Also known as Hutchinson's Premelanotic Freckle, Lentigo Maligna [LM] is a precancerous freckle that can progress to melanoma which is a potentially serious and life-threatening skin cancer.
It is slow growing and usually has a long growth phase staying precanerous for years before progressing through peripheral extension until a raised central nodule of cancerous cell called melanoma arises. This is now a lentigo maligna melanoma (LMM).
It occurs commonly on the face of the elderly
Lentigo maligna Wikipedia
emedicine lentigo maligna
The emedicine article says that the lifetime risk of turning to melanoma is considered to be 5% if the LM is diagnosed at age 45
||Wide local excision with 5 mm margin
||Johnsons square procedure
This is mostly and usually treated surgically with an excision margin of 5 mm.
Sometimes incomplete excision occurs because of cells that are observed after excision by the pathologist under the microscope during histology and which can't be seen clinically. Sometimes the LM can be without colour [amelanotic] which makes assessment of how much to cut out difficult.
Johnson's square procedure is a technique I learnt in the U.S. during my fellowship and brought back and started in Nottingham. Our experience which is probably the widest in the UK was reported in the literature as
Patel A, Perkins W, Leach I, Varma S. Johnsons square procedure for lentigo maligna and lentigo maligna melanoma. Clin Exp Dermatol 2014; 39: 570-6
Currently this is used for incompletely excised LM or for those where margins are very indistinct.
Surgery however can cause a lot of scarring and treatment with imquimod 3x /w for 6 weeks sometimes with an additional 5x/w for 4 weeks may be an effective long term strategy that might avoid disfiguring surgery. [Kai AC et al. Five year recurrence rate of lentigo maligna after treatment with imiquimod. BJD 2016; 174: 165-8]. In this study 40 patients had imiquimod. 11/40 had residual LM. Long term success appears to be 66.7%.
NICE 2015 says
Consider where unacceptable disfigurement or morbidity.