Objective: Previous studies have shown that functional abnormalities of the thyroid are associated with the pathogenesis of several neurological diseases. However, their relationship in patients with anti-N-methyl-D-aspartate receptor (anti-NMDAR) encephalitis remains to be defined. Methods: Forty-three patients with anti-NMDAR encephalitis were examined for thyroid function and autoimmune indications, in comparison with 225 healthy controls (CTL). Patients were further classified into 2 subgroups based on their free tri-iodothyronine (fT3) levels. Moreover, fT3 levels were also investigated after at least three months of follow-up. The clinical characteristics of the patients and CTL were described in detail. Results: Serum levels of fT3 and thyroid-stimulating hormone (TSH) were found to be relatively lower in patients with anti-NMDAR encephalitis than in CTL (both p < 0.001). Low T3 syndrome also occurred more frequently in anti- NMDAR encephalitis (25.6 vs. 0.4%, p < 0.001). However, no statistical differences were detected between patients and CTL in terms of the positive rate of thyroid antibodies and other types of thyroid dysfunction. Patients with low T3 levels tended to have a longer hospital stay (p = 0.006), a higher rate of abnormal brain magnetic resonance imaging (MRI) findings (p = 0.033), a higher frequency of consciousness declination (p = 0.029), and a higher modified Rankin scale (mRS) score during hospitalization. Low fT3 levels were also associated with abnormal MRI findings, a decline in consciousness, and the mRS score on admission. In addition, fT3 seemed to gradually return to normal levels upon improvement of the mRS score (r = –0.649, p = 0.002). Conclusions: Low T3 syndrome often copresents in anti-NMDAR encephalitis and indicates a longer hospitalization, abnormal MRI findings, consciousness declination, and a higher clinical severity. However, fT3 levels do not seem to influence the prognosis of anti-NMDAR encephalitis.

Keywords:
Anti-N-methyl-D-aspartate receptor encephalitis, Autoimmune diseases, Thyroid function, Thyroid antibodies, Low T3 syndrome
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