Running for the textbooks is not the way to diagnose skin lesions. A physician assistant specializing in dermatology offers some practical advice.

Have you ever seen a patient with a dermatologic problem and had no clue what it was? I get a sinking feeling in my stomach when I see skin lesions and have no idea what they are. Experienced dermatology providers can make sense of what they observe because they know what is common, how skin diseases manifest in certain parts of the body, the characteristics of various skin lesions, and the history that could explain them. To illustrate my point, here are some examples from my own practice.

Figure 1. Asteatotic eczema is common among older men

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Case 1

A 70-year-old man with very fair skin seeks evaluation of a mildly pruritic rash present for three months on his trunk, buttocks, and legs (Figure 1). The rash consists of papulosquamous (bumpy, scaly) patches with a symmetrical distribution. A close look at the surface of the patches reveals tiny cracks in the skin, almost like old porcelain, with an orange-pink color. The patient’s skin is quite dry, especially on the trunk and extremities. By obtaining more history, we learned that the patient likes hot showers, especially in the winter, and that he often stays in the shower until the hot water runs out. He uses an antibacterial soap, never moisturizes, and tells us he’s had the same condition each winter for the past several years, but it was never this bad.

I eventually diagnosed asteatotic eczema, a.k.a., eczema craquelé. The condition is quite common, especially during the winter and in older men. The history is quite suggestive of this disorder, particularly the chronicity, but also the long, hot showers and use of fairly harsh soaps. The physical appearance of the condition (tiny fissures and orange-pink color) was also typical.

Looking back on it, I’m puzzled as to why I didn’t just refer to the dermatology books and figure out what it was. But now I realize I was beaten before I had even started because I was doing things out of sequence. I was seeing the patients and then quickly flipping through books to find a match. I didn’t have a differential diagnosis, so I wasn’t looking for the specific features that distinguish this type of eczema from, say, tinea corporis or psoriasis. Furthermore, I hadn’t bothered to read carefully the text accompanying the photos to see how common the problems were, who gets them, or what the differential diagnoses were. In other words, I was trying to get by on the cheap.

Case 2

A 3-year-old girl was referred to me by her pediatrician for evaluation of what he called a “fungal infection” that had not responded to antifungal agents. Present for eight months, this asymptomatic condition was slowly worsening and now involved most of the dorsum of the child’s left foot, with a few lesions extending to her anterior tibial skin. The girl was otherwise healthy. No one else in the family had any similar symptoms. There were no pets in the household and no history of foreign travel.

I couldn’t see much when I first looked at the affected area. I could, however, feel a faint papularity in the skin but detected no scale. What I did next is a critical step in answering the question: “What do I do besides look?” I looked again, but this time I used a different light, shining it across the skin to bring out surface texture highlighted by fine shadows cast by slightly elevated projections. I observed 1- to 3-cm round collections of faint, smooth intradermal papules, creating the illusion of a valleylike indentation (delling) in the centers. I saw a faint suggestion of brownish hyperpigmentation to the lesions but observed no tenderness, edema, or increased warmth.

So, why was this not a fungal infection? First, because there was no history of exposure to a fungus. Fungal infections are contracted through contact with something or someone else. Cats and other children are the most common sources, and neither was present in this case. Moreover, the child was not particularly susceptible (i.e., she was not immunocompromised or immunosuppressed), for example, by steroid therapy. More important, though, was what the lesions did not have—an epidermal component, such as scale. This child’s lesions were intradermal, and dermatophyte infections by definition are superficial and primarily involve the stratum corneum. Failure to respond to appropriate antifungal therapy argued loudly against infection as well.

What I described above is a typical presentation of the fairly common condition granuloma annulare, which has a predilection for the extensor surfaces of the extremities of young females. The lesion also tends to be round (hence the description “annulare”), and the infection is intradermal (never epidermal). The condition tends to be somewhat chronic and asymptomatic, but it is ultimately self-limiting. Granuloma annulare also happens to be quite common. Other diseases should be considered in the differential diagnosis, e.g., sarcoidosis, but the commonality of granuloma annulare suggests that it is the likely culprit, although a biopsy would be definitive.

Flipping through your dermatology book trying to find a match for granuloma annulare-like lesions will get you nowhere. You will have to read about it ahead of time, not only looking carefully at the photos, but reading the text to see how common it is, who is most affected, how the disease can present, and what the differential diagnosis is. Once in a while, running for the dermatology books in the hopes of finding a match enables you to clinch a diagnosis, and this might encourage you to keep doing it that way. This reminds me of the unschooled golfer who hits a green only once in every couple of hundred swings, but this is enough to keep him doing it the same way, his bad habits becoming more firmly entrenched with every swing.

The importance of hands

When I was first learning how to perform physical examinations, I was taught to look first at the hands (dorsa followed by the palms). In the beginning, the only problems I could identify were clubbing and cyanosis. Now I can get a wealth of information by looking at patients’ hands because I examine for specific things and understand their significance. These include such problems as sun damage, Gottron’s papules (distinct lavender, slightly raised patches over the knuckles associated with a serious disease, dermatomyositis) (Figure 3), dilated periungual capillary loops (associated with a number of connective tissue diseases), palmar erythema (associated with pregnancy and alcoholism, among other conditions), hyperlinear palms, nail changes, and more. I see these conditions because I look for them—not merely at them as I used to.

Sir William Osler, described as the father of modern medicine, said it best: “A diagnosis is seldom made if not entertained.” This is no less true for the morphologic and historic features of dermatologic disease. You are not likely to see it if you are not looking for it, because it will not register with your eyes or your brain if it doesn’t have significance.

Think about reading a chest x-ray. As you conduct your systematic exam, you are looking for the presence or absence of findings suggestive of specific disease (e.g., heart size, pleural border, bony structures, mediastinum, effusion, etc.). These are relatively easy to observe because they are anatomic and because the associated diseases are well-known in most cases. One quickly learns to spot radiologic evidence of the common diseases. But even if an obvious lesion is present, most clinicians are taught to immediately leave this and complete the systematic exam. The obvious lesion will still be there when you get back to it.

Before you see the patient

It has to be the same with skin disease. You have to learn about the various conditions, what they look like, how common they are, who is susceptible, and what the differential diagnosis is before you see it on a patient. That way, when you do see it, you’ll be more likely to make the correct diagnosis. And just as with chest films, it’s a classic mistake in dermatology to get caught up in looking at “the lesion in question” and miss more serious disease because a systematic exam was not completed.Another important component of making a dermatologic diagnosis is to look elsewhere on areas of the body not brought to your attention by the patient.

If a patient has a scaly, roundish plaque on the trunk and I suspect psoriasis, I need to corroborate this possible diagnosis with other physical or historic findings. If the patient has psoriasis, it will likely show up elsewhere in predictable locations (i.e., nails, scalp, ears, and intergluteal skin) (Figure 4). In approximately one third of psoriasis cases, patients will confirm a family history of the disease.

“Looking elsewhere” could help diagnose other diseases like erythema multiforme (Figure 5), one of the so-called “reactive erythemas.” Erythema multiforme is notorious in dermatology circles for being triggered by a recent herpes infection in about 50% of cases. It is also fairly common on the palms. Does your patient have an odd palmar rash?

Look for and ask about recurrent herpes. Besides looking elsewhere, clinicians should not forget about obtaining a more detailed patient history. Even though history is less important in assessing skin problems than in most other areas of everyday clinical practice, it still pays to ask questions such as, “Are you ill?” It is amazing how often a patient will be referred to a dermatologist for possible varicella even though he is not the least bit sick.

Other questions to ask include: Have you ever had this before? Is anyone else in your home similarly affected? What do you do for a living? What medications do you take? Have you ever seen a dermatologist for this? What was his/her diagnosis? Do you have any hobbies?

I had a patient tell me she raises tropical fish in her spare time. This immediately raised suspicions that the nonhealing verrucous lesion on her hand might have been caused by the organism Mycobacterium marinum, which can be acquired from fish tanks. Sure enough, cultures confirmed my suspicion.

Mr. Monroe is a physician assistant specializing in dermatology at Warren Clinic in Tulsa, Okla., and founder of the Society of Dermatology Physician Assistants.