Original 3-step algorithm1 for the management of acquired acral melanocytic lesions. The numbers indicate numbers of lesions (nonmelanoma or follow-up + melanoma). PFP indicates parallel furrow pattern; LLP, latticelike pattern.
Revised 3-step algorithm. The order of the second and the third steps in the original algorithm is reversed, and a new category without need of further follow-up is introduced. The numbers indicate numbers of lesions (nonmelanoma or follow-up + melanoma). PFP indicates parallel furrow pattern; LLP, latticelike pattern.
Dermoscopic image of an acral melanocytic lesion not conforming to any of the typical parallel furrow, latticelike, or regular fibrillar patterns. In this irregular fibrillar pattern, the starting or ending points of fibrils are not arranged on the lines corresponding to the furrows of the skin markings. In addition, overall pigment distribution is irregular and asymmetric. The size of this brownish macule was 9.5 × 7.4 mm, and biopsy specimens were taken and analyzed. Histopathologically, it was diagnosed as melanoma in situ.
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Koga H, Saida T. Revised 3-Step Dermoscopic Algorithm for the Management of Acral Melanocytic Lesions. Arch Dermatol. 2011;147(6):741–743. doi:10.1001/archdermatol.2011.136
Acral volar skin is the most prevalent site of malignant melanoma in nonwhite populations. In 2007, our group proposed a 3-step algorithm for the management of acquired melanocytic lesions affecting acral volar skin (Figure 1).1 We now know that almost all acral melanomas arise de novo, not in association with a preexisting acral nevus.2 Given that an acral nevus has virtually no risk of developing to acral melanoma, follow-up of a definitely diagnosed acral nevus is not necessary. Taking this point into account, we have revised the 3-step algorithm. In the revised algorithm, the order of the second and the third steps in the previous algorithm is reversed, and a new category without need of further follow-up is introduced.
We retrospectively applied the original and the revised algorithms to consecutive case series of acquired melanocytic lesions on acral volar skin first seen from January 2005 through December 2008. Congenital pigmented lesions, drug-induced pigmentation, volar melanotic macules, Peutz-Jeghers syndrome, and hemorrhage were excluded. Biopsied lesions were histopathologically evaluated by expert dermatopathologists.
The revised 3-step dermoscopic algorithm (Figure 2) proceeds as follows: in the first step, if a lesion shows the parallel ridge pattern (PRP), we biopsy it regardless of the size. If the lesion does not show the PRP, we proceed to the second step in which we check whether it shows any of the typical dermoscopic patterns of benign acral nevus on the whole area of the lesion (typical parallel furrow pattern, typical latticelike pattern, or regular fibrillar pattern). If the lesion shows these typical benign patterns, there is no need of further follow-up. However, if the lesion does not show any of these typical dermoscopic patterns, we proceed to step 3, in which we measure the maximum diameter. If the lesion is more than 7 mm in maximum diameter, we recommend biopsy for histopathologic evaluation (Figure 3). If the lesion is smaller than 7 mm in diameter, we recommend periodic clinical and dermoscopic follow-up.
A total of 191 acquired acral melanocytic lesions collected from 176 Japanese patients were enrolled. Numbers of lesions classified into each category of the original and revised algorithms are shown in Figures 1 and 2. A total of 17 lesions exhibited the PRP, and all 17 of these lesions were histopathologically diagnosed as acral melanoma.
In both algorithms, the same 26 lesions were categorized into the group not showing typical benign dermoscopic patterns and larger than 7 mm in diameter. Biopsy was performed in 19 of the 26 lesions, and the remaining 7 lesions were not biopsied because of refusal by patients or physically or psychologically complicated conditions of the patients. Of the biopsied 19 lesions, 8 lesions were histopathologically diagnosed as acral melanoma, In the original algorithm, 148 lesions were categorized into the group to be followed up. In contrast, in the revised algorithm, 101 lesions of the 148 lesions (68.2%) were categorized into the group without need of further follow-up, and the remaining 47 lesions (31.8%) were categorized into the group to be followed up periodically. In actuality, biopsy was performed in 28 of the 148 lesions categorized into the follow-up group in the original algorithm, and all of them were melanocytic nevi. The remaining 120 lesions were followed up for a median of 48 months (approximate follow-up range, 21-68 months). No significant changes in dermoscopic features were observed in any of these 120 lesions during the follow-up period.
In the original 3-step algorithm for the management of acquired acral melanocytic lesions, criteria for biopsy were clearly established, but all the other lesions were categorized into the group to be followed up. The relationship between acquired melanocytic nevi and malignant melanoma is still controversial. However, if limited only to acral melanoma, morphologic and molecular findings support de novo development without preexisting nevus.3,4 Dermoscopically, the typical pattern of early acral melanoma is the PRP, whereas that of acral nevus is the parallel furrow pattern or its variants.5 Although some temporal changes in dermoscopic features are detected in acral nevi, transition from the benign dermoscopic patterns to the PRP has been never observed.6,7 These findings support the de novo origin of acral melanoma. Thus, in our opinion, periodic follow-up is not necessary for definitively diagnosed acquired acral melanocytic nevus because it carries no risk of development to melanoma.
By using the revised algorithm, physicians can substantially reduce the number of lesions that need follow-up without missing early acral melanoma. We advise most patients in the follow-up category to visit us once or twice a year, though there is no evidence to specify adequate frequency of follow-up. Furthermore, we ask them to come back soon if the lesion enlarges to more than 7 mm.
In this revised 3-step algorithm, the most confusing point may be evaluation in the second step. Accurate identification of the typical dermoscopic patterns is essential in this step. To avoid missing early acral melanomas, if a lesion does not show stereotypical benign patterns, it should be classified into the category not conforming to the typical benign patterns.
Another possible problem in using this algorithm is differentiation between acquired and congenital acral nevi because the algorithm is designed only for acquired melanocytic lesions. Our group has recently reported dermoscopic patterns characteristic of congenital acral melanocytic nevi,8 which will help identify and exclude congenital acral nevi. However, it may be impossible for us to identify all the congenital acral nevi as such. Therefore, some congenital acral nevi are possibly evaluated with this revised 3-step algorithm. We believe that this does not cause a serious problem because the number of congenital acral nevi, particularly those classified into the category to be biopsied, may be very small.
In conclusion, we believe that the revised 3-step algorithm greatly aids clinicians in efficiently managing acquired melanocytic lesions on acral volar skin.
Correspondence: Dr Koga, Clinical Trial Research Center, Shinshu University Hospital, 3-1-1 Asahi, Matsumoto 390-8621, Japan (firstname.lastname@example.org).
Author Contributions: Both authors had full access to all of the data in the study and take responsibility for the integrity of the data and the accuracy of the data analysis. Study concept and design: Koga and Saida. Acquisition of data: Koga. Analysis and interpretation of data: Koga and Saida. Drafting of the manuscript: Koga and Saida. Critical revision of the manuscript for important intellectual content: Koga and Saida. Study supervision: Saida.
Financial Disclosure: None reported.