Rituximab leading to an atypical presentation of neuroborreliosis and false negative serology.

Two patients, recently treated with the B-cell-depleting monoclonal antibody, rituximab, had 2-3 months of progressive systemic symptoms; comprehensive investigations did not clarify the diagnosis. Transient radicular pain at disease onset had suggested neuroborreliosis, but seronegativity and an atypical clinical course made this unlikely. However, PCR identified Borrelia burgdorferi DNA in cerebrospinal fluid, establishing the diagnosis of neuroborreliosis. Both the clinical picture and the laboratory findings can be atypical in people with neuroborreliosis who have recently been treated with rituximab. In B-cell depleted patients living in endemic areas, one should suspect neuroborreliosis even when the typical symptoms are drowned out by more atypical symptoms; PCR should be used as a diagnostic supplement when the serological response is uncertain or absent.