The significance of blue color in dermatoscopy.

BACKGROUND AND OBJECTIVES: Skin lesions with blue color are frequently excised to rule out malignancy. The objective of the present study was to investigate the significance of blue color.

METHODS: We retrospectively scanned dermatoscopic images for blue color and classified them according to pattern analysis.

RESULTS: Of 1,123 pigmented skin lesions, 144 (12.8 %) showed blue color, 92 of which (63.9 %) were malignant. Among lesions with blue color, the most common benign diagnoses were nevi (n = 35, 24.3 %) and seborrheic keratoses (n = 8, 5.6 %). Of 103 (71.5 %) lesions with a structureless blue pattern, eight (7.8 %) were entirely blue and 95 (92.2 %) were partly blue, of which 81 (78.6 %) showed peripheral or patchy and 14 (13.6 %) central blue color. Most lesions with peripheral or patchy blue color were melanomas (n = 47, 58 %), whereas most lesions with central blue color were nevi (n = 9, 64.3 %). Of 28 lesions with blue clods, 17 (60.7 %) were basal cell carcinomas. With respect to malignancy, the positive predictive value of blue color was 63.9 % (95 % CI: 56.0-71.8 %).

CONCLUSIONS: Among malignant lesions with blue color, structureless peripheral or patchy blue color is a clue for melanoma, while blue clods point to basal cell carcinoma. Pitfalls include seborrheic keratoses, which may show blue color, as well as some nevi, especially combined nevi.