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Paper text:
acral ( lentiginous ) melanoma ( alm ) is the most prevalent subtype in the asian and mexican mestizo populations .
acral lentiginous melanoma is most often diagnosed at an advanced stage and associated with a poor outcome [ 24 ] .
dermoscopy is a noninvasive diagnostic technique that allows early recognition and increases diagnostic accuracy of pigmented skin lesions on acral volar skin [ 18 ] .
congenital melanocytic nevi ( cmn ) are defined as melanocytic nevi that are present at birth or become apparent shortly after .
acral cmn tend to show a greater size and a greater variability in color and shape than acquired nevi .
therefore , a histopathologic examination is sometimes required for differentiating acral cmn from alm , especially when the lesion has a large diameter and/or is clinical and dermoscopically atypical . according to previous studies , acral cmn show characteristic dermoscopic features such as a combination of the crista dotted and parallel furrow patterns
dermoscopically , the parallel ridge pattern is most commonly associated with alm in situ showing a high sensitivity ( 86% ) and specificity ( 99% ) for its diagnosis .
we , herein , present a case of acral cmn nevus with a parallel ridge dermoscopic pattern along with its histopathological correlates .
a 37-year - old , male patient , skin phototype iv , while being hospitalized for the treatment of schizophrenia , was seen for a 12 mm , pigmented skin lesion on his plantar arch ( figures 1 and 2 ) .
according to the patient s mother , the lesion had appeared shortly after birth and had been progressively enlarging in the course of the last years . under polarized dermoscopy ,
the melanocytic lesion was polychromatic with a central blue - grey area and dark and light brown colors in the periphery ; a central parallel ridge pattern blended with a peripheral lattice - like pattern associated with few asymmetric dots and globules .
based on the large size and the atypical dermoscopic presentation , the lesion was excised .
histologic examination revealed a very bland compound melanocytic neoplasm with clear - cut congenital - like features ( figure 4a ) .
the central area of the lesion was mainly an intradermal combination of type c and dendritic ( blue nevus - like ) melanocytes ( figure 4b ) , with a striking acrosyringial and periductal distribution ( figure 4c ) ; the junctional component was mainly peripheral , with regularly arranged nests without cytologic atypia ( figure d ) and melanin columns under the surface furrows .
this last histologic finding was also seen in the crista profunda intermedia ( figures 4d and 4e ) under the surface ridge in accordance with the dermoscopic appearance of the lesion .
dermoscopy is a powerful , noninvasive , diagnostic tool , which helps the clinical differential diagnosis between benign and malignant melanocytic lesions on volar skin .
it is commonly diagnosed at an advanced stage and associated with a poor outcome [ 24 ] .
however , it has also been described to occur in acral cmn as a relatively rare finding . in the latter occurrence , anamnestic data and stable clinicodermoscopic features on digital follow - up support the diagnosis of benignity . in our case ,
the lesion was reported as  congenital ,  but seemed to have been enlarging even in recent times .
this was interpreted as an atypical feature , inasmuch as cmn on acral volar skin commonly tend to fade over years   or , at least , do not commonly reveal a parallel ridge pattern .
dermoscopically , the pattern was atypical also because it was characterized by pigmentation along the ridges . furthermore
histopathologically , a dermal dendritic cell component was found as responsible for the central bluish area ; the striking growth of melanocytes surrounding the ductal compartment of the eccrine sweat glands might be considered as a further histopathological correlate for the central pigmentation along the ridges ( where acrosyringia emerge ) .
it has been recently proposed by some authors that eccrine melanocytic precursor cells may be the source of acral melanomas .
the junctional component was mainly peripheral and responsible for the lattice - like pattern , a quite common finding in melanocytic nevi of the plantar arch .
recently , chuah et al .   confirmed that acral congenital melanocytic nevi tend to be larger and more asymmetrical than acral aquired melanocytic nevi .
furthermore , they tend to be polychromatic and approximately 50% have a blue - grey coloration in the central portion of the lesion , which may be associated with the intradermal component .
other authors have also recorded a parallel ridge pattern in other benign conditions such as lentiginosis , racial melanosis , melanocytic nevi , drug - induced hyperpigmentation , subcorneal hemorrhage and dye - related pigmentation , particularly in darker skin phototypes .
our case is an example of acral cmn with a parallel ridge pattern observed in an adult .
acral cmn may be larger and more asymmetrical and polychromatic than acral acquired melanocytic nevi , but tend to fade or to become architecturally organized in adulthood .
thus , if the patient is uncertain whether the lesion has recently changed / enlarged and/or if follow - up can not be completed , histopathological examination may be required . in the final dermoscopic - pathologic evaluation of the case , one must remember that the dermoscopic features of an acral melanocytic lesion are best evaluated at its periphery .
acral melanoma is the most frequent subtype in the asian and mexican mestizo populations . 
 dermoscopy is a noninvasive diagnostic technique that helps the differential diagnosis of pigmented skin lesions on acral volar skin.we , herein , present a case of acral congenital melanocytic nevus with a parallel ridge dermoscopic pattern . since the parallel ridge pattern in a melanocytic lesion of the acral skin is classically ascribed to melanoma , the present case can be definitely labeled as  atypical  and worth of being elucidated in its histopathological correlates .