Lentigo Maligna Melanoma

Marti Jill Rothe, MD

Recurring blisters on the sides of the fingers brought a 72-year-old man to his physician. He was asked to change into a gown for a full-skin examination. Physical examination demonstrated minute papulovesicles affecting the medial and lateral aspects of the fingers, consistent with dyshidrosis. The patient's skin was severely sun-damaged, and there was an irregularly pigmented, asymmetric patch affecting the posterolateral neck.

Recurring blisters on the sides of the fingers brought a 72-year-old man to his physician. He was asked to change into a gown for a full-skin examination. Physical examination demonstrated minute papulovesicles affecting the medial and lateral aspects of the fingers, consistent with dyshidrosis. The patient's skin was severely sun-damaged, and there was an irregularly pigmented, asymmetric patch affecting the posterolateral neck, as seen in the Figure. A 4-mm punch biopsy of the deeply pigmented superior aspect of the lesion was performed.

Pathology studies showed a broad and asymmetric lesion with poorly demarcated margins. The epidermis was thin, with some areas of large, vacuolated or pagetoid cells. Single cells predominated over nests of cells. The upper dermis showed marked solar elastosis and an inflammatory infiltrate. The features were consistent with lentigo maligna melanoma.

This form of melanoma occurs on chronically sun-damaged skin, particularly in elderly persons; it is especially common in the head and neck region

The lesion usually appears as an irregularly shaped, variably pigmented, asymmetric patch. Small, deeply pigmented nodules or flat papules may appear superimposed on the pigmented patch.

The clinical differential diagnosis of lentigo maligna melanoma includes solar lentigo, pigmented actinic keratosis, and pigmented Bowen's disease. A key to the diagnosis of lentigo maligna melanoma is the asymmetric, variegated pigmentation, which is generally not seen in solar lentigines. Lentigo maligna melanoma is marked by slow peripheral growth (“radial growth phase") over a period of years. Tan or light brown macular portions of the lesion show increased numbers of melanocytes; these may appear normal or severely atypical; deeply pigmented papular or nodular portions of the lesion show nested atypical melanocytes.

Treatment is surgical excision with margins appropriate for the depth of invasion. Wide margins may be difficult to obtain in instances of a very broad lesion in a cosmetically vulnerable site on the face. Referral to a dermatologist is appropriate when the borders of the lesion are not clear-cut and before extensive surgery is undertaken. The prognosis correlates well with tumor thickness; these lesions are usually thin and thus have a better prognosis than deeper tumors.