Dermoscopy of Kaposi's sarcoma: Areas exhibiting the multicoloured 'rainbow pattern'

Background  Kaposi's sarcoma is a vascular tumour characterized by a proliferation of spindle cells and endothelial cells to form closely arranged slit-like vascular spaces. Currently, the definitive diagnosis of Kaposi's sarcoma relies on histology. The dermoscopic features of Kaposi's sarcoma are not clearly defined in the scientific literature.
Objectives  We seek to evaluate the dermoscopic features of Kaposi's sarcoma and compare them with other vascular tumours.
Methods  One hundred forty-one lesions from seven patients with histologically proven Kaposi's sarcoma were evaluated using polarized light dermoscopy for the presence of various dermoscopic features. Twenty patients with other vascular tumours were also examined.
Results  Dermoscopic examination revealed bluish-reddish coloration (84% of lesions), multicoloured areas showing various colours of the rainbow spectrum (36%), scaly surface (29%), and small brown globules (15%). The 'rainbow pattern' was found in six out of seven patients with Kaposi's sarcoma and was not observed in other vascular tumours. In addition, there was an absence of dermoscopic features specific for other vascular and non-vascular skin tumours, such as well-defined lacunae or structured vascular pattern, in most of the Kaposi's sarcoma lesions.
Conclusions  The most frequent dermoscopic patterns in Kaposi's sarcoma were found to be bluish-reddish coloration, the 'rainbow pattern', and scaly surface. The rainbow pattern is a dermoscopic feature which has not been previously described. We propose that dermoscopy, as an adjunct to clinical examination, may enhance accuracy in the preoperative diagnosis of Kaposi's sarcoma.