Bidirectional association between vitiligo and melasma: A large-scale population-based study.

Background The dual diagnosis of vitiligo and melasma and their association has hardly been studied. Objective To test our hypothesis of an independent bidirectional association between vitiligo and melasma. Methods A population-based study was conducted on 24,436 patients with vitiligo and 119,205 matched comparators. Both a retrospective cohort design and a nested case-control design were used, with the calculation of adjusted hazard ratios (HRs) and odds ratios (ORs). Results The incidence of melasma per 1000 person-years was 1.38 (95% CI 1.22-1.54) in the vitiligo group and 0.88 (95% CI 0.84-0.96) in the comparison group. Patients with vitiligo had a 60% increased risk of developing melasma regardless of hormonal treatment, phototherapy, and thyroid disorders (adjusted HR, 1.58; 95% CI, 1.35-1.86). The prevalence of pre-existing melasma was higher in patients with vitiligo than in matched comparators (0.9% vs. 0.5%, P<0.001). Melasma was associated with a 30% increase in the odds of developing vitiligo (adjusted OR 1.32; 95% CI 1.12-1.55), regardless of hydroquinone treatment. Limitations Retrospective data collection. Conclusion A bidirectional association between vitiligo and melasma was observed. Treatment strategies for individuals with a dual diagnosis warrant further investigation.