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People only see what they are prepared to see.

—Ralph Waldo Emerson

Whether you are viewing Figure 1-1 in a book, in an aquarium, or in the sea, you immediately recognize the image as a fish. Those of you who are more schooled in the classification of fish might recognize that this is an angelfish with the tail resembling the head of the angel and the posterior fins representing the wings. If you are truly prepared to see this fish in all its splendor, you would see the blue circle above its eye as the crown of the queen angelfish.


Queen angelfish (Holacanthus ciliaris). (Used with permission from Sam Thekkethil.

Making a diagnosis in medicine often involves the kind of pattern recognition needed to identify a queen angelfish. This is much the same as recognizing a beautiful bird or the painting of a favorite artist. If you are prepared to look for the clues that lead to the identification (diagnosis), you will see what needs to be seen. How can we be best prepared to see these clues? There is nothing more valuable than seeing an image or a patient who has the condition in question at least once before you encounter it on your own. The memory of a powerful visual image can become hardwired into your brain for ready recall.

In medicine, it also helps to know where and how to look to find the clues you may need when the diagnosis cannot be made at a single glance. For example, a 3-year-old girl presents with bad seborrheic dermatitis of the scalp and hand dermatitis that is not responding to typical treatments with selenium based shampoos and topical steroids (Figures 1-2 and 1-3). The prepared clinician knows that not all scaly erythematous rashes on the scalp and hands are dermatitis and looks for clues of psoriasis such as nail changes (Figure 1-4) or scaling erythematous plaques around the elbows and knees (Figure 1-5). Knowing where to look and what to look for is how an experienced clinician makes the diagnosis of psoriasis.


Scaling on the scalp of this 3-year-old girl was thought to be seborrheic dermatitis for one year. When the cradle cap did not go away with appropriate treatment another clinician looked for other clues of disease to determine that this was psoriasis. (Used with permission from Richard P. Usatine, MD.)


The same 3-year-old girl with scaling and cracking of the hands thought to be atopic dermatitis. It was not until another clinician looked carefully at the nails and knees that the correct diagnosis of psoriasis was made. Knowing where to look for the clues ...

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