Lentigo Maligna and Lentigo Maligna Melanoma

01The LM progression model articulates four sequential dermoscopic features. First, gray dots (corresponding to single melanocytes or melanin within macrophages) develop as the earliest sign. Second, the dots aggregate into gray globules. Third, asymmetrically pigmented follicular openings appear as the proliferation invades the hair follicle epithelium. Fourth, rhomboidal structures (gray-brown lines that connect pigmented follicles into polygonal patterns) develop as confluent perifollicular pigment forms quadrilateral connections. In late LM and LMM, follicular openings are obliterated by pigment, blue-white veil and atypical vessels appear, and the lesion enters vertical-growth phase.

02Annular-granular pattern describes confluent gray dots arranged in a ring around follicular openings. This pattern is the dermoscopic equivalent of single-cell melanocyte proliferation along the rete ridges with melanin uptake by upper-dermal macrophages. It is classically described in LM but overlaps with pigmented actinic keratosis and pigmented solar lentigo, making it sensitive but not specific.

03Asymmetrically pigmented follicular openings are arguably the most specific LM feature. A normal follicular opening on facial skin shows a small pigment ring of uniform thickness or no pigment at all. In LM the ring becomes asymmetric, thicker on one side, sometimes with pigment extending into the follicular ostium. The hypothesis that LM may originate from cancer stem cells of the hair-follicle bulge rather than from epidermal melanocytes is consistent with this folliculocentric pattern.

04Rhomboidal structures (also called rhomboid lines or polygons) are gray-brown lines connecting pigmented follicular openings into quadrilateral or polygonal shapes. They reflect confluent perifollicular and interfollicular junctional melanocytic proliferation. Lallas's multicenter study identified gray rhomboidal lines as the single strongest dermoscopic predictor of LM (sixfold odds) but only present in 56% of LMs, so their absence does not exclude diagnosis.

05Gray circles (small gray rings within follicular openings) and gray peppering (annular granular dots) are the early features that may appear before rhomboidal structures form. Tschandl identified gray circles as the most specific isolated LM finding. In Lallas's analysis, grey circles posed a 5.9-fold univariate increased probability of LM, though the multivariate model favored rhomboidal lines.

06The target-like pattern describes a follicular opening with a central dark dot or globule surrounded by a brown halo, sometimes with an outer gray ring. It represents pigment within the follicular ostium plus perifollicular pigment. This pattern is uncommon but quite specific for LM when distinguishable from the targetoid follicles of PAK (which have central yellow keratotic plug and white outer halo).

07Reflectance confocal microscopy (RCM) correlates with dermoscopic features. Pagetoid round cells around follicles correspond to gray circles, atypical junctional thickening corresponds to rhomboidal structures, and dermal melanophages correspond to gray peppering. RCM raises diagnostic accuracy when added to dermoscopy and is increasingly used to map LM borders preoperatively.

08Lentigo maligna borders are notoriously difficult to delineate clinically. Surgical management therefore relies on staged excision techniques. Mohs micrographic surgery with rush permanent sections (square procedure or slow Mohs) allows comprehensive peripheral evaluation while overcoming the difficulty of identifying single atypical melanocytes on frozen sections. MART-1 (Melan-A) immunohistochemistry on permanent sections is now the standard adjunct, dramatically improving sensitivity for residual atypical melanocytes at the surgical margin compared with H&E alone.

09Desmoplastic melanoma represents a distinct LMM subtype that is often amelanotic or hypomelanotic. The lesions appear as scar-like indurated plaques on chronically sun-damaged skin, with a male predominance (1.75:1) and a mean Breslow thickness around 3.7 mm in Pampena's systematic review. Dermoscopically, white shiny streaks, milky-red areas, regression structures, and atypical polymorphic and linear-irregular vessels dominate. Desmoplastic melanoma has higher local recurrence rates and distinct staging considerations (lower sentinel-lymph-node positivity in pure desmoplastic lesions).