Juvenile dermatomyositis is the most common type of juvenile idiopathic inflammatory myopathy mainly affecting the skin and proximal muscles. We have published the Japanese version of 'Clinical practice guidance for juvenile dermatomyositis (JDM) 2018 'consisting of a review of articles in the field and evidence-informed consensus-based experts' opinion on the treatment strategy in collaboration with The Pediatric Rheumatology Association of Japan and The Japan College of Rheumatology under the financial support by 'Research on rare and intractable diseases, Health and Labor Sciences Research Grants'. This article is a digest version of the Japanese guidance.

Background Vaccination to prevent hepatitis B (HB) virus infection is important for children undergoing immunosuppressive treatment. Information on the efficacy of HB vaccination in children with rheumatic diseases undergoing immunosuppressive therapy is scarce. Methods Children with rheumatic diseases administered HB vaccine during immunosuppressive treatment between May 2013 and September 2016 were enrolled. Patients were vaccinated three times (primary series). Those who remained seronegative after the primary series received a secondary series of vaccinations. Patient baseline characteristics and treatment details from the medical records were retrospectively investigated. The proportion of patients that was seropositive for HB virus antibody after primary‐and secondary series of vaccinations was calculated. Associations between immunosuppressants and serostatus were evaluated. Results Fifteen of 26 patients (58%) produced anti‐hepatitis B surface antibody (anti‐HBs) after the primary vaccinations. Eight of 10 patients (80%) taking methotrexate and 3 of 11 (27%) taking mycophenolate mofetil (MMF) were seropositive. Multivariate analysis adjusted for dosage of prednisolone per body weight. Multivariate analysis showed MMF was a factor impeding seroconversion (odds ratio 0.093, 95% confidence interval 0.014–0.615). In six of seven patients (86%) who received a secondary series of vaccinations, anti‐HBs were produced. Conclusions MMF may impede seroconversion after a primary series of HB vaccinations, thus requiring secondary series of vaccinations in pediatric patients with a rheumatic disease undergoing immunosuppressive therapy.

O. N. Atkas declares no relevant conflicts of interest.

Similar to findings in Western countries, the clinical characteristics of JDM in Japanese may differ for each type of MSAs.

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