Hashimoto's encephalopathy (HE) and anti N-methyl-D-aspartate receptor (NMDAR) encephalitis have clinical overlaps.

A 70-year-old woman presented with acutely developed confusion, disorientations and psychosis. HE was suspected based on goiter, markedly elevated anti-thyroglobulin and anti-thyroid peroxidase antibody. She was placed on high dose steroid and intravenous immunoglobulins administration, which did not ameliorate her symptoms. After the antibodies to the NMDAR were identified, weekly 500 mg of rituximab with 4 cycles were started. The current followed up indicated a complete recovery.

The possible associations between NMDAR antibody and autoimmune thyroid antibodies in anti-NMDAR encephalitis with positive thyroid autoantibodies remain unclear. However, a trend toward a higher incidence of NMDAR antibody in patients with autoimmune thyroid antibodies than without has been observed. Cases of encephalitis with only NMDAR antibody (pure anti-NMDAR encephalitis) also occur. Therefore, it is important for clinicians to know the clinical and pathogenic differences between anti-NMDAR encephalitis with positive thyroid autoantibody and pure anti-NMDAR encephalitis for relevant treatment, predicting prognosis, and future follow-up.