Key points in dermoscopic differentiation between lentigo maligna and solar lentigo

Abstract

A clinical diagnosis of lentigo maligna at an early stage is often difficult even for experienced dermatologists. Differential diagnoses would include solar lentigo, early lesions of seborrheic keratosis, lichen planus-like keratosis, pigmented actinic keratosis and melanocytic nevus. Dermoscopy has been shown to have higher diagnostic accuracy, especially in the diagnosis of pigmented skin lesions, in the past two decades. To aim of the present study was to review the diagnostic key points on dermoscopy in the published work to differentiate lentigo maligna from other differential diagnoses and reassess these important features on dermoscopy for specificity by describing the findings in detail. Diagnostic key points for lentigo maligna/lentigo maligna melanoma on dermoscopy are asymmetrical pigmented follicular openings, rhomboidal structures, annular-granular structures and gray pseudo-network. Lentigo maligna, at first, seems to occur as asymmetrical pigmented follicular openings and/or annular-granular structures, then expand and develop into the rhomboidal structures. Annular-granular structures and gray pseudo-network seem to be observed also in regressive areas of solar lentigo/initial seborrheic keratosis, lichen planus-like keratosis and pigmented actinic keratosis. The four important criteria on dermoscopy for the diagnosis of lentigo maligna have been reviewed, and the former two criteria seem to be more specific, but it might be difficult to recognize these findings without misinterpretation. The latter two seem to be not so specific as they would also be demonstrated in other pigmented epidermal lesions, although the distribution of the structures in these disorders would be inclined to be more homogeneous than that of lentigo maligna.

Unstable solar lentigo: A defined separate entity

“…These field cells were interpreted as subtle surrounding melanoma in situ. Whether or not unstable lentigines can evolve into LM, we routinely encounter solar lentigo and unstable solar lentigo at the edge of LM (Figs 4,5). Similar studies on lentigo maligna and surrounding unstable solar lentigo would be of interest.…”

“…7 Dermoscopy of lentigo maligna demonstrates characteristic features, including atypical pseudo-networks, asymmetrical pigmented follicular openings, rhomboidal structures, annular or granular structures and a grey pseudo-network. 5 …”

“…The surface may be rough on palpation and dermoscopically there may be comedo-like openings, as these lesions are often in the process of evolving into seborrhoeic keratoses. 5 The unstable solar lentigo typically presents as an isolated, irregularly pigmented macule on a background of solar damage (Fig. 1).…”

Staged margin‐controlled excision (SMEX) for lentigo maligna melanoma in situ

“…Also, a protocol for inking and histopathological assessment of all margin strips and final excision was developed, so that the same pathological assessment could be applied repeatedly to all cases. Pre‐operatively, each patient underwent evaluation of the lesion with Wood's lamp and/or dermoscopy in order to best evaluate the tumor margins . The lesion was outlined with surgical ink in a circular or oval configuration (avoiding notches and indentations in the tumor contour).…”

Does it look like melanoma? A pilot study of the effect of sunless tanning on dermoscopy of pigmented skin lesions

“…4,5 In skin areas such as the face, which are exposed to high, accumulated doses of UVR, development of lentigo maligna (LM) and LM melanoma (LMM) can occur. 7,8 The use of self-tanning products containing dihydroxyacetone (DHA) could potentially decrease UVR exposure in the population, 9,10 which might lead to a decrease in MM. 7,8 The use of self-tanning products containing dihydroxyacetone (DHA) could potentially decrease UVR exposure in the population, 9,10 which might lead to a decrease in MM.…”