To explore the clinical significance of low T3 syndrome in patients with antibody-negative autoimmune encephalitis (AE) and assess clinical characteristics of patients reclassified with alternative diagnoses during follow-up.
Approach:
Study Design: Retrospective cohort study of patients diagnosed with antibody-negative AE from January 2016 to June 2024, comparing demographics, clinical features, and outcomes based on low T3 syndrome presence.
Key Findings:
23.68% of patients presented with low T3 syndrome during the acute phase (p = 0.048).
Patients with low T3 syndrome had a higher incidence of consciousness disturbances (p = 0.048) and more frequent motor impairments.
61.84% of patients achieved a favorable prognosis, while 38.16% had an unfavorable outcome.
Low T3 syndrome was associated with poor prognosis in univariable analysis but not after multivariable adjustment.
Discharge mRS was an independent predictor of unfavorable outcome (OR 0.293, 95% CI 0.103-0.834, p = 0.021).
Interpretation:
Acute-phase low T3 syndrome is common in antibody-negative AE but reflects disease severity rather than serving as an independent prognostic biomarker; discharge mRS is a more reliable predictor.
Limitations:
Small sample size of 76 patients ultimately analyzed.
Retrospective design may introduce bias.
Need for larger prospective studies to clarify the prognostic role of thyroid hormone alterations.
Conclusion:
A subset of patients (9.5%) initially diagnosed with antibody-negative AE received alternative diagnoses after 12 months, indicating diagnostic uncertainty and the need for clinical red flags for re-evaluation.
