Adding Chinese herbal medicine bath therapy to conventional therapies for psoriasis vulgaris: a systematic review with meta-analysis of randomised controlled trials

Background Chinese herbal medicine (CHM) bath is commonly used in China as an adjuvant therapy for managing psoriasis vulgaris. Previous systematic reviews showed that CHM bath therapy was effective and safe for psoriasis vulgaris, however, without exploration of the specifics of CHM bath therapy such as the optimal temperature, duration of each session, and the total treatment duration. Purpose To evaluate the add-on effects of CHM bath therapy to conventional therapies for adult psoriasis vulgaris. Methods We conducted a comprehensive search in nine medical databases from inception to September 2022 to identify relevant randomised controlled trials (RCTs) published in Chinese or English. The included studies compared the combination of CHM bath therapy and conventional therapies to conventional therapies alone for adult psoriasis vulgaris. Methodological quality assessment of the included RCTs was performed using the Cochrane risk-of-bias tool 2 (RoB 2). Statistical analysis was carried out using RevMan 5.4, R 4.2.3 and Stata 12.0 software. The certainty of evidence of outcome measures was evaluated using the Grading of Recommendations Assessment, Development, and Evaluation Working Group (GRADE) system. Results A total of 23 RCTs involving 2,183 participants were included in this systematic review. Findings suggested that the combination of CHM bath therapy and conventional therapies was more effective in reducing Psoriasis Area and Severity Index (PASI), Dermatology Life Quality Index (DLQI) and itch visual analogue scale, compared to using conventional therapies alone. These enhanced effects were notably observed when the CHM bath was set above 38°C and had a duration of 20 and 30 minutes, as assessed by DLQI. Moreover, an 8-week treatment duration resulted in better effects for PASI compared to shorter durations. Additionally, the top ten frequently used herbs in the included studies were identified. Despite the findings, the certainty of evidence was rated as ‘low’ or ‘moderate’ based on the GRADE assessment, and significant heterogeneity was detected in subgroup and sensitivity analyses. Conclusion The CHM bath therapy combined with conventional therapies is more effective and safer than conventional therapies alone for adult psoriasis vulgaris. The results suggest a potential correlation between treatment effects and factors such as extended treatment duration, increased bath temperature, and longer bath sessions. However, the certainty of evidence was downgraded due to methodological limitations of the included studies. To confirm the findings of this systematic review, a double-blinded, placebo-controlled RCT is needed in the future.