Lentigo maligna
| Lentigo maligna | |
|---|---|
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| Micrograph of lentigo maligna showing the characteristic atypical epidermal melanocytes and solar damage in the superficial dermis. H&E stain. | |
| Classification and external resources | |
| Specialty | oncology, dermatology |
| ICD-10 | C44, D03 (ILDS D03.L10) |
| ICD-O | 8742/2 |
| DiseasesDB | 32059 |
| MeSH | D018327 |
Lentigo maligna (also known as "Lentiginous melanoma on sun-damaged skin") is a melanoma in situ that consists of malignant cells but does not show invasive growth. Lentigo maligna is not the same as lentigo maligna melanoma, and should be discussed separately. It typically progresses very slowly and can remain in a non-invasive form for years. The transition to true melanoma is marked by the appearance of a bumpy surface (itself a marker of vertical growth and invasion), at which point it is called lentigo maligna melanoma. It is normally found in the elderly (peak incidence in the 9th decade), on skin areas with high levels of sun exposure like the face and forearms. Some authors do not consider lentigo maligna to be a melanoma. It is commonly thought of as a melanoma precursor. Incidence of evolution to lentigo maligna melanoma is very low, about 2.2% to 5% in elderly patients.
It is also known as "Hutchinson's melanotic freckle". This is named for Jonathan Hutchinson.
Characteristics include a blue/black stain of skin initially. Skin is thin, about 4-5 cell layers thick, which is often related to aging. Histological features include epidermal atrophy and increased number of melanocytes.
First dilemma in diagnosis is recognition. As lentigo malignas often present on severely sun damaged skin, it is frequently found amongst numerous pigmented lesions - thin seborrheic keratoses, lentigo senilis, lentigines. It is difficult to distinguish these lesions with the naked eye alone, and even with some difficulty using dermatoscopy. As the lentigo maligna is often very large, it often merges with, or encompasses other skin tumors - such as lentigines, melanocytic nevi, and seborrheic keratosis.
Second dilemma is the biopsy technique. Even though excisional biopsy (removing the entire lesion) is ideal, and advocated by pathologists; practical reason dictates that this should not be done. These tumors are often large and presenting on the facial area. Excision of such large tumor would be absolutely contraindicated if the lesion's identity is uncertain. The preferred method of diagnosis is by using a punch biopsy, allowing the physician to sample multiple full thickness pieces of the tumor at multiple sites. While one section of the tumor might show benign melanocytic nevus, another section might show features concerning for severe cellular atypia. When cellular atypia is noted, a pathologist might indicate that the entire lesion should be removed. It is at this point that one can comfortablly remove the entire lesion, and thus confirm the final diagnosis of lentigo maligna. The size of the punch biopsy can vary from 1 mm to 2 mm, but it is preferable to use a punch 1.5 mm or larger. Representative samples of the most atypical parts of the nevus should be biopsied, often guided by dermatoscopy.
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