Oral cyclophosphamide in treatment of patients with refractory idiopathic inflammatory myopathies: a retrospective observational study.

To describe the use of oral cyclophosphamide (PO CYC) in a single center longitudinal cohort of patients with idiopathic inflammatory myopathies (IIM). Patients using PO CYC were identified through a retrospective chart review of a myositis cohort at a single academic center. PO CYC dose, duration, adverse events, and disease activity measures before and after CYC were analyzed. Disease activity measures included muscle enzymes, manual muscle testing (MMT8), 100-mm visual analog scale (VAS), and 1-4 Likert scale for physician global assessment. Fourteen patients were treated with PO CYC within the cohort between 2008 and 2017; 9 dermatomyositis (DM), 3 polymyositis (PM), and 2 with immune-mediated necrotizing myopathy (IMNM). Age was 51.1 (40-72) years and the cumulative dose of PO CYC was 41 (2-131) grams over duration of 12.4 (0.5-43) months, mean (range) for all. All patients had severe refractory IIM, 10 (72%) with ILD, 3 (21%) with cardiac involvement and 4 (29%) were dependent in most activities of daily living. Median number of prior failed therapies was 4.5 (range 3-6) including intravenous CYC in 5 patients. Disease activity measures significantly improved following CYC use and concomitant daily prednisone dose decreased. The most common adverse events during CYC therapy were infections. We report the first cohort study of PO CYC use in IIM patients with severe, treatment refractory disease. Further trials are needed to verify these results as well as to evaluate long-term safety outcomes.