Clinical Efficacy of Cysteamine Application for Melasma: A Meta-Analysis

Background: Melasma is a challenging, acquired hyperpigmentary disorder. The gold standard treatment is Kligman's formulation, which contains hydroquinone, tretinoin, and dexamethasone, but its long-term use is limited by the risk of exogenous ochronosis. Cysteamine, a tyrosinase inhibitor, reduces melanocyte activity and melanin production, showing strong depigmenting effects in patients resistant to Kligman's formulation. Nonetheless, clinical studies have yielded inconsistent efficacy results. This meta-analysis aimed to assess the efficacy of cysteamine in treating melasma and to identify potential factors that may impact its therapeutic outcomes. Methods: A systematic search of PubMed, Embase, Web of Science, and CENTRAL, from the earliest record until August 2024, was conducted. Randomized controlled trials and quasi-randomized design studies related to topical cysteamine on melasma patients were included. The primary outcome was MASI or mMASI assessment after treatments. The current meta-analysis was conducted with a random-effects model. Subgroup analyses and meta-regressions were performed based on baseline MASI, disease duration of melasma, patient age, and sample size of the included studies. Funnel plots and Duval and Tweedie's trim and fill method were adopted to assess the publication bias. Results: Eight studies were included for quantitative analysis. The analysis of MASI after topical cysteamine demonstrated a significant decrease compared to the placebo (p = 0.002). Compared to other melasma treatments, cysteamine did not show superior efficacy in mMASI (p = 0.277). The treatment efficacy of hydroquinone, modified Kligman's formula, and tranexamic acid mesotherapy for melasma was not statistically different when compared to cysteamine (p = 0.434). Further analyses showed no benefit when allowing extended cysteamine application time (p < 0.0001). The meta-regression revealed the efficacy of cysteamine decreased as the duration of melasma increased (coefficient = 0.38, p = 0.0001, R² = 0.99). The funnel plot displayed some asymmetry. The trim and fill method suggested the adjusted effect size was 0.607 (95% CI = -0.720 to 1.935). Conclusions: Cysteamine exhibited efficacy in treating melasma patients; however, its depigmentation effect was comparable to hydroquinone-based regimens, tranexamic acid mesotherapy, and modified Kligman's formula. Using cysteamine in patients with a short duration of melasma may result in better efficacy.