much greater length here.

It begins with the fact that humans are excellent at pattern recognition. This is largely a good thing and it is one of reasons our distant ancestors were able to avoid being eaten on the savannas of Africa. Our brains are strongly wired to match everything new we encounter with past experience, whether consciously or unconsciously. That particular type of rustle in the tall grass? Could be a lion. Better keep quiet and slowly retreat.

However, in medical diagnosis pattern recognition is a problem. Some symptoms are what we call "pathognomic", meaning that they are specific to one particular disease, but the great majority are not. A red eye can be due to dozens of conditions. Coughing has scores of causes. And poor appetite can quite literally have hundreds of explanations. In veterinary school they try to beat pattern recognition out of us and replace it with a "problem oriented" diagnostic process. I won't explain what that is. Trust me that it is as boring as it is important.

Eddie's lump is small, loose under the skin, smooth in contour and slightly rubbery in firmness. Pattern recognition dictates that this is almost certainly a lipoma, which is a benign fatty growth. But only "almost certainly". Eddie has never had one before - most dogs with lipomas have several - so I am wary of falling into that trap as a type of cancer called a mast cell tumour can feel very similar. I suggest collecting a few cells with a needle. Eddie is good for this as he is far more worried that I might be planning to trim his nails, which he hates more than anything in life. The needle aspirate just produces fat cells, so thankfully it is just a lipoma.

So what about the zebra advertised in the post title? I apologize if you read this hoping for another wacky patient story,  but no, nobody has consulted me about their zebra problems. Which is a good thing (see my previous post: "A Mile Wide"). Instead I am referring to an old aphorism taught to every medical and veterinary student which highlights the flip-side of this issue: "When you hear hoof-beats, don't think of zebras." In other words, although a set of symptoms could be the result of a bizarre rare disease, the common diseases are far more... common. Consequently veterinarians have to exercise some balance and judgment and avoid freaking pet owners out with a laundry list of horrible possibilities, accompanied by a wildly expensive diagnostic program.

Balance. Judgment. Tricky things. Don't obsess about the zebras, but don't ignore them either.

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