Dermoscopy of Lentigo Maligna Melanoma

Report of 125 Cases

P. Pralong; E. Bathelier; S. Dalle; N. Poulalhon; S. Debarbieux; L. Thomas

Disclosures

The British Journal of Dermatology. 2012;167(2):280-287. 

In This Article

Abstract and Introduction

Abstract

Background Lentigo maligna melanoma (LMM) is the most common subtype of melanoma on the face. Its presentation may be quite subtle, particularly in early stages, and delayed diagnosis is common. Few dermoscopic studies have been performed and the main dermoscopic features of LMM were defined by Stolz and coworkers in 2000.
Objectives To investigate classical as well as new dermoscopic features in a large series of LMM in a white-skinned population, in order to evaluate their diagnostic value.
Methods One hundred and twenty-five consecutive histopathology-proven LMMs were analysed retrospectively based on medical records, clinical and dermoscopic photographs by three independent observers for the presence of 19 predefined criteria.
Results At least one of the classical Stolz criteria was present in 87% of cases (hyperpigmented follicular opening, annular-granular pattern, pigmented rhomboidal structures, obliterated hair follicles). Three original criteria were also present at a relatively high frequency: increased density of the vascular network (58%), red rhomboidal structures (40%), target-like patterns (41%). Darkening at dermoscopic examination (when compared with naked-eye examination) was observed in 25% of lesions. Classical dermoscopic features of extrafacial melanoma (atypical pigment network, irregularly distributed globules, dots, streaks and pseudopods) and vertical growth phase-associated dermoscopic criteria (ulceration, blue papular areas and black structureless areas) were rarely seen. A large number of colours, pigmented rhomboidal structures, obliterated hair follicles and red rhomboidal structures were significantly more frequent in invasive LMMs. In contrast, in situ melanomas were more often associated with one or two colours and few distinctive dermoscopic features.
Conclusions We present herein, in a large series of LMM, confirmation of the diagnostic value of the classical Stolz dermoscopic criteria and describe four additional original criteria, mainly vascular. A correlation between the presence of some dermoscopic features and thicker tumoral invasion has also been demonstrated.

Introduction

Lentigo maligna melanoma (LMM) is the most common subtype of melanoma on the face. It occurs in chronically sun-exposed areas, mostly face and neck, less frequently arms, leg and upper trunk. Its incidence is increasing because of higher cumulative exposure to ultraviolet radiation, and it has a peak of incidence in the seventh to eighth decades of life. A preponderance in women and in fair-skinned populations is classically reported. Its presentation may be quite subtle, particularly in early stages, and delayed diagnosis is common. Despite a delay in diagnosis, its prognosis at the time of diagnosis is globally good because of hyperplasia of atypical melanocytes at the basal layer of the epidermis. However, once LMM progresses to the vertical invasive form, its prognosis is similar to that of superficial spreading melanoma when adjusted for tumour thickness.[1–4] Efforts must therefore be made to achieve early diagnosis of LMM, when the lesion to be removed is small and minimally invasive, allowing total excision and a good cosmetic outcome.

In the English language literature, authors refer to the entity as 'lentigo maligna' when it is confined to the epidermis (in situ) and as 'lentigo maligna melanoma' when it invades the dermis. We believe that these two phases refer to the same entity at different stages of development; therefore, in our study we use the same term, LMM, for both noninvasive and invasive forms, naming them 'in situ LMM' and 'invasive LMM', respectively. Dermoscopic features of these two subtypes have been studied together in previously published literature.[5–7]

Recognition and differential diagnosis of facial melanoma is often difficult, particularly at early stages. The well-known 'ABCDE rule' cannot be applied to facial locations.[8] Moreover, naked-eye differential diagnosis may frequently be impaired by the presence of facial solar lentigo that shares the same clinical epidemiological and anatomical characteristics. Dermoscopy has been demonstrated to be an efficient noninvasive technique for the preoperative assessment and positive as well as differential diagnosis of pigmented lesions.[9–11] However, melanocytic lesions on the face – the most common anatomical site for LMM – do not show the classical dermoscopic findings characteristically observed elsewhere on the skin. A conventional pigment network (honeycomb-like pattern) is rarely found: the dermal–epidermal junction of facial skin is flat whereas it is the rete ridge pattern that is optically responsible for the presence of the classical dermoscopic network. In contrast, a pigmented pseudonetwork with broad meshes and holes is created by the numerous, pigment-free, large terminal hair follicles, and photoinduced elastosis is often present. Furthermore, because facial skin is thin and translucent, subtle dermoscopic features like granulation ('peppering') and vascular changes are easily observed.[12,13] For all these reasons, site-specific dermoscopic criteria for melanoma on the face have been described.

Specific dermoscopic patterns for facial LMM have previously been described only by Stolz et al.[7] They have described a 'progression model for lentigo maligna' (Fig. 1), which differentiates four steps of the LMM invasion of the hair follicles observed by dermoscopy. Initially (often irregularly), hyperpigmented follicular openings appear: these features correspond histopathologically to the first visually observable signs of the invasion of the hair shaft by pigmented tumoral melanocytes. Then, fine grey dots and globules appear around the follicles, producing the annular-granular pattern. Next, rhomboid (lozenge-shaped) pigmented areas are formed in the areas located around the hair follicle openings. Lastly, with progression of the malignant cells within all follicular anatomical structures, the hyperpigmentation coalesces, and follicular opening are obliterated. Sensitivity and specificity for these four combined features were 89% and 93%, respectively.[6,7,14]

Figure 1.

The four stages of the 'progression model for lentigo maligna', adapted from Atlas de Dermoscopie:19 (1) hyperpigmented follicular opening; (2) annular-granular pattern; (3) pigmented rhomboidal structures; and (4) obliterated hair follicles.

The aim of the present study was to investigate the classical dermoscopic features of LMM as well as newly observed criteria in a large cohort of patients, including facial and extrafacial LMM, in order to emphasize their diagnostic value.

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