When skin lesions don't follow the rules, dig deeper
Most skin lesions encountered by experienced dermatoscopists can be effortlessly recognised as falling into one of five benign categories: naevus; benign keratinocytic (for example, seborrhoeic keratosis); haemangioma; dermatofibroma; and sebaceous gland hyperplasia.
This ability requires basic training in dermatoscopy followed by the deliberate examination of apparently normal lesions.
Pattern analysis can then be reserved for those lesions that cannot be categorised into one of the five benign groups, and it is useful to have a structured approach in such situations.
All published algorithms for the diagnosis of pigmented skin lesions are based on the chaotic behaviour of malignant tissue that has broken free of normal constraints.
This commonly causes asymmetry of any or all of pattern, colour, and border-abruptness, which can cause the lesion to break the pattern of surrounding lesions, both