Author Affiliations: Dermatology Research Centre, The University of Queensland, School of Medicine, Princess Alexandra Hospital, Brisbane, Australia.
Acquired melanocytic nevi are a well-known risk factor in the development of melanoma; their increased frequency is associated with increased risk. Many recent studies have focused on the dermoscopic diagnosis of melanoma in addition to investigation of nevogenesis.1,2 However, the clinical appearance of nevus orientation has not been a target of investigation. Although not aiming to identify new phenomena, we attempt herein to quantify and explain the orientation patterns of acquired melanocytic nevi on the back. Blaschko lines are a well-described pattern of skin lines that correlates with epidermal nevi and may relate to acquired melanocytic nevus orientation.3 Quatresooz et al,4 while investigating lines of tension in skin on the back, identified a dermoscopic parallel melanotic line pattern on the normal skin of the back aligned with skin tension lines called Langer lines.4 We propose that a pattern of acquired melanocytic nevus orientation is identifiable and may be associated with both Blaschko and Langer lines.
Our study protocol was approved by the University of Queensland ethics board (project No. 2009001590). To investigate the observed orientation of melanocytic nevi on the back, we assembled a cohort of 20 white participants (10 women) recruited from the Dermatology Outpatients Department at the Princess Alexandra Hospital, Brisbane, Australia. Each participant underwent full-body imaging (FotoFinder machine; FotoFinder Systems GmbH) and subsequent dermoscopic imaging of all nevi greater than 5 mm in diameter on their back. Each nevus was analyzed, and its long-axis length and total area were recorded. The nevi's longest axis was used to assess its angle of orientation with reference to the patient's midline. Measurement of each nevi's eccentricity (“ovalness”) was then calculated for correlation of nevus shape with other recorded parameters.
Each back image was cropped based on common surface landmarks to include the base of the neck to the natal cleft and scaled to a standard size of 1500 × 2500 pixels (Figure 1). The coordinates of each nevus were recorded in addition to the angle of orientation from the vertical axis of the spine (range, 0°-360°) measured as shown in Figure 2.
Figure 1. Cropped patient image used for recording nevus orientation between the base of the neck and the natal cleft. Dimensions are 1500 × 2500 pixels.
Figure 2. Measurement of nevus angle. A, Left of midline, the angle is measured from the vertical in an anticlockwise direction. B, Right of midline, the angle is measured from the vertical in a clockwise direction.
The median age of our cohort participants was 47 years. Our analysis included data from 440 individual nevi in total. Nevus orientation was investigated in relation to vertical and horizontal position of the back. Figure 3 demonstrates the recorded orientation corresponding to vertical displacement as a fraction of the distance from neck to natal cleft. Statistical analysis revealed a quadratic relationship between nevus orientation and vertical position, with a coefficient of determination of R2=0.61.
Figure 3. Individual nevus angle is shown to be dependent on vertical position on the back. Individual nevi are represented by the black dots. The curving trend line indicates a predictive model relating nevus angle to vertical position on the back following the quadratic equation y = −213.3 x2 + 162.3 x + 121.4.
No relationship was observed between horizontal position and nevus angle, but all recorded lesions had an angle between 80° and 180°. No relation was found between horizontal position and size or vertical position and size. Additionally, the angle of orientation did not show any association to any measurement of acquired melanocytic nevus size or shape.
Through full-body imaging, we observed a specific and reproducible pattern of acquired melanocytic nevus orientation and have confirmed this observation by identifying a mathematical model relating nevus orientation to vertical location on the back. Given the documented correlations between Blaschko lines, Langer lines, and previously described epidermal lesions and pigmentation patterns, we hypothesized that a relationship may exist between nevi orientation and either Blaschko lines or Langer lines.
Our investigation of the relationship between acquired melanocytic nevus orientation and Blaschko lines was not supported by our data. If this association did exist we would observe a V shape centered along the spine typically seen in conditions allowing visualization of Blaschko lines. This was not present in our analysis.
Conversely, our orientation data did reasonably match Langer line patterns. Compilation of our data into a composite patient allowed visual comparison of our recorded data and Langer lines. The correlation between our data and Langer lines on the back can be seen in an image overlay in Figure 4. We conclude that acquired melanocytic nevi on the back are aligned with Langer lines, and the correlation is independent of size and eccentricity.
Figure 4. Composite patient data plot and line association. A, All recorded lesions drawn at corresponding coordinates, size, and orientation. B, Langer lines of the back, adapted from Langer.5 C, Overlay of lesion data plot and Langer lines.
This quantification of nevus orientation has given strength to the hypothesis that acquired melanocytic nevi align with Langer lines. This may lead to a better understanding of the underlying factors involved in nevus growth.
Correspondence: Dr Soyer, Dermatology Research Centre, The University of Queensland, School of Medicine, Princess Alexandra Hospital, 199 Ipswich Rd, Woolloongabba, Brisbane, Queensland 4102, Australia (firstname.lastname@example.org).
Accepted for Publication: December 29, 2011.
Author Contributions: Drs McClenahan and Blake had full access to all of the data in the study and take full responsibility for the integrity of the data and accuracy of the data analysis. Study concept and design: McClenahan, Blake, Gilmore, and Soyer. Acquisition of data: McClenahan, Blake, and Douglas. Analysis and interpretation of data: McClenahan, Blake, and Gilmore. Drafting of the manuscript: McClenahan and Blake. Critical revision of the manuscript for important intellectual content: McClenahan, Blake, Douglas, Gilmore, and Soyer. Statistical analysis: McClenahan and Gilmore. Obtained funding: Soyer. Administrative, technical, and material support: Blake. Study supervision: Douglas and Soyer.
Financial Disclosure: None reported.
Funding/Support: This study was supported by research grant APP1004999 from the National Health and Medical Research Council (Dr Soyer).
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