Trichilemmal cyst with homogeneous blue pigmentation on dermoscopy.

A 61-year-old woman was referred to our dermoscopy unit for a pigmented lesion that had been present on her left arm for 8 years. The patient did not notice any enlargement or change in colour. On dermoscopy, homogeneous blue pigmentation was seen. The lesion was excised with the pre-operative diagnosis of melanoma, blue naevus and dermatofibroma. Histopathological examination showed a trichilemmal cyst in the mid-dermis. Although homogeneous blue pigmentation on dermoscopy is the hallmark of blue naevus, it may be seen in metastatic melanoma and exceptionally in hemosiderotic and cellular types of dermatofibroma. Trichilemmal cyst should be borne in mind also in the dermoscopic differential diagnosis.