The classic LM/LMM dermoscopic specific structures include:

Shiffner et al showed that the presence of asymmetrically pigmented follicular openings, gray dots, gray globules, or rhomboidal structures located anywhere within a lesion has a sensitivity of 89 % and a specificity of 96 % for LMM [2]. Pralong et al found that at least one of these structures is present in 87 % of LMMs [13]. The presence of gray color appears to be a useful clue to the diagnosis of LMM [14]. In a series of 201 LMMs, gray color was present in 88.6 % of cases [15]. Tschandl et al further reported that any gray structures, such as dots, circles, or lines, were present in 95.8 % of LMM lesions with a relative risk of 8.9 (95 % CI: 1.2–64.7) [16]. While gray color is possible in pigmented actinic keratosis and LPLK, this color is rare in solar lentigo and flat seborrheic keratosis.

Less prevalent dermoscopic features associated with LM/LMM include the isobar structure or the “circle-within-a-circle”, identified in 5 % and 25.4 % of cases in 2 separate series [15, 16]. More recently described features include red rhomboidal structures, increased lesional vascular network density, and target-like pattern [13]. Red rhomboidal structures are created by a diamond or rhomboid-shaped vascular pattern occurring between hair follicles, and were reported to be present in 40 % of cases [13]. An increased density of the vascular network within the lesion compared to the peripheral skin was found in 58 % of cases [13]. A target-like pattern, defined as a dark dot in the center of the dark circle of a hyper-pigmented hair follicle, has been found in 19.4 % and 41 % of cases [13, 15]. Finally, the perception of the degree of pigment present within a lesion is a clue to the diagnosis of LM/LMM. In 25 % of LM/LMM the pigment appears darker and more variegated with different shades of brown and gray when viewed with dermoscopy compared to naked-eye examination [13].

It is plausible that certain LM/LMM-specific features are related to the type/thickness of the melanoma, the anatomical location of the tumor, or to patient-specific phenotypic factors. For example, Tiodorovic-Zivkovic et al showed that rhomboidal structures are more frequently seen in LMM located on the upper part of the face (p = 0.028), whereas asymmetric follicular openings were more common in LMM located on the lower part of the face (p = 0.036) [15]. Table 4.1 summarizes frequency and diagnostic accuracy of dermoscopic features of LMM.