Background: Rituximab (anti-CD20) has been used as B-cell-targeted intervention to treat opsoclonus-myoclonus syndrome. Due to isolated reports of chronic hypogammaglobulinemia and B lymphopenia following rituximab in several disorders, and rapid B-cell depletion after a few doses, we reduced the dosage 20% in our clinical practice.
Methods: In this Institutional Review Board-approved retrospective study, 32 children with opsoclonus-myoclonus syndrome and cerebrospinal fluid B-cell expansion had received front-loaded adrenocorticotropic hormone, intravenous immunoglobulin, and rituximab combination immunotherapy for de novo opsoclonus-myoclonus syndrome. Parametric statistical analysis compared 10 children receiving 1200 mg/m2 of rituximab (300 mg/m2 × 4) and 22 receiving 1500 mg/m2 (375 mg/m2 × 4). Clinical response had been video documented and scored by a blinded observer.
Results: In both groups, motor severity (total score) lessened by ≥76% and cerebrospinal fluid B cells were similarly depleted (≥95%) six months after treatment. None of the treated patients remained unable to walk independently. Serum IgM depletion was analogous in the 1200 mg/m2 (-73%) and 1500 mg/m2 group (-64%). The relapse frequency was similar in both groups. Side effects were principally steroidal, tolerable, and transient. Circulating B-cell repopulation was comparable.
Conclusions: The reduced-dose of rituximab in rituximab combination immunotherapy was as effective and well tolerated as the standard dose, and provided rapid, early therapeutic intervention in opsoclonus-myoclonus syndrome. Pending a long-term prospective study, these are proof-of-concept data in support of challenging the dose of rituximab in various disorders, which may have different dose requirements.
Keywords: Anti-CD20; B-cell depletion; CSF B cells; neuroblastoma; neuroinflammation; opsoclonus-myoclonus syndrome; paraneoplastic syndrome; pediatric neuroinflammatory disorders.
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