Treatment of Pityriasis Rubra Pilaris with Daily Low-Dose Methotrexate: A Retrospective Cohort Study

Background: Pityriasis rubra pilaris (PRP) is a rare disease that is difficult to manage. Treatment options include corticosteroids, immunomodulatory drugs, and biologics. Available literature has primarily described the use of weekly dosing of methotrexate, but there is limited data investigating the effectiveness of daily low-dose methotrexate in PRP treatment. Methods: A retrospective cohort study was conducted from September 2010 to December 2019 to determine the effectiveness of daily low-dose methotrexate in treating PRP. Results: The average duration of follow-up was 13.5 months. 14 patients were treated with oral daily low-dose methotrexate. 13 patients (92.9%) showed improvement on oral daily low-dose methotrexate. Mean time to clinical response was 5.9 weeks. In seven patients (50%), complete response on methotrexate monotherapy occurred within an average of 11.9 months. 12 patients (85.7%) developed asymptomatic transaminitis that resolved in most patients (66.7%) after dose reduction. Conclusions: In this study, daily low-dose methotrexate was an effective treatment of PRP and may be considered in patients unresponsive to weekly dosing. Due to the high incidence of transaminitis, the authors recommend frequent lab monitoring and screening for risk factors. Further studies are warranted to elucidate the efficacy of daily low-dose methotrexate in the management of PRP.