Unusual Cerebral Involvement of Rheumatoid Arthiritis Mimicking a Tumor

BACKGROUND: The central nervous system's involvement in Rheumatoid Arthritis (RA) is infrequent and can be life-threatening. Mass-like CNS involvement is an unusual presentation. A 45 year old man had suffered seropositive rheumatoid arthritis for five years referred to our hospital with one-week history of right-sided facial paralysis, left hemiparesis and headache. DISCUSSION: MRI demonstrated hyperintense mass-like lesion extended from mesencephalon to right hippocampus and basal ganglia on T2 and FLAIR images. On DWI, restricted diffusion was not present. After contrast administration, minimal contrast enhancement was noted. After methotrexate and steroid treatment, the size had been markedly shrunken on the follow-up images. The clinical symptoms were also improved. CONCLUSION: To our knowledge, the mass-like presentation was not reported in the literature. We report an unusual case of brain involvement of rheumatoid arthritis mimicked tumor.