Dr. Morgan Wills writes…
For many of us, the natural tendency is to jump straight to diagnosis. Some of our volunteers who saw the patient did just that: “Roundworm,” said one. “Hickeys?!” wondered another. Interesting possibilities for sure, but a systematic approach was needed.
Now, despite our modern infatuation with laboratory tests and radiologic studies, the key to a medical diagnosis almost always lies in taking a careful history. However, one of the major exceptions to this dictum is the field of dermatology. In Derm, at least as many of us were taught, the first rule in making a diagnosis is to describe the appearance of the finding.
So, what do you see?
The questions we should ask about a rash are actually pretty straightforward. Such as:
– Are there discrete lesions?
– What shape?
– What size?
– What color?
– Are they flat or raised? (hint to the digital audience: these are flat)
– Any other noteworthy characteristics?
Based on these observations, the clinician can build what we call a differential diagnosis—a short list of possible diagnoses. What kinds of skin problems would be on your “differential dx” for this patient?
We’ll give you a few days to ponder it before offering the answer. In the meantime, though, we’ll give you a hint: the patient did not seem very concerned about the rash…