Diagnosing melanoma in situ
SOLAR lentigines are usually a uniform colour with a well-defined edge.
However, in lentigo maligna the colour is usually darker and variable and the lesion edges sharper. This is because there is an abnormal proliferation of atypical melanocytes at the dermo-epidermal junction, giving more pigment and sharp edges as the cells proliferate.
In a solar lentigo the melanocytes are in normal numbers and the pigment they produce is distributed evenly to the keratinocytes. Lentigo maligna is really melanoma in situ. The atypical melanocytes are