Melanocytic naevi clustered on normal background skin

Area of Science:

• Dermatology
• Genetics
• Pathology

Background:

• Maculopapular melanocytic nevi can present in multiple forms with nonrandom skin arrangements.
• Segmental grouping is a common pattern observed in various types of nevi.

Purpose of the Study:

• To classify and define different patterns of segmentally arranged melanocytic nevi.
• To differentiate nevi associated with neurofibromatosis type 1 (NF1) from non-NF1 associated lesions.
• To propose terminology for mosaic presentations of various nevi types.

Main Methods:

• Observational analysis of clinical presentations of multiple melanocytic nevi.
• Classification based on lesion morphology, arrangement (segmental, checkerboard, agminated), and association with NF1.
• Review of existing literature and case studies on nevi patterns.

Main Results:

• Two types of segmentally arranged lentigines identified: NF1-associated (scattered, light-brown) and non-NF1 associated ('checkerboard-arranged lentigines', densely packed, dark).
• Blue nevi, Spitz nevi, and common acquired melanocytic nevi can form agminated clusters or checkerboard patterns.
• Segmental dysplastic melanocytic nevi are proposed as mosaic forms of dysplastic nevus syndrome, with subtypes 'isolated segmental' and 'superimposed segmental'.

Conclusions:

• Melanocytic nevi exhibit diverse nonrandom segmental and patterned arrangements, suggesting underlying mosaicism.
• Specific terminology is proposed for distinct clinical presentations, aiding in diagnosis and understanding of mosaic conditions.
• Small congenital melanocytic nevi and linear lentiginous nevi follow Blaschko lines, distinct from other patterned nevi.