Dermoscopic rainbow pattern: A strong clue to malignancy or just a light show?

Rainbow pattern is a dermoscopic finding composed of multiple colors simulating a rainbow. It is known as a characteristic feature of Kaposi's sarcoma. Here, we reported different non-Kaposi's sarcoma conditions with a rainbow pattern aiming to discuss the diagnostic significance of the finding.

In this multicenter study, dermoscopic images of the non-Kaposi's sarcoma lesions having a histopathological diagnosis were reviewed for the presence of a rainbow pattern. Dermoscopic examination was performed by a polarized handheld dermoscope with x10 magnification.

A total of 840 lesions were reviewed and 21 (2%) non-Kaposi sarcoma lesions having dermoscopic rainbow pattern were detected. These lesions were as follows; pyogenic granuloma (n=4, 19%), hypertrophic scar (n=4, 19%), basal cell carcinoma (n=2, 10%), dermatofibroma (n=2, 10%), angiokeratoma (n=2, 10%), blue nevus (n=1, 5%), granuloma annulare (n=1, 5%), strawberry angioma (n=1, 5%), epidermal cyst (n=1, 5%), malignant melanoma (n=1, 5%), dissecting cellulitis (n=1, 5%) and subungual hematoma (n=1, 5%). The most common localization was limb (n=14, 67%) followed by face (n=3, 14%).

We suggest that the rainbow pattern is a complex and quite unspecific optic phenomenon which can be seen both in vascular and non-vascular lesions. Its diagnostic significance should be considered in the context of the other structural dermoscopic finding. To the best of our knowledge, to our knowledge, this is the most comprehensive study focusing on rainbow pattern in non-Kaposi's sarcoma lesions. Here, we also reported rainbow pattern in dissecting cellulitis, granuloma annulare and subungual hematoma which has not been shown to have rainbow pattern previously.