Color Critical?

When evaluating skin lesions, it’s clear that both color and structure matter. The common acronym for diagnosing malignant melanoma – ABCDE (asymmetry, borders, colors, diameter, enlarging) – includes both, and dermatologists and pathologists involved in diagnosis are trained to recognize abnormalities in either. But just how much weight each factor carries has been unknown until recently, when the results of a study conducted at the 2014 Memorial Sloan Kettering Cancer Center dermoscopy course were published in JAMA Dermatology (1).

Researchers sought to determine the effect of color images on diagnostic accuracy by showing participants a sample of 40 various skin lesions. Of those, half were shown only once (10 in color and 10 grayscale); the other half were shown twice, once each in color and grayscale. The 158 participants in the study – with an average of six years’ experience evaluating skin lesions and two using dermoscopy – were asked to both provide a diagnosis and rate their confidence level in their conclusion. The results were surprising. When shown unpaired images, univariate analysis suggested that participants were less likely to diagnose color images correctly than grayscale. Multivariate analysis found no association between color images and correct diagnoses. A stratified analysis of paired images further revealed that participants were more likely to diagnose dermatofibroma correctly in grayscale, but squamous cell carcinoma and hemangioma in color.

Overall, the authors concluded that a lesion’s morphological characteristics provide more powerful diagnostic clues than its color. They also proposed teaching dermoscopy to novices using grayscale images in order to emphasize the value of looking at the structures and patterns of lesions. This doesn’t mean that color isn’t an important aspect of the diagnostic evaluation – but next time you’re facing a tricky diagnosis, you may want to look at the image in black and white...