Folliculotropism in pigmented facial macules: Differential diagnosis with reflectance confocal microscopy

Abstract

Pigmented facial macules are common on sun damage skin. The diagnosis of early stage lentigo maligna (LM) and lentigo maligna melanoma (LMM) is challenging. Reflectance confocal microscopy (RCM) has been proven to increase diagnostic accuracy of facial lesions. A total of 154 pigmented facial macules, retrospectively collected, were evaluated for the presence of already‐described RCM features and new parameters depicting aspects of the follicle. Melanocytic nests, roundish pagetoid cells, follicular infiltration, bulgings from the follicles and many bright dendrites and infiltration of the hair follicle (ie, folliculotropism) were found to be indicative of LM/LMM compared to non‐melanocytic skin neoplasms (NMSNs), with an overall sensitivity of 96% and specificity of 83%. Concerning NMSNs, solar lentigo and lichen planus‐like keratosis resulted better distinguishable from LM/LMM because usually lacking malignant features and presenting characteristic diagnostic parameters, such as epidermal cobblestone pattern and polycyclic papillary contours. On the other hand, distinction of pigmented actinic keratosis (PAK) resulted more difficult, and needing evaluation of hair follicle infiltration and bulging structures, due to the frequent observation of few bright dendrites in the epidermis, but predominantly not infiltrating the hair follicle (estimated specificity for PAK 53%). A detailed evaluation of the components of the folliculotropism may help to improve the diagnostic accuracy. The classification of the type, distribution and amount of cells, and the presence of bulging around the follicles seem to represent important tools for the differentiation between PAK and LM/LMM at RCM analysis.

Diagnostic impact of reflectance confocal microscopy as a second‐level examination for facial skin lesions

“…RCM of upper epidermal layers (approximately 1 mm x 1 mm field of view) shows loss of the regular epidermal architecture due to presence of large, bright, round and dendritic pagetoid cells (arrows) as well as sheets of dendrites (c; arrowhead). At the DEJ (approximately 1 mm x 1 mm field of view), there are bright dendrites (arrowhead) and tubular cell nests of various reflectivities (arrows) in irregularly shaped rete ridges with abrupt endings, also referred to as “medusa head‐like structures” or “irregular meshwork pattern” at the DEJ ; outlines of single cells are occasionally observed within the nests. These RCM findings are consistent with lentigo maligna (d).…”

Challenging facial pigmented lesions: values and limits of confocal microscopy

“…Moreover, the presence in lesion C of perifollicular inflammatory cells and Langerhans cells, resembling dendritic melanocytes in RCM, represents a possible RCM pitfall in the differentiation of PFL ( Figure 2D ). A detailed evaluation of the components of the folliculotropism in facial macules may help to improve the diagnostic accuracy of RCM findings [ 3 ]. The infiltration of the hair follicle was found to be indicative of LM/LMM compared to nonmelanocytic skin neoplasms, with an overall sensitivity of 96% and specificity of 83% [ 3 ].…”

“…A detailed evaluation of the components of the folliculotropism in facial macules may help to improve the diagnostic accuracy of RCM findings [ 3 ]. The infiltration of the hair follicle was found to be indicative of LM/LMM compared to nonmelanocytic skin neoplasms, with an overall sensitivity of 96% and specificity of 83% [ 3 ]. A few bright dendrites in the epidermis, but not infiltrating the hair follicle predominantly, have estimated specificity for pigmented actinic keratosis (53%) [ 3 ].…”

Diagnostischer Nutzen der Konfokalmikroskopie als weiterführende Untersuchungsmethode von Gesichtsläsionen

“…An der DEJ (ca. 1 × 1 mm Gesichtsfeld) finden sich helle Dendriten (Pfeilspitze) und tubuläre Zellnester unterschiedlicher Reflektivität (Pfeile) in irregulär geformten und abrupt endenden Reteleisten, auch als „Medusakopf‐artige Strukturen“ oder „irreguläres Geflecht“ an der DEJ beschrieben ; Einzelzellen können zum Teil innerhalb der Nester abgegrenzt werden. Diese RCM‐Befunde sind mit einer Lentigo maligna vereinbar (d).…”