Description: Close up showing the basal layer pigmentation

History:

 This lesion looked darker than the many other seborrhoeic keratoses on this elderly man's back. It was thought there might be a lentiginous proliferation of atypical melanocytes in the lesion . Also the multiple colours and the white lines were unusual for a seborrhoeic keratosis. However pathology of a large shave biopsy excision showed only a pigmented thick seborrhoeic keratosis with increased pigment in normal basal keratinocytes. The blue colour was because of the depth of the lesion ie thick. No idea why the white lines!

View the video of the pathology here.