Lentigo Maligna – Not Always a Face and Neck Disease of the Elderly

Lentigo maligna (LM) is relatively rare form of malignant melanoma (MM), corresponding to 4–15% of all MM cases [1]. LM usually occurs in sun-damaged skin and is typically poorly circumscribed; its diagnosis is based on atypical junctional melanocytic hyperplasia combined with solar elastosis and epidermal atrophy [1, 2]. When LM invades the dermis, it is called lentigo maligna melanoma (LMM). The exact percentage of LM evolving to LMM is not clear, varying from 5 to 50% [1, 3].

LM occurs almost exclusively in middle-aged and elderly Caucasians [2]; its incidence is increasing because of a higher cumulative exposure to ultraviolet radiation [4]. Classically, LM presents as a slowly enlarging patch with variable color and with ill-defined borders, most frequently located on the head and neck (86%), with predilection for the cheeks [5].

The clinical presentation may be subtle, particularly in early stages, and therefore, delayed diagnosis is common [4]. Because of its potential significant subclinical extension, LM has a higher risk of local recurrence than other types of correctly treated melanoma. Once LM progresses to its vertically invasive form, its prognosis is similar to that of other types of MM. The diagnosis is a challenge in most cases. Suspicious lesions should undergo dermoscopic evaluation that may contribute to an early diagnosis [6].

The aim of this study was to characterize the clinical and dermoscopic features of LM/LMM in our center during the last decade.

For further details, see the online supplementary material (see www.karger.com/doi/10.1159/000489397 for all online suppl. material) (Fig. 1).

Over the assessed 10-year period, we observed a total of 21 LM (out of 152 melanomas observed within the same period), of which 12 had an extrafacial location. Half of the latter were located on the upper limbs (upper arm: n = 3; forearm: n = 2; hand: n = 1; Fig. 2), followed by the lower limbs (lower leg: n = 4; thigh: n = 1) and the upper back (n = 1). In all patients, LM was first suspected by a dermatologist. The median age at diagnosis was 63 years (ranging from 38 to 84 years).

Most LM cases were female (16/21) and occurred in patients with phototype II (13/21) and less than 25 nevi (13/21) (Table 1). More than half of the patients (11/21) had a history of a skin neoplasm or actinic keratosis. The median diameter for the assessed LM was 6 mm (interquartile range, IQR = 4.5 mm – ranging from 1 to 15 mm), corresponding to a median diameter of 5.1 mm among females (IQR = 5.3 mm) and 8.0 mm among males (IQR = 2.5 mm).

Of the “ABCD” signs, asymmetry, irregular border and diameter ≥5 mm were observed in more than half of the neoplasms; however, the presence of at least 3 ABCD signs was only present in 2 out of 6 cases of LM with diameter < 5 mm (Table 2). The most common dermoscopic findings were atypical pigment network (11/20), dis-appearance of follicular structures (7/20) and multicomponent pattern (7/20) (Table 1). Five lesions were inva sive – LMM – all of them staged as Clark level II, having a median Breslow depth of 0.2 mm (IQR = 0.1 mm).

Facial LM were observed for half of the female patients (8/16) but for only one fifth (1/5) of male patients. Results of the comparisons between facial versus extrafacial LM, and between neoplasms of < 5 versus ≥5 mm diameter are presented in Table 1 and Table 2, respectively.

Despite being a small retrospective series of a single center, this study has some interesting results, particularly regarding the location and median diameter of the assessed neoplasm, as well as the patients’ median age.

In fact, in our study, almost 60% of LM were located outside the face and neck. Extrafacial location had been reported by previous studies, but never to such an extent. In most studies, LM involving the head and neck accounted for 75–85%, and only 15–25% were outside the face and neck. Patient age and gender distribution were also surprisingly different from those usually described in the literature [5, 7] in this study, the median age was lower than usually reported (63 vs. 70–75 years) [7]. In addition, more than three quarters of our patients were female, while most previous studies had reported LM to be more common among males [5, 7].

Changing patterns of sun exposure may contribute to the changing epidemiology of LM. The face is consistently more exposed than other areas, but the relationship between sun exposure and LM/LMM might be complex. The regular use of sunscreens on the face may not totally explain the higher incidence of extrafacial lesions, because females typically use more sunscreen all over the year than males (among whom we only found 1 facial lesion).

The median diameter at diagnosis was very small (median of 6 mm; 9 lesions with ≤5 mm). The bigger lesion observed had 15 mm and was smaller than the mean diameter found in a Spanish study (15.8 mm) [7]. Females had a smaller median diameter than males, suggesting a more delayed diagnosis among the latter.

Although the “ABCD” criteria have a good semiological value in the differential diagnosis of pigmented lesions [8], in this study only 2 cases of LM < 5 mm had 3 signs of this rule, which does therefore not seem to be useful for the diagnosis of early small lesions.

Dermoscopy of facial pigmented lesions has been widely studied [4, 9, 10]. In our series, the most frequent feature for facial LM (particularly in lesions ≥5 mm) were disappearance of follicular structures, annular granular pattern and irregular follicular pigmentation, but also multicomponent pattern. Dermoscopic features of extrafacial LM include a combination of features of facial LM and in situ superficial spreading MM [9]. None of the extrafacial cases of this series had a single feature of facial LM. Curiously, only 1 case of angulated lines was found; it concerned a facial LM, and not an extrafacial lesion, where this pattern has been previously reported [11].

Reflectance confocal microscopy has been described as an important complementary tool for diagnosis, treatment guidance and follow-up of LM [12, 13], but it is a time-consuming and highly costly technique. Although more sensitive, it is less specific for the diagnosis of LM [14].

A routine full-body examination of the patients, and a regular photographic documentation with dermoscopy [15], associated with higher suspicions on patients with photo damage or a skin cancer history, may justify the small diameter of the lesions in this study. Clinical suspicion supported by complete history and close inspection assisted by dermoscopy are of most importance to recognize early LM.

60% of lentigo maligna are located in photo-exposed areas outside the head and neck.

Subjects have given their informed consent for the study.

The authors have no conflict of interest to declare.

60% of lentigo maligna are located in photo-exposed areas outside the head and neck.