Efficacy of an adjuvant Lactobacillus rhamnosus formula in improving skin lesions as assessed by PASI in patients with plaque psoriasis from a university-affiliated, tertiary-referral hospital in São Paulo (Brazil): a parallel, double-blind, randomized clinical trial

Psoriasis is an inflammatory disease of the skin, characterized by erythematous plaques. It is rather common, affecting 2–4% of the population in western countries. Psoriasis’ etiology encompasses both genetic and environmental factors. Evidence suggests that the latter reflect the importance of changes in the microbiome for developing the disease. Thus, it is hypothesized that gut microbiome manipulation may arise as a way of treating psoriasis. However, few trials assessed the use of probiotics in psoriasis, although promising results were detected in small studies. Our objective was to assess the efficacy of adjuvant probiotics ( Lactobacillus rhamnosus ) in treating plaque psoriasis patients. This was a randomized, parallel, placebo-controlled, double-blind trial with two arms: experimental ( n = 50) and control ( n = 53). Inclusion of subjects and data gathering lasted from November 2020 to August 2021. Subjects were consecutive plaque psoriasis patients under regular follow-up in the Dermatology unit of a university-affiliated, tertiary-referral hospital in São Paulo (Brazil). Eligibility criteria included being over 18 years old, having plaque psoriasis and not having other skin diseases, neoplasms nor systemic inflammatory diseases. Subjects received standard-of-care plus probiotics ( Lactobacillus rhamnosus formula). Controls received standard-of-care plus placebo. Primary outcome was skin lesion improvement as assessed by psoriasis area of severity index (PASI) at six months. Secondary outcome was quality-of-life as assessed by dermatology life quality index (DLQI) at six months. Regarding within-group analyses, changes in both PASI and DLQI were non-significant for the experimental group (mean PASI decreased by 1.58, p = 0.105, and mean DLQI increased by 0.05, p = 0.873) and significant for controls (mean PASI decreased by 1.90, p = 0.019, and mean DLQI decreased by 3.33, p = 0.031). Between-group analyses returned non-significant results ( p = 0.620). Our findings do not support the hypothesis that gut microbiome modulation via ingestion of Lactobacillus rhamnosus produces clinical improvement in psoriasis patients. Further research is encouraged. Trial registration: Retrospectively registered at the Brazilian Clinical Trials Registry (RBR-8js7t83) on 08/02/2022.