The Role of Color and Morphologic Characteristics in Dermoscopic Diagnosis

Abstract

Importance: Both colors and structures are considered important in the dermoscopic evaluation of skin lesions but their relative significance is unknown.

Objective: To determine if diagnostic accuracy for common skin lesions differs between gray-scale and color dermoscopic images.

Design, setting, and participants: A convenience sample of 40 skin lesions (8 nevi, 8 seborrheic keratoses, 7 basal cell carcinomas, 7 melanomas, 4 hemangiomas, 4 dermatofibromas, 2 squamous cell carcinomas [SCCs]) was selected and shown to attendees of a dermoscopy course (2014 Memorial Sloan Kettering Cancer Center dermoscopy course). Twenty lesions were shown only once, either in gray-scale (n = 10) or color (n = 10) (nonpaired). Twenty lesions were shown twice, once in gray-scale (n = 20) and once in color (n = 20) (paired). Participants provided their diagnosis and confidence level for each of the 60 images. Of the 261 attendees, 158 participated (60.5%) in the study. Most were attending physicians (n = 76 [48.1%]). Most participants were practicing or training in dermatology (n = 144 [91.1%]). The median (interquartile range) experience evaluating skin lesions and using dermoscopy of participants was 6 (13.5) and 2 (4.0) years, respectively.

Main outcomes and measures: Diagnostic accuracy and confidence level of participants evaluating gray-scale and color images. Two separate analyses were performed: (1) an unpaired evaluation comparing gray-scale and color images shown either once or for the first time, and (2) a paired evaluation comparing pairs of gray-scale and color images of the same lesion.

Results: In univariate analysis of unpaired images, color images were less likely to be diagnosed correctly compared with gray-scale images (odds ratio [OR], 0.8; P < .001). Using gray-scale images as the reference, multivariate analyses of both unpaired and paired images found no association between correct lesion diagnosis and use of color images (OR, 1.0; P = .99, and OR, 1.2; P = .82, respectively). Stratified analysis of paired images using a color by diagnosis interaction term showed that participants were more likely to make a correct diagnosis of SCC and hemangioma in color (P < .001 for both comparisons) and dermatofibroma in gray-scale (P < .001).

Conclusions and relevance: Morphologic characteristics (ie, structures and patterns), not color, provide the primary diagnostic clue in dermoscopy. Use of gray-scale images may improve teaching of dermoscopy to novices by emphasizing the evaluation of morphology.

Figure 1. Plot of Predicted Marginal Probabilities of Correct Response for Gray-Scale and Color Image Assessments

A, Unpaired analysis. B, Paired analysis. A color image of squamous cell carcinoma was not included in unpaired image set; thus, there is no corresponding marginal probability of correct response for comparison to the gray-scale image. ^aSignificantly higher or lower scores for color image assessment, in which P < .001.

Figure 2. Examples From Paired Color and Gray-Scale Dermoscopic Images

A and B, Multicolored dermatofibroma; 92.4%of participants correctly diagnosed it in gray-scale compared with 56.9%in color (P < .001). The most common incorrect answer for the color image was melanoma. C and D, the central white lines in this dermatofibroma are more conspicuous in gray-scale in which nearly double the participants were able to render a correct diagnosis (6.5%vs 15.0%, P = .03). E and F, The presence of a blue-white veil in this seborrheic keratosis likely led 44.1%of participants to incorrectly diagnose this as a melanoma. In gray-scale, this lesion was correctly diagnosed by 69.9%of participants (P = .01). G and H, Melanoma in which a nearly equal percentage of participants made the correct diagnosis in both images (85.5%vs. 86.8%, respectively, P = .74).