Reflectance Confocal Microscopy Findings in a Small-Diameter Invasive Melanoma
The diagnosis of a small-diameter melanoma may be challenging. We report the case of a 57-year-old man with a small pigmented papular lesion (2.5-mm diameter) that was suspicious on dermoscopy. A more confident differential diagnosis between an atypical nevus and a melanoma was necessary for correct management. Reflectance confocal microscopy (RCM) allowed a confident diagnosis in this lesion, which was an invasive melanoma with 0.3-mm Breslow thickness. This case highlights the benefit of RCM to reach a confident diagnosis and correct management of a small-diameter invasive melanoma.
Practice Points
- Melanomas with a long-axis diameter smaller than 6 mm are considered small melanomas, and those with diameters of 3 mm and smaller are considered micromelanomas; both are difficult to detect.
- Digital dermoscopic monitoring and reflectance confocal microscopy are important tools in detecting small melanomas.
The distinction of a small-diameter melanoma from a nevus via RCM relies on evaluation of the architectural and cellular features. Findings on RCM in small-diameter melanomas have been scarcely reported in the literature; Pupelli et al10 evaluated small melanomas with a diameter of 2 to 5 mm. Among these small-diameter melanomas, the RCM features suggestive for melanomas were the presence of cytologic atypia with cellular pleomorphism, architectural disorder with irregular nests, at least 5 pagetoid cells/mm2, dendrites or tangled lines (ie, short fine lines with no visible nucleus interlacing with the adjacent keratinocytes) within the epidermis, and atypical roundish cells at the DEJ.10
The distinction between an atypical nevus and a small-diameter melanoma using RCM occasionally may be challenging.11 Pellacani et al12 reported an algorithm to distinguish melanoma from atypical nevi. According to this algorithm, when at least 1 of the architectural atypia features (irregular junctional nests, short interconnections between junctional nests, and nonhomogeneous cellularity within junctional nests) and at least 1 of the cytologic atypia features (round pagetoid cells or atypical cells at the DEJ) are observed simultaneously, the lesion is diagnosed as a dysplastic nevus or a melanoma in the first step. In the second step, the RCM diagnosis of melanoma requires at least 1 of 3 parameters: roundish pagetoid cells encompassing at least 50% of the lesional area at the spinous layer, atypical cells involving at least 50% of the lesional area at the DEJ level, and nonedged papillae involving at least 10% of the lesional area.12 Accordingly, our case corresponded with these RCM criteria for a melanoma, given that there were irregular junctional nests, atypical cells at the DEJ, and nonedged papillae involving at least 10% of the lesion.
The current limitations of RCM are the high cost of the device (approximately $58,125–$139,400 for different models), the amount of time needed to train staff in RCM units (seminars, congresses, and special courses organized by the International Confocal Working Group), and the amount of time needed for evaluation of individual lesions (15–20 minutes). However, RCM can be valuable in the clinical diagnosis of difficult lesions, as seen in our case.
Conclusion
Our case highlights the benefit of RCM in allowing the confident diagnosis and correct management of a small-diameter melanoma that turned out to be a melanoma with 0.3-mm Breslow thickness. Even so, histopathologic evaluation remains the gold standard for the diagnosis of melanoma.
