10 October 2012

Diagnosis II

A patient at the free clinic complained that over the past few years he had lost most of his ability to taste and smell. "I put lots of spices on my food, but it barely tastes like anything."

The patient clearly had "hyposmia," a decreased sense of smell. It's potentially worrisome, because it can be an early sign of degenerative brain diseases like Parkinson's and Alzheimer's. It could also be a symptom of a brain tumor. I wanted to get to the bottom of whatever was going on. How could I approach this diagnosis?

I did so by breaking the action of smelling into its constituent parts.
  • First, air carrying a scent is transported to the bridge of the nose, where olfactory receptors reside.
  • Next, the olfactory receptors fire. They send a signal along nerves that traverse the skull and enter the brain.
And so, there are two main categories of causes of diminished sense of smell:
  • Conductive: a problem getting air to the olfactory receptor. Usually treatable.
  • Sensorineural: A problem affecting the olfactory receptors, the nerves, the skull, or the brain. Usually permanent.
Now my job was to figure out what category of hyposmia the patient had. So, I asked a simple question: "Have you ever managed to temporarily regain your sense of smell?" The patient had. He had bought a nasal spray from the dollar store, and when he used it, for a few hours he regained some of his sense of smell.

Although the patient couldn't remember the name of the spray, it didn't matter. I now knew that the patient had conductive hyposmia. We ended up prescribing him a nasal steroid, which would help improve breathing through his nose. And he didn't need to get a head CT, which is expensive and would needlessly expose him to a hefty dose of radiation. I made this diagnosis methodically, drawing on my knowledge of the mechanisms of disease.

I've learned how to formulate diagnoses by reading textbooks and medical journal articles entirely about how to do them properly. Diagnosis as a stand-alone academic subject has been given only a superficial treatment in our classes. I like studying it on my own because I see the art of diagnosis as fundamental to the practice of medicine.