The dermoscopic features of LM-LMM were first described by Schiffner et al.,6 who analyzed 87 pigmented lesions on the face to assess the usefulness of dermoscopy in differentiating LM from solar lentigo and initial seborrheic keratosis. Using univariate analysis, they determined 2 specific features of LM: asymmetric pigmented follicular openings and dark (brown or black) rhomboidal structures. The multivariate logistic regression analysis showed that the combination of 4 features—asymmetric pigmented follicular openings, dark rhomboidal structures, slate-gray dots, and slate-gray globules—had a sensitivity of 89% and a specificity of 96% for the diagnosis of LM. The presence, or absence, of 1 of these features does not reliably indicate a diagnosis of LM, as the features are also found in benign lesions (Table 1). The authors also studied correlations with histologic findings, and proposed a progression growth model for LM. The first feature observed, asymmetric pigmented follicular openings, corresponds to the unequal descent of LM cells in individual hair follicles (Fig. 2A). The next feature is formed by short lines produced by the tumor cells in the epidermis or the upper dermis, which merge to form rhomboidal structures as the lesion advances (Fig. 2B). The slate-gray dots and globules reflect clusters of melanophages in the upper dermis whose distribution around the follicular openings create an annular-granular pattern (Fig. 2C). Finally, the pigmented structures merge to completely obliterate the follicular openings, indicating progression to LMM (Fig. 2D). This pattern may also feature zones with whitish scar-like areas and/or milky-red areas (Fig. 2D).1,4,6

Figure 2.

Dermoscopic features of lentigo maligna. A, Asymmetric pigmented follicular openings (black arrows). B, Lines starting to intersect (white arrows) to form rhomboidal structures (black arrows). C. Gray dots (black arrows) forming a granular-annular pattern and asymmetric pigmented follicular openings (white arrows). D, Homogeneous areas with obliteration of the follicular openings (red arrow) and a whitish scar-like area (white arrow).

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In a later study, Stante et al.7 found that the Schiffner-Stolz criteria (Fig. 3) could be used for the early detection of LM. They described 4 cases of LM lesions measuring up to 5mm with a homogeneous appearance that had been clinically classified as solar lentigos.7 Blanco et al.8 also demonstrated the value of these criteria in a study of 51 LM-LMM lesions, showing that 81% had at least 1 of the 4 features.8

Figure 3.

Lentigo maligna. A, Flat brown symmetric lesion with a diameter of 6mm on the right cheek of an adult. B, Dermoscopic features: asymmetric pigmented follicular openings (black arrows).

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In 2012, Pralong et al.5 described 4 additional dermoscopic criteria for LM-LMM in a study of 125 lesions. Three of the criteria were present in a relatively high proportion of lesions: increased density of the vascular network (found in 58% of lesions), red rhomboidal structures (40%), and target-like patterns (41%). The first feature refers to the observation of a greater density of vessels in the lesion than in the surrounding skin (Fig. 4A). The red rhomboidal structures represent a vascular pattern in the form of a rhomboid around the hair follicles (Fig. 4B). These 2 criteria could be related to tumor neovascularization. The target-like pattern describes a dark dot in the center of a hair follicle with annular hyperpigmentation (Fig. 4C). The fourth criterion, darkening of dermoscopic examination, was observed in 25% of lesions. This feature refers to the fact that the color seen through a dermoscope is darker than that seen in a naked-eye examination (Fig. 4D). Finally, the authors found at least 1 of the 4 classic dermoscopic features in 87% of lesions (a similar proportion to that reported by Ciudad-Blanco et al.8).

Figure 4.

Additional dermoscopic features of lentigo maligna. A, Increased vascular density (black arrows) together with asymmetric pigmented follicular openings and gray dots. B, Red rhomboidal structures (black arrows) and a gray granular-annular pattern. C, Target-like pattern (white arrows) and rhomboidal structures. D, Detection of darker colors in the dermoscopic examination compared with naked-eye inspection (box).

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Although the simultaneous presence of 4 or more classic criteria alone has proven to accurately predict a diagnosis of LM, all of the criteria have a common denominator: the gray color. This color is the result of melanin in the upper dermis or in the hair follicles. It can be observed even before the specific dermoscopic structure has formed, and for Zalaudek and her team, it is the single most sensitive finding for the early detection of LM. Its presence indicates the need for biopsy, even in the case of small lesions (Table 1).1–3 In 1 retrospective study of 201 cases of LM, 88.6% of lesions displayed a gray color.9

LM-LMM can also present as an amelanotic or hypomelanotic lesion. In such cases, dermoscopy may reveal red to pink homogeneous areas or a pseudonetwork, dotted vessels and/or atypical linear vessels, whitish structureless areas, and chrysalis (whitish streaks). Traces of pigment may also be detected. These findings can help to distinguish LM-LMM from other nonpigmented lesions, such as actinic keratosis or superficial squamous cell carcinoma.10

Reflectance confocal microscopy (RCM) is another noninvasive technique that has been found to improve the diagnosis and management of facial LM-LMM. RCM provides real-time images of the epidermis and superficial dermis with a cell-like resolution. Guitera et al.11 created an algorithm for differentiating LM-LMM from other pigmented macules of the face with RCM, and reported sensitivity and specificity rates of 85% and 76%, respectively. This method proved equally useful for diagnosing amelanotic and hypomelanotic lesions.11 However, because of its low availability and longer processing times RCM is generally used to evaluate lesions with equivocal findings by dermoscopy rather than to provide an initial diagnostic evaluation.12 One advantage of RCM is that it performs better than dermoscopy for guiding the selection of the biopsy site for subsequent histologic confirmation. It can also help to delineate surgical margins with greater accuracy prior to surgery,11,12 and has even been successfully used to monitor response to nonsurgical treatment (imiquimod, radiation therapy) in patients in whom surgery is contraindicated.13,14 In 1 study, dermoscopy and RCM were used to detect tumor persistence in 98 LM lesions treated with imiquimod or radiation therapy.14 The inflammation and pigmentation secondary to these treatments make it difficult to detect recurrence. Dermoscopy alone was found to have a sensitivity of 80% and a specificity of just 56%. The criterion that was most closely correlated with treatment failure was the presence of very small brown dots with a granular but not an annular pattern. These dots corresponded to pagetoid cells in the epidermis detected by RCM. While asymmetric pigmented follicular openings was a specific finding (present in 81% of lesions), it was found in just 47% of recurrences. RCM, by contrast, showed a sensitivity of 100% and a specificity of 94% for the detection of recurrence.

Extrafacial LM-LMM is rare, and little has been published about this condition. It is important to differentiate extrafacial LM-LMM from superficial spreading melanoma (SSM) in situ, as they are 2 separate entities, with specific clinical, histologic, and even biologic characteristics. Histologically, LM is characterized by a linear proliferation of atypical melanocytes, with nest formation, along the dermal-epidermal junction and on the walls of the hair follicles and sweat glands, in association with epidermal atrophy and solar elastosis.15 The absence of pagetoid spread of melanocytes in LMM is one of the characteristics that differentiates it from SSM.6 One immunohistochemical study showed that SSM in situ cells have greater proliferative activity and higher rates of angiogenesis than LM cells. These findings are consistent with the biologic behavior of these forms of melanoma, as LM has a longer in situ phase than SSM.16 The architectural differences between facial skin and skin in other locations generated interest in whether the dermoscopic features of extrafacial LM would differ from those of facial LM. Carrera et al.17 described a type of early-stage melanoma on the lower limbs with typical dermoscopic features of facial LM. The 5 lesions had light diffuse pigmentation, together with irregular pigmented follicular openings. The histology study showed that the lesions were in situ melanomas with invasion of the follicles by atypical cells. Lau et al.,15 described 3 cases of extrafacial LM, 2 of which had rhomboidal structures and asymmetric follicular pigmentation. Although the lesions also had features of SSM (irregular dots, projections, and an irregular pigment network), the detection of rhomboidal structures and asymmetric follicular pigmentation suggested a diagnosis of extrafacial LM. The presence of classic features of LM can be explained by the involvement of hair follicles in areas other than the face.15

In a recent study, Jaimes et al.18 analyzed the clinical and dermoscopic features of 186 extrafacial melanomas on chronically sun-damaged skin. The lesions were distinct histologic subtypes of melanoma, the most common of which was LM (40.9%), followed by SSM (22.6%). The most common structures were multiple blue-gray dots (67.7%), lines and/or rhomboidal structures (44.1%), and atypical dots or globules (36.6%). Less common findings were the atypical pigment network (29.6%), asymmetric pigmented follicular openings (27.4%), brown areas without a peripheral structure (24.7%), and scar-like areas (19.9%). The authors described 3 patterns that were present in 78% of cases: pigmented islands (reticular areas or patchy peripheral areas), angulated lines (a term they use to describe lines, rhomboidal structures, and a zig-zag pattern), and a pattern consisting of brown structureless areas and blue-gray dots. LM was the most common histologic subtype associated with each one of these patterns (40%-45%). Limitations of the study were that it was retrospective, the evaluators already knew the diagnosis, and the histological findings were not evaluated.18

Our group studied 5 cases of extrafacial LM-LMM (4 on the upper limbs and 1 on the trunk). In all cases, we observed gray dots forming an annular-granular pattern and light brown structureless areas (Figs. 5 and 6A-D). We observed asymmetric pigmented follicular openings in 1 case (Fig. 5) and rhomboidal structures in 2 (Fig. 6C, D). Our findings are similar to those of previous reports and we agree that dermoscopy could be useful for diagnosing extrafacial LM and distinguishing it from SSM. This obviously has practical implications, as the diagnostic and treatment approaches differ. More and better-designed studies, with analysis of sensitivity and specificity, are needed.

Figure 5.

Extrafacial lentigo maligna. A, Irregular dark brown and black lesion, measuring 2cm at its longest point, in the neckline area. B, Dermoscopic features: asymmetric pigmented follicular openings (black arrows), gray dots forming granular-annular pattern (white arrows), and brown structureless areas.

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Figure 6.

A-D, Dermoscopic features of extrafacial lentigo maligna; lesions located on the upper limbs. Note the gray dots forming a granular-annular pattern in some sectors, the brown structureless areas, and the rhomboidal structures (black arrows). Lesion C is lentigo maligna melanoma; note the whitish-blue veil.

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