Background B-cell depletion therapy (BCDT) may improve the efficacy of conventional idiopathic inflammatory myopathies (IIM) treatment. However, administration of such drugs is associated with increased risk of adverse events, first of all – infections.

Objectives To assess the risk of infections in IIM patients receiving rituximab (RTM).

Methods The study included IIM patients who required RTM therapy because of interstitial lung disease (ILD) or active myositis when administration of effective glucocorticoid (GC) dose was not possible. All patients continued treatment with GC and cytostatic drugs (CSD). RTM was administered at 1000 mg or 2000 mg doses (2 infusions of 500 mg or 1000 mg with 2 week interval). All patients were thoroughly examined at baseline and thereafter each 3 months after RTM infusion. Follow up period varied from 3 months to 4 years.

Results 38 IIM patients were enrolled (5 males and 33 females aged 22- 79 years, with 3-313 months duration of the disease). 22 patients received one RTM course, the rest 16 patients received 2 – 7 RTM courses. In the first course 17 patients received 2000 mg, 21 – 1000 mg of RTM, in each subsequent course 1000 mg were administered. At initiation of RTM all patients were on conventional therapy with GC in the dose varied from 10 to 90 mg/day prednisone equivalent (14 patients were taking 5 - 20 mg/day, 24 – more than 20 mg/day); 25 were taking CSD: 18– cyclophosphamide 600-2000 mg/month, 2– mycophenolate mofetil 1,5-2 g/day, 2- methotrexate 20 mg/week, 1- azathioprine 150 mg/day. Among patients taking GC at a dose ≤20 mg/day urinary tract infection was registered in 4 cases (3 – asymptomatic bacteriuria, 1- pyelonephritis), as well as one case of each - sinusitis and bronchitis. Among patients taking GC at a dose ≥20 mg/day there were 5 cases of pneumonia, 1 case of oropharyngeal candidiasis, 1- urogenic sepsis, 1- hepatitis B virus reactivation, 3 – herpes virus (HSV) infection, 1- immunosuppressive Kaposi sarcoma associated with HSV type 8 infection, and latent mycobacterial infection in 1 patient was diagnosed in 6 months after first RTM infusion. Infections usually occurred in 2-3 months after the first RTM infusion. All patients with upper and lower respiratory tract infections had ILD at baseline. There were 2 deaths in the cohort due to pneumonia and urogenic sepsis in patients with severe course of the disease. In remaining patients infection was eventually successfully controlled with no relapses (except for the only patient with bronchiectases and ILD, who had recurrent pneumonias). Tumor reduction was documented in Kaposi sarcoma patient.

Conclusions High activity of IIM in association with high or moderates GC doses and severe IDL at initiation of RTM therapy are the predictors of serious infectious adverse events. The highest risk emerges in 2-3 months after the first RTM infusion. Raising RTM dose up to 2000 mg was not associated with increased rate or severity of co-morbid infections. It remains unclear to what degree high doses of GC themselves would increase the risk of infectious complications.

Disclosure of Interest None declared