Correct diagnosis is the sine qua non for the care of any patient with any disorder. If you don’t know the diagnosis, you can’t establish the cause, provide the prognosis, or institute appropriate therapy. For patients with dermatologic disorders, a working diagnosis is almost always first established on the basis of clinical symptoms and signs. If necessary, this clinical diagnosis can subsequently be confirmed through procedures such as biopsy, cytology, and microbial culture (see Chapter 4).

There are two major approaches to using clinical symptoms and signs to establish a working diagnosis: the use of visual memory and the use of a morphologically determined approach. Dermatologists, by virtue of repeated exposure to patients with both common and uncommon diseases, almost always depend on visual memory. And, because it works for them, they use that same approach when teaching medical students and other clinicians. Thus, in the classroom or at continuing medical education courses, they bombard their audience with clinical photo after clinical photo, leaving the participants with a jumbled mass of impossible-to-remember images of skin disease.

The use of visual memory works for the dermatologist because of sufficient, repetitive exposure to these diseases. But other clinicians, encountering fewer patients with mucocutaneous disorders, lack the opportunity for sufficient visual reinforcement to dependably recognize uncommon and rare diseases. By analogy, they are put in the position of someone attending a large gathering where they know only a few of the guests. In spite of many introductions, the names of those they have newly met quickly disappear from memory. At best, on a subsequent encounter, one might remember a face as vaguely familiar but find it impossible to identify the person by name. The same problem occurs for the nondermatologist in a clinical setting. In this situation, when faced with an unrecognized mucocutaneous disorder, one might futilely turn to a standard dermatology textbook but find that the diseases in it are organized on the basis of etiology or pathophysiology. This is, of course, of no help, as one must know the diagnosis first before it is possible to make use of the material contained in such a book. As a last resort, one might then end up paging through an atlas hoping to stumble on a disease that matches what was just found on examination of the patient. At best this offers a hit-or-miss approach, and even when it is helpful, it is an inefficient and mostly inaccurate approach to diagnosis.

A better diagnostic approach for the nondermatologist is the use of a diagnostic approach in which the disorders are organized on the basis of clinical morphology. This approach directs the clinician to a cluster of diseases that share similarities in appearance. Once having arrived at the correct group of diseases, one can scan the classification table (see Table 3.1) to identify the most appropriate chapter in this book. Then, with a quick reading about the characteristic diagnostic features for the diseases contained in that chapter, together with perusal of the associated clinical photos, one can arrive at the most likely diagnosis. This diagnosis, if necessary, can be confirmed by way of a biopsy or other diagnostic test (see Chapter 4). Note that this approach even allows a clinician to make a correct diagnosis of a disorder that he or she has never previously encountered.

Of course, to use a morphologic approach such as this, one must be able to describe in dermatologic terms the features that one has seen on clinical examination. This is not very difficult because, as is true for most “foreign” languages, a relatively small number of words can serve one’s basic needs. The dermatologic words that are required for this approach are listed and defined under “Terminology” in the previous chapter (see Chapter 2).