Lentigo Maligna
Definition: Lentigo maligna (LM), also known as Hutchinson melanotic freckle, is a slow-growing precursor of lentigo maligna melanoma (LMM). LM often occurs in sun-damaged skin of the head and neck region, usually in the elderly.
Etiology: LM occurs due to the proliferation of malignant melanocytes within the hair follicle and the basal layer of the epidermis. Solar damage to the skin results in the abnormal melanocytes proliferating unchecked. Major risk factors for LM include cumulative lifetime UVR exposure, x-ray radiation, estrogen/progesterone therapy, nonpermanent hair dyes and genetic conditions predisposing to sun sensitivity. UVR exposure causes oxidative damage which affects genes involved in KIT CCND1, MITF, NRAS, and p53 pathways.
Epidemiology: LM is the precursor to the third most common subtype of melanoma (LMM), comprising up to 15% of all melanomas and up to 26% of melanomas on the head and neck. Women are often more affected by LM than men, with the ratio being 1.7: 1. LM occurs often in those with very fair skin (Fitzpatrick types 1,2), and is rare in brown or black skin (Fitzpatrick types 4,5,6). LM is more common in males, and the mean age of diagnosis is between 66- 72 years.
Signs: LM is slow-growing and may resemble a lentigo in its early stages. Over several years it may develop the following characteristics: smooth, flat surface, size >6 mm and irregular shape with variable pigmentation ranging from light brown, tan, dark brown, pink, red or white. 86% of LM lesions occur on the head and neck, with a predilection for the cheek. Extrafacial lesions may be seen on the extremities of women and the back in men.
Symptoms: LM lesions are usually asymptomatic. In 3-10% of cases, invasive melanoma may arise from LM in which symptoms include thickened portions of the lesion, increasing number of colours, ulceration, bleeding, itching or stinging.
Differentials: Solar lentigo, Melanocytic naevi, seborrheic keratosis, lichen planus-like keratosis, and pigmented actinic keratosis
Diagnosis: The clinical diagnosis of LM is by dermoscopy or confocal microscopy. If a lesion if suspicious of LM, an excisional biopsy is indicated for histopathological diagnosis.
Treatment: The treatment of choice is surgical excision. For poor surgical candidates, radiotherapy, or a topical imiquimod 5% cream may be indicated.
References:
- Oakley A. Lentigo maligna and lentigo maligna melanoma | DermNet NZ. dermnetnz.org. Published 2011. https://dermnetnz.org/topics/lentigo-maligna-and-lentigo-maligna-melanoma
- Xiong M, Charifa A, Chen CSJ. Lentigo Maligna Melanoma. In: StatPearls. Treasure Island (FL): StatPearls Publishing; October 31, 2022.