Low T3 syndrome in neuromyelitis optica spectrum disorder: Associations with disease activity and disability

Background Neuromyelitis optica (NMO) sometimes coexists with serological marker-positive, non-organ-specific autoimmune disorders. We evaluated the prevalence of thyroid dysfunction and anti-thyroid antibodies in patients with NMO spectrum disorder (NMOSD) and investigated the associations between thyroid dysfunction/autoimmunity and clinical features of NMOSD. Methods Forty-nine NMOSD patients with anti-aquaporin-4 antibody and 392 age- and sex-matched healthy controls were included. We measured the levels of thyroid hormones and anti-thyroid antibodies. Results The prevalence of clinical hypothyroidism, subclinical hyperthyroidism, and low T3 syndrome were higher in patients with NMOSD (4.1%, 12.2%, and 20.4%, respectively) compared with healthy controls (0.3%, 2.8%, and 0.5%, respectively; p = 0.034, p = 0.001, and p < 0.001, respectively). However, anti-thyroperoxidase antibody (anti-TPO)-positivity did not significantly differ between NMOSD patients (20.4%) and controls (11.5%). Low T3 syndrome was more prevalent among patients during an attack (N = 10/19, 52.6%) than those in remission (N = 1/30, 3.3%). In addition, patients with low T 3 syndrome had significantly higher EDSS scores at the last visits as well as at sampling compared to those without low T3 syndrome. T3 levels were inversely correlated with EDSS score at the last visit after adjustment for age, sex, disease duration, clinical status (attack vs. remission), oral prednisolone use, iv methylprednisolone use, other immunosuppressive agents use, and the location of lesion (ρ = −0.416, p = 0.010). Conclusions Our study suggests that thyroid dysfunction is frequent in patients with NMOSD; particularly, serum T3 levels may be a useful indicator of disease activity and disability in NMOSD.