Symmetric Plantar Melanocytic Nevi - Site-Specific Phenomenon or Pure Chance

Background: Predilection sites of melanocytic nevi are highly variable; however, individual patterns (e.g. preponderant involvement of extremities, trunk, etc.) are often noticed. A symmetric appearance of nevi on both sides of the body has not been reported. Objective: Guided by an initial, incidental observation of symmetrically arranged plantar nevi, a prospective survey of palmoplantar nevi was carried out. Methods: Between January 2016, and January 2017, 886 patients underwent a full-body examination for skin cancer screening. Special attention was paid to the pigmentary characteristics of the palms and soles. Results: 12/886 patients exhibited symmetrically or nearly symmetrically distributed plantar nevi (1.35%; mean age 45 years; male-female ratio 1:1). The nevi were mostly situated on the medial part of the plantar arch (9/12 cases; 75%). Remarkably, not a single case of symmetric nevi was identified on the palms. Conclusion: Arguments in favour of the specifity of the finding are: 1) the lack of comparable findings in palmar skin, i.e., in a similar histological compartment and 2) the predominant localization in the foot arch. Symmetric plantar nevi appear to be a rare, but not a random event. Possible underlying causes of this phenomenon are discussed.