Palmoplantar SH is a well-known mimicker of acral melanoma [1]. When a pigmented skin lesion is found on the palms or soles, most Asian patients, including Koreans, seem to be very anxious due to the possible risk of acral melanoma [7]. This is because the acral volar skin is the most common site of malignant melanoma in non-white populations [5]. Therefore, a few studies have attempted to delineate the characteristic dermoscopic findings of SH [1, 2]. Although these studies have revealed some characteristic dermoscopic findings of SH, more specific and systematic studies are needed to delineate the exact ratios and differences of the typical dermoscopic features of SH and acral nevi or melanoma-associated patterns.
Dermoscopy is a helpful, non-invasive tool that improves diagnostic accuracy in pigmented skin lesions [8–10]. Although SH is a common pigmented lesion on acral volar skin, studies on the dermoscopic features of SH are rare. Saida et al. were the first to describe the dermoscopic features of SH and coined the term “pebbles on the ridges,” denoting reddish-black droplets distributed on the ridges of skin markings [5]. Since then, only two related original studies have been reported [1, 2]. Zalaudek et al. described the dermoscopic features of 15 SH lesions [1]. They revealed that the most common color of SH was red-black (40%), followed by brown-black (13.3%), and gray-black (13.3%). In their study, the most common dermoscopic patterns were the homogenous pattern (8/15, 53.3%), followed by the globular pattern (7/15, 46.7%), the PRP (6/15, 40%), the parallel furrow (1/15, 6.7%) and the fibrillar pattern (1/15, 6.7%). Elmas et al. described the dermoscopic features of 20 SH lesions and reported that the most common color was red-black (45%), followed by brown (20%) and red (15%) [2]. They revealed that the most common dermoscopic pattern was the homogenous pattern (13/20, 65%), followed by the globular pattern (11/20, 55%), and the PRP (8/20, 40%). No patients showed parallel furrow or fibrillar patterns. However, these studies were performed on a small scale and provided insufficient results for the differentiation from acral melanoma [1, 2].
In this study, we coined the term bruise color sign after observing similar colors to bruises or contusions on nonvolar skin. Compared to typical bruise colors (pink and red, blue and dark purple, pale green, yellow and brown), SH showed black but no blue/green colors [4]. We speculated that the reason for this was the “Tyndall effect” considering that the depth of SH is much shallower than that of a usual bruises or contusions. Over four-fifths (43/50, 86.0.%) of patients in this study showed the bruise color sign, of which the red hue was the most common (35/43, 81.4%). In addition, the bruise color sign was positive in most cases with acral melanoma-associated dermoscopic patterns (32/36, 88.9%) (Table 4). This provides a useful tool for SH that shows acral melanoma-associated dermoscopic patterns. In this study, approximately three-fourths (37/50, 74.0%) of patients showed a red hue, which was also predominant (35/43, 81.4%) in the bruise color sign. A red hue is not common in acral melanoma except in irregular polymorphic or hairpin-like vessels, ulcers, or milky red areas; a red hue, especially as part of the bruise color sign, can also be useful for the differential diagnosis with acral melanoma [7, 11].
Table 4
The correlation between acral melanoma-associated patterns and bruise color sign
| | Acral melanoma-associated (n = 36) |
| | PRP (n = 26) | Irregular dots and globules (n = 25) | Polychromia (n = 17) | Asymmetry (n = 12) | Irregular blotches (n = 5) | Ulcer (n = 5) | |
Bruise color sign | + | 23 | 24 | 17 | 12 | 5 | 5 | |
- | 3 | 1 | 0 | 0 | 0 | 0 | |
PRP, parallel ridge pattern. |
Legends |
Different from previous studies, this study clearly divided the dermoscopic patterns of SH into three categories: hematoma-associated, acral nevus-associated, and acral melanoma-associated patterns. In this study, we adopted only two typical hematoma-associated patterns (red to black homogenous pattern with or without satellite globules and pebbles on the ridges). Three-fifths of cases (30/50, 60%) showed one of these hematoma-associated dermoscopic patterns. Satellite globules, red to black globules at the periphery, can be an important dermoscopic pattern for SH. We found this pattern in 15 cases (15/50, 30%), which consisted of pebbles on the ridges (n = 9), a red to black homogenous pattern (n = 4), and PRP without pebbles (n = 2). Compared to the study by Zalaudek et al. [2], this ratio was somewhat lower (hematoma-associated dermoscopic patterns: 60% vs. 80%, satellite globules: 30% vs. 46.7%).
Although approximately half of the cases had a globular pattern in other studies (Zalaudek et al. [1]: 46.7%, Elmas et al. [2]: 55%), and quite a few cases showed parallel furrow and fibrillar patterns (Zalaudek et al. [1]: 3.3%), we could not find any case with acral nevus-associated dermoscopic patterns. Although we found 25 cases with multiple dots and globules, they did not correspond to the globular pattern of acral nevomelanocytic nevus that is not typically associated with a parallel pattern. In these cases, the patterns were irregular dots and globules, such as in the melanoma pattern but not in acral nevus. Some of them (n = 14) were associated with PRP.
In this study, 36 cases (36/50, 72%) showed acral melanoma-associated dermoscopic patterns. Of these, PRP (26/50, 52%) was the most common, followed by irregular dots and globules (25/50, 50%), polychromia (17/50, 34%), asymmetry (12/50, 24%), irregular blotches (5/50, 10%), and ulcers (5/50, 10%). We could not find any case with blue-white veils, regression structures, atypical vascular pattern, or irregular fibrillar patterns.
Mun et al. described the dermoscopic features of acral melanoma in situ (n = 25) and reported that the most common dermoscopic pattern was an asymmetric pattern (88%), followed by the PRP (84%), irregular dots and globules (40%), irregular blotches (24%), regression and irregular fibrillar pattern (each, 8%), ulcer, blue-white veil, and atypical vascular patterns (each, 4%), and polychromia (0%) [7]. We believe that the present results and those of Mun et al. [7] could help differentiate ambiguous cases between acral melanoma and SH. In other words, we diagnosed SH if polychromia was noticed; vice versa, acral melanoma was presumed to be present when blue-white veils, regression structures, atypical vascular patterns, or irregular fibrillar patterns were found.
Among the various dermoscopic features of acral melanoma, PRP is the most prominent [12]. Thus, most dermoscopists tend to diagnose acral melanoma when observing PRP, although PRP can be found in SH, lentiginosis, racial melanosis, acral melanocytic nevi, drug-induced hyperpigmentation, and dye-related pigmentation [13]. Therefore, we need to know how PRP differs between SH and acral melanoma. More than half of the PRP cases in this study showed pebbles on the ridges, which is the most characteristic hematoma-associated dermoscopic pattern. In the 12 cases without pebbles on the ridges, the color of PRP was red (n = 3), black (n = 3), or brown (n = 6). Considering that the color of PRP is black or brown in acral melanoma, nine cases in this study showed a PRP similar to that of acral melanoma. However, four cases of brown PRP showed a brick wall-like structure, which has not been reported for acral melanoma. The remaining five cases with black or brown PRP (5/26, 19.2%) were similar to acral melanoma-associated PRP. Taking these results into account, the PRP of SH is quite different from that of acral melanoma, as SH-associated PRP presents with pebbles on the ridges, a red hue, and a brick wall-like structure.
As we considered the bruise color sign to be a potentially meaningful dermoscopic feature of SH, we analyzed the dermoscopic patterns in the seven cases without the bruise color sign. They were composed of a brown to black homogenous pattern (n = 3), brown PRP with a brick wall-like structure (n = 2), red PRP (n = 1), and red irregular dots and globules (n = 1), which were not relevant to the dermoscopic findings of acral melanoma.
The limitations of our study could be its retrospective design and small sample size, although this was the largest sample reported so far in the literature.
In conclusion, we found and proposed some meaningful results for the features of SH and the dermoscopic differences between SH and acral melanoma. The exact ratio of the typical dermoscopic features of SH, acral nevus, and acral melanoma-associated patterns were 60%, 0%, and 72%, respectively. Although more than half of SH (26/50, 52%) cases could have PRP, the PRP seen in SH had pebbles on the ridges, a red hue, and a brick wall-like structure, which were not reported in PRP seen in acral melanoma. As new findings, we coined a new term, the bruise color sign, which could be a characteristic feature of SH and useful for discriminating SH from acral melanoma. Furthermore, we propose that a presumptive diagnosis of SH can be made if polychromia is noticed; vice versa, acral melanoma can be diagnosed when blue-white veils, regression structures, atypical vascular pattern, or irregular fibrillar patterns are found.
We believe that the results of this study are very useful for dermatologists encountering ambiguous cases between SH and acral melanoma.