Background: Patients with large congenital melanocytic nevi (LCMN) are at risk for neurocutaneous melanocytosis (NCM). Patients with LCMN on the posterior axis or in conjunction with many satellite melanocytic nevi seem to represent subgroups at greatest risk.
Objective: To determine the relationship between LCMN location, number of satellite nevi, and risk of NCM.
Design: Descriptive survey study.
Setting: An Internet Web-based registry of patients with LCMN, maintained by a nevus support group (Nevus Outreach Inc).
Participants: Individuals with LCMN or their guardians visiting the Nevus Outreach Web site were provided the opportunity to complete the questionnaire.
Outcome measures: Location of LCMN, number of satellite nevi, and NCM as assessed by patient self-report.
Results: A total of 379 patients with LCMN were evaluated, 26 of whom had NCM. A significantly higher percentage of patients with NCM had their LCMN on the posterior axis compared with patients without NCM (96% and 70%, respectively). Patients with NCM had significantly more satellite melanocytic nevi compared with non-NCM patients (median, 68.5 and 18, respectively). Furthermore, patients with LCMN and more than 20 satellites had a 5.1-fold (95% confidence interval, 1.9-14.0) increased risk for NCM compared with LCMN patients with 20 or fewer satellites. Logistic regression analysis, controlling for age, sex, number of satellite nevi, and LCMN location, identified number of satellite nevi as the only significant risk factor for NCM.
Conclusions: The presence of large numbers of satellite nevi is the most important risk factor for NCM in patients with LCMN. Although location of the LCMN on the posterior axis was a moderate risk factor for NCM in univariate analysis, the strength of the relationship was attenuated in the multivariate analysis.