C. C. Mok1, L. Y. Ho1, C. H. To1
1Medicine, Tuen Mun Hospital, Hong Kong, Hong Kong Special Administrative Region of China

Objectives: To report the efficacy and toxicity of rituximab in the treatment of refractory polymyositis.
Methods: Adult patients who met the Bohan and Peter criteria for definite or probable diagnosis of polymyositis were recruited under the following criteria; (1) Investigations did not reveal other underlying autoimmune diseases or malignancies; (2) Active myositis as evidenced by persistent proximal muscle weakness, elevated creatinine kinase (CK) and features of active myositis on electromyography for at least 4 months; (3) Refractory to corticosteroids and at least 2 other immunosuppressive agents. While immunosuppressive agents were continued, rituximab (375mg/m2) was given by intravenous infusion weekly for four consecutive weeks. Patients were followed up at baseline and then 4-weekly till the 28th week with serial assessment of muscle power (proximal and axial muscles) (0-10), serum muscle enzymes (CK, LDH, SGOT), physicians’ and patients’ global impression on disease activity (0-10), disability scores (HAQ) and quality of life.
Results: Four patients (3 women and 1 man) were studied. The mean age was 53 ± 11 years and the mean duration of polymyositis was 4.8 ± 3.3 years. All had persistently active myositis for at least 2 years. Muscle biopsy in these patients did not reveal any inclusion bodies. Previous ineffective therapies included high dose corticosteroids (N=4), intravenous pulse methylprednisolone (N=2), AZA (N=4), MTX (N=1), MMF (N=3), CSA (N=3), tacrolimus (N=1), intravenous immunoglobulin (N=3). At week 28, a significant improvement in the mean proximal muscle power scores (5.3 ± 3.8 to 7.3 ± 3.8; p=0.002) and reduction in CK levels (2632 ± 1583 to 661 ± 359 U/L; p=0.05) was observed in comparison to baseline. Two patients had return of full muscle power with significant drop in CK level. Moreover, there was a trend of improvement in disability scores and both the mental and physical components of the SF36 scores from baseline to week 20. Rituximab was well tolerated.

Conclusion: Rituximab is an option to be considered in refractory polymyositis and further controlled trials are necessary to confirm its efficacy.