nevus spilus ( ns ) is a potential precursor of melanoma ; the vast majority of cases reported in the literature were histologically classified as superficial spreading melanoma . to demonstrate the diagnostic value of reflectance confocal microscopy ( rcm ) in this subtype of congenital nevi . we report a case of a large congenital ns with equivocal clinical and dermoscopic findings in which rcm was applied for diagnosis and follow - up . there was a good correlation of rcm with histopathology and a lack of dynamic changes during follow - up . our observations indicate that rcm , as a non - invasive tool , can be useful for diagnosis and follow - up of clinically and dermoscopically equivocal ns . nevus spilus ( ns ) is a relatively common cutaneous lesion that is seen in 23% of the population . it is characterized by numerous small , darkly pigmented macules or papules on a tan background pigmentation and is also referred to as  speckled lentiginous nevus , the background tan patch is usually present at birth and ns is therefore considered a subtype of congenital melanocytic nevus . the typical dimension of ns ranges from 2 to 10 cm , but some ns may cover extensive skin areas with regional or zosteriform distribution . histologically , the background hyperpigmentation has been described as having the features of a lentigo simplex or a caf - au - lait macule . the darker speckles of ns are classically reported as superimposed junctional or compound nevi , but intradermal , spitz , and blue nevi may occasionally occur . ns are potential precursors of melanoma , which underlines the need for a precise examination and a close lifelong follow - up to exclude malignancy . the risk that melanoma develops within a ns is thought to be proportional to the size of the lesion and has been reported to be higher for macular than for papular ns . more than 20 cases of melanoma arising within a ns have been reported in the literature ; over 90% of these cases were histologically classified as superficial spreading melanoma . with the following case report , we will show for the first time that in vivo reflectance confocal microscopy ( rcm ) , as a convenient non - invasive method for skin investigation , is useful in diagnosis and follow - up of ns . a 15-year - old girl was referred to our outpatient department because of a giant congenital ns covering her right scapular region and upper aspect of her right arm . recently , the patient had noticed the development of multiple darkly pigmented spots within the nevus . skin examination revealed multiple light to dark brown macules and papules within the ns , measuring 0.2 to 3 cm in diameter ( figure 1 ) . dermoscopy of the newly developed lesions showed a brown to black homogeneous or homogenous - reticular pigment pattern with focal gray - blue areas , suggestive of regression ( figures 2a and 3a , c ) . in addition , many of the lesions displayed irregularity of the pigment network and irregular dots , altogether raising the suspicion of malignancy . in vivo rcm ( vivascope 1500 , mavig gmbh , munich , germany ) of a representative lesion showed a typical honeycomb pattern at epidermal layers and a regular ringed pattern at the dermoepidermal junction ; uniformly distributed dermal papillae surrounded by a rim of bright monomorphous cells , correlating to pigmented keratinocytes and melanocytes , were seen ( figure 2b , c ) . additionally , small junctional aggregates of melanocytes protruding into the dermal papillae were found . at upper dermis , there were focal aggregates of non - nucleated plump bright cells compatible with melanophages . these results correlated well with the histopathologic findings , which were consistent with the diagnosis of  junctional melanocytic nevus without atypia  ( figure 2d ) . the remaining newly developed lesions within the ns showed similar confocal findings suggestive of benign nevi . these lesions were monitored with digital dermoscopy and rcm and did not show any changes at a three - month follow - up visit ( figure 3 ) . the progressive appearance of macules and papules within a ns , as observed in our case , is not unusual . although the majority of these newly arrived lesions are benign , a risk for melanoma exists ; therefore , a close follow - up of large ns is essential since their dimensions rarely permit a complete surgical excision . rcm , as a new method capable of producing real - time in vivo sections of the skin at a nearly histologic resolution , permits cytological analysis to complement dermoscopy and histopathology for melanoma detection . multiple studies have already demonstrated excellent correlation between confocal microscopy and conventional histology for melanocytic lesions . despite its maximum in vivo imaging depth of approximately 250 m therefore , rcm should be adequate for the detection of melanoma within ns , since most cases reported were superficial spreading melanomas . in addition , this technique allows completely safe and painless repetitive application and observation of dynamic changes in situ over time and consequently may reduce unnecessary excisions . the good correlation of rcm with histopathology in our case indicates that rcm , as a non - invasive tool , can be used as an auxiliary for differentiation of nevi from melanoma in clinically and dermoscopically equivocal ns .
background : nevus spilus ( ns ) is a potential precursor of melanoma ; the vast majority of cases reported in the literature were histologically classified as superficial spreading melanoma.objective:to demonstrate the diagnostic value of reflectance confocal microscopy ( rcm ) in this subtype of congenital nevi.methods:we report a case of a large congenital ns with equivocal clinical and dermoscopic findings in which rcm was applied for diagnosis and follow-up.results:there was a good correlation of rcm with histopathology and a lack of dynamic changes during follow-up.conclusion:our observations indicate that rcm , as a non - invasive tool , can be useful for diagnosis and follow - up of clinically and dermoscopically equivocal ns .