Rituximab’s potential as PMR treatment ‘encouraging’

Researchers have reported promising findings from the first study to assess the effect of the B-cell depleting agent rituximab in patients with polymyalgia rheumatica.

As B cells have been implicated in the pathogenesis of polymyalgia rheumatica, Dutch clinicians sought to determine whether the potential use of rituximab could reduce the current reliance on glucocorticoids for treatment, given the challenges linked with their use, including the high number of patients with contraindications or experiencing adverse events.

The 21-week exploratory study, led by Dr Diane Marsman from the Department of Rheumatology, Sint Maartenskliniek, in the Netherlands and published in the Lancet Rheumatology, included 47 patients, either with newly diagnosed polymyalgia rheumatica (38) or with relapsing disease on 7·5 mg per day or more of prednisolone (9).

Patients were randomly assigned to either receive intravenous rituximab (1 x 1000mg infusion) or placebo in addition to 50mg methylprednisolone, followed by a 17-week prednisolone taper to 0mg.

The primary outcome of glucocorticoid-free remission at week 21 was reached in nearly half of patients (48%) in the rituximab group compared to 21% in the placebo arm, the researchers said.

Rituximab also showed a significant benefit versus the control within some of the study’s secondary outcomes, including the proportion of patients taking glucocorticoid dose of 5mg per day or less (100% versus 54%, respectively) and a mean change in clinical activity score of -13.8 versus -3·8, respectively.

However, there were no significant improvements seen for other secondary endpoints, such as cumulative glucocorticoid dose and relapses post follow-up.

The results are “encouraging” as they show “modest signals of clinical efficacy for rituximab”, and suggest that B cells “might have an important role in the immune pathology of polymyalgia rheumatica”, noted researchers at the University of Groningen’s Department of Rheumatology and Clinical Immunology, in a comment led by Dr Maria Sandovici and published in the Lancet Rheumatology.

However, they also urged caution in interpreting the results due to the study’s small sample size and short duration, and said a longer-term, phase 3, randomised controlled trial is needed to further substantiate the results of the present study and to inform on the long-term efficacy and safety of rituximab in patients with polymyalgia rheumatica.

“If these findings are confirmed by larger trials, rituximab could be a valuable glucocorticoid-sparing treatment for patients with polymyalgia rheumatica,” the study authors concluded.

Meanwhile, a group of French researchers have suggested that abatacept may be considered as a potential adjunctive therapy in selected or difficult cases of PMR, based on its effects in Giant Cell Arteritis (GCA).

They reported success in treating two of four patients with PMR who had steroid-refractory disease and had undergone unsuccessful treatment with methotrexate and the IL-6 inhibitor tocilizumab. Two patients responded to the treatment with a progressive decline in PMR activity score and tapering of steroid dosage over a 12-month follow-up period, they reported in the Journal of Rheumatology.

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