Lentigo pathology

Histologically, the hallmark of the lentigo (plural lentigines) is an increase in basal melanin. In most forms of lentigo, there is a slightly larger number of melanocytes at basal layer of the epidermis and variable elongation of the challenge ridges

Lentigo simplex

Simple lentigo is common injury and usually appears in childhood. Key features include slight epidermal acanthosis, increased number of evenly dispersed individual melanocytes without atypia in the basal layer and variable basal hyperpigmentation (Figures 1, 2). Occasionally there is scant papillary lymphohistiocytic infiltrate. If the infiltrate includes numerous melanophages Dermoscopic presentation can be atypical.

Lip and genital melanotic macules

the histopathology of lip melanotic macules (appearing on the lips or oral mucous membrane) and vulvar and penile melanotic macules are similar to cutaneous lentigo simplex, however, the acanthosis is less prominent. Dermal melanophages are almost always present and can be a useful diagnostic clue, particularly in subtle oral lesions (figures 3, 4). Differential diagnosis it is post-inflammatory pigmentation.

Lentigo solar

Solar lentigines are benign injuries that occur in the sunexposed skin. Pathogenesis is related to repeated intermittent sun exposure and ultraviolet radiation mutations leading to increased production of melanin and abnormal pigment retention by keratinocytes.

Histologically, there is a noticeable enlargement similar to a bulb of ridge crests that form a lattice pattern due to the interconnections between adjacent strands. This may be less visible in facial lesions. In some cases there is morphological overlap with macular seborrheic keratosis. Basal layer hyperpigmentation may be marked. There is often a slight increase in the number of melanocytes, particularly at the tips of the elongated rete ridges. Solar elastosis usually seen in the dermis (Figure 5).

On facial skin, any significant melanocytic hyperplasia development of a solar lentigo should raise suspicion of an early evolving lentigo maligna: careful search for junctional nesting, attached invasion and nuclear atypia is prudent in all of these cases, and caution should be exercised when reporting partially sampled lesions.

Lichen planus like keratosis

Solar lentigines undergo quite often regression through lichenoid reaction pattern, which may be difficult to distinguish from lichen planus histopathologically. These lesions are often recognizable clinically and dermatoscopically and are known as “lichenoid keratoses” or “lichen planus-like keratoses”. They are most commonly biopsied when clinically confused with superficial basal cells. carcinoma or an atypical melanocytic lesion with a history of change.

inky lentigo

Ink spot lentigines are identified by very dark pigmentation. They appear as irregular black macules often among a series of solar lentigines. Although sometimes clinically alarming, they have a highly characteristic dermoscopy and histology. They show regions of marked basal hyperpigmentation that may alternate with areas of achromatic jump.

Ephelis (freckle)

Ephelides can be easily missed by histopathology. The only finding is a mild basal hypermelanosis.

nail matrix lentigo

Nail matrix lentigines present as greyish-brown longitudinal bands on a nail plate (melanonychia) can be easily missed histopathologically. Basal hypermelanosis is observed. Even a mild hyperplasia of melanocytes with a dendritic morphology should raise the possibility of an atypical melanocytic proliferation or melanoma.

lentiginous nevus

An occasional feature of lentigo simplex is nests of isolated junctional melanocytes. A lentiginous nevus (also called nevoid lentigo or “gingigo”) has few junctional nests and lentiginous melanocytic hyperplasia in the periphery (Figure 6). There may be a continuum along which simple lentigo may evolve to form unions, then compound, and finally intradermal naevi.

lentiginous dysplastic nevus of the elderly

Atypical or lentiginous dysplastic nevus of the elderly is a rather controversial lesion that has probably also been reported as lentiginous melanoma (see below) and Kossard's nevus. The slowly evolving radial growth pattern has led many authors to believe that it represents a low-grade melanoma. These lesions are much more common in New Zealand than those cited in the North American literature, and typically occur on the skin of older adults with chronic sun damage (usually >60 years).

On histology there is a lentiginous proliferation of individual melanocytes in the basal layer, which are of variable density, some areas becoming confluent. Occasional nests are formed. The melanocytes show mild cytologic atypia with hyperchromatic nuclei. Pagetoid spread is often not a prominent feature. Skin changes include focal fibrosis within papillary dermis, pigmentary incontinence and lymphohistiocytic infiltrate. interestingly aggregates of soft melanocytes are frequently present in the superficial dermis (figures 7, 8).

Atypical lentiginous hyperplasia

Pathologists increasingly use the term “atypical lentiginous hyperplasia” to describe lentiginous hyperplasia in which the melanocytes show some cytologic atypia with minimal melanocyte nesting and no melanocytes. flowery pagetoid spread. It is probably not known how many of these are melanoma in the place at a very early stage of evolution. In most cases, it is advisable to manage them surgically with 3-5mm surgical margins to ensure complete removal and/or clinically follow the site.

Differential diagnosis of lentigines

Lentigines must be distinguished clinically and histologically from melanocytic nevi, melanoma, and seborrheic keratoses.