Autoimmune markers were negative for antinuclear anti- bodies (ANA), anti-SSA and anti-SSB antibodies, anti- TPO antibodies, anti-thyroglobulin antibodies, anti-phos- holipid antibodies and anti-DS DNA antibodies, but posi- tive for low level of anti-NMDAR Ab (performed by Oxford University Hospital Laboratory, UK; normal range: no antibodies detected). Further testing demonstrated pos- itive beta 2 adrenergic and M2 muscarinic receptor anti- bodies (Berlin Cures, Germany). A paraneoplastic panel, including ganglionic AchR antibody, was negative. Serum anti-NMDA Ab were repeated 2 months later and were once again mildly elevated. To rule out a paraneoplastic syndrome with positive anti-NMDA Ab, a pelvic ultra- sound was obtained and did not reveal any ovarian or pelvic masses. Subsequently, a full body FDG-PET scan was performed and was also unremarkable. CSF analysis was negative for anti-NMDA Ab and other neuronal anti- bodies and showed normal cell count, glucose and protein. The patient received 5 treatments with plasmapheresis followed by a daily dose of prednisone, and her symptoms improved significantly for about 7 weeks after the treat- ment. When plasmapheresis was stopped and prednisone was tapered, the symptoms recurred. Following plasma- pheresis and prednisone treatment, a repeat serum anti- NMDAR Ab were negative.