When history overrides the dermatoscope

There is a temptation, once you have learned dermoscopy, to let the dermatoscope have the final word. It is a powerful tool and it often provides clarity. But there are specific situations where clinical history should override a reassuring dermoscopic appearance.

The featureless nodule

Amelanotic melanoma is the most important lesson in the limits of dermoscopy. Because it lacks significant pigment, it may show few or none of the classic dermoscopic features of melanoma. It can appear as a pink, featureless nodule. The dermatoscope may show non-specific vascular patterns but nothing that shouts "melanoma."

In these cases, the history saves you. A rapidly growing pink nodule in a sun-exposed area, in a patient with risk factors, is concerning regardless of what the dermatoscope shows.

The changing lesion in a stable field

A patient with many stable naevi presents with one lesion that has changed. Even if the dermoscopic features of the changed lesion do not look classically malignant, the fact that it is behaving differently from all its neighbours is significant. The ugly duckling sign works at the level of history as well as appearance.

The patient who keeps coming back

If a patient returns with ongoing concern about a lesion you previously assessed as benign, consider whether referral is now appropriate. Persistent patient concern, even without obvious interval change, is a safety-net trigger. It may be that the patient is noticing subtle changes that are not yet apparent on dermoscopy, or it may be that reassurance is not possible without specialist confirmation.

Either way, the cost of a referral is low compared to the cost of a missed diagnosis.

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