Clinical outcome following B cell depletion therapy in eight patients with refractory idiopathic inflammatory myopathy

To assess the efficacy of B lymphocyte depletion therapy (BCDT) in patients with refractive idiopathic inflammatory myopathy (IIM).

Eight patients thought to have IIM were treated with BCDT utilising rituximab. Five were treated as part of an open label trial and three on the basis of perceived clinical need. Rituximab (1 gram) and methylprednisolone (100 mg) were given as intravenous infusions on days 0 and 14. The primary efficacy outcome at 6 months was 15% improvement in muscle strength and 30% reduction in CPK.

Two patients with Jo-1 antibody positive dermatomyositis (DM) demonstrated a clinical response. Both achieved >30% improvement in CPK. In one, the CPK remained within the normal range for 10 months, the other had a normalised CPK and stabilisation of lung function tests for 36 months. Muscle strength by myometry, however, did not achieve the primary outcome, although, patient 1, demonstrated an improvement of 20% at 8 months (the patient had elective surgery of the hand during the study period). Jo-1 antibody levels fell modestly in both patients but remained detectable. Re-evaluation of three patients revealed that one had inclusion body myositis, one had sporadic muscular dystrophy and one subsequently developed nodular sclerosing lymphoma. All except one patient showed adequate B cell depletion with re-population occurring 3- >42 months after BCDT. One patient did not deplete and died of an unrelated cause.

This study emphasizes the importance of identifying and selecting the appropriate sub-group of patients with IIM most likely to respond to BCDT.