Dermatology: Practical and Conceptual


Image Letter | Dermatol Pract Concept. 2022;12(3):e2022119 1

Dermatology Practical & Conceptual

Iridescent Changes Observed During  
Dynamic Cross-polarized Dermoscopy

John Paoli1,2, Lykke Barck1,2, Eva Johansson Backman1,2, Ashfaq Marghoob3, Sam Polesie1,2

1 Department of Dermatology and Venereology, Institute of Clinical Sciences, Sahlgrenska Academy, University of Gothenburg, Gothenburg, 

Sweden

2 Region Västra Götaland, Sahlgrenska University Hospital, Department of Dermatology and Venereology, Gothenburg, Sweden

3 Department of Dermatology, Memorial Sloan Kettering Cancer Center, New York, NY, USA

Citation: Paoli J, Barck L, Backman EJ, Marghoob A, Polesie S. Iridescent changes observed during dynamic cross-polarized dermoscopy. 
Dermatol Pract Concept. 2022;12(3):e2022119. DOI: https://doi.org/10.5826/dpc.1203a119

Accepted: November 24, 2021; Published: July 2022

Copyright: ©2022 Paoli et al. This is an open-access article distributed under the terms of the Creative Commons Attribution-
NonCommercial License (BY-NC-4.0), https://creativecommons.org/licenses/by-nc/4.0/, which permits unrestricted noncommercial use, 
distribution, and reproduction in any medium, provided the original authors and source are credited.

Funding: None.

Competing interests: None.

Authorship: All authors have contributed significantly to this publication

Corresponding author: John Paoli, M.D., Ph.D, Department of Dermatology and Venereology, Sahlgrenska University Hospital, Institute of 
Clinical Sciences, Sahlgrenska Academy, University of Gothenburg, Gröna Stråket 16, 413 45, Gothenburg, Sweden Tel: +46(0) 730 40 40 44,  
E-mail: john.paoli@gu.se

Case Presentation 

A 60-year-old male with skin phototype IV from Africa and 

a history of Kaposi sarcoma on his foot presented with a 

rapidly growing, 6.5-mm, bluish-purple nodule on his back. 

Cross-polarized dermoscopy using a DermLite DL4 (3Gen) 

coupled with an iPhone XS Max (Apple) revealed a ‘rainbow 

pattern’ on a structureless red background. By rotating the 

dermoscope without moving the smartphone during imaging, 

also known as dynamic cross-polarized dermoscopy, the color 

distribution within the rainbow pattern changed substantially 

(Figure 1, Supplementary Video 1). The lesion was excised 

and histopathologically confirmed as Kaposi sarcoma.

Teaching point

The metaphoric term ‘rainbow pattern’ is used to describe 

polychromatic structureless areas only seen with polarized 

dermoscopy. It has been described in several different skin 

tumors (eg Kaposi sarcoma, hemosiderotic dermatofibroma, 

angiokeratoma, aneurysmal atypical fibroxanthoma, mela-

noma and basal cell carcinoma) and other skin conditions 

(eg stasis dermatitis, lichen planus and scars) [1]. It is sur-

mised that polarized light passing through slits created by 

parallelly aligned collagen bundles or vessels may cause the 

light to separate into different wavelengths [2]. Although 

the exact structures that actually cause the optical interfer-

ence are unknown, the observed phenomenon is called iri-

descence. By applying dynamic cross-polarized dermoscopy, 

we demonstrate that the iridescence changes with the angle 

of polarization. This angular dependence of cross-polarized 

light has also been demonstrated previously by Marghoob 

et al on shiny white lines, which are only visible with the 

dermoscope positioned at specific angles.



2 Image Letter | Dermatol Pract Concept. 2022;12(3):e2022119

References

1. Elmas OF, Mayisoglu H, Celik M, Kilitci A, Akdeniz N. Dermo-

scopic rainbow pattern: A strong clue to malignancy or just a light 

show? North Clin Istanb. 2020;7(5):494–498. DOI: 10.14744/

nci.2020.32656. PMID: 33163886. PMCID: PMC7603844.

2. Draghici C, Vajaitu C, Solomon I, Voiculescu VM, Popa MI, 

Lupu M. The Dermoscopic Rainbow Pattern - A Review of the 

Literature. Acta Dermatovenerol Croat. 2019;27(2):111–115. 

PMID: 31351506.

Figure 1. (A) Clinical presentation of a case of Kaposi sarcoma. (B) Iridescence or ‘rainbow pattern’ observed during cross-polarized 

dermoscopy at a specific angle. (C) Modified iridescence shown after rotating the dermoscope 90°.

Supplementary Video Legend

Supplementary Video 1. The iridescence or ‘rainbow pat-

tern’ changes substantially while rotating the dermoscope 

relative to the smartphone camera (dynamic cross-polarized 

dermoscopy), thus demonstrating the angular dependence of 

polarization.

https://mattiolihealth.com/wp-content/uploads/2022/08/dp1203a119s1.mp4