Rheumatoid meningitis sine arthritis: An emerging cause of isolated pachymeningitis and leptomeningitis with typical features

Rheumatoid meningitis (RM) is a meningeal inflammation rarely occurring during the course of rheumatoid arthritis (RA). Anti-citrullinated protein antibodies (ACPA), which are highly specific biomarkers of RA, may allow RM sine arthritis (RMSA) to be diagnosed as an extra-articular early lesion of RA. MRI typically displays pachymeningitis and/or leptomeningitis predating convexity, and CSF diffusivity is focally restricted. Blood ACPA is a strong clue and intrathecal synthesis of ACPA is characteristic although rarely reported. We report two cases of RMSA that were confirmed by meningeal biopsy and intrathecal synthesis. RMSA abated after steroids alone or associated with rituximab. No arthritis occurred during the follow-up. RM can occur in the absence of RA.