Transverse myelitis (TM) is associated with neuromyelitis optica (NMO) and multiple sclerosis (MS). Early recognition of useful parameters may be helpful to distinguish their difference. This retrospective study analyzed thyroid parameters from 243 serum samples (relapse = 128; remission = 115) of 178 patients with demyelinating diseases (NMO, n = 25; TM, n = 48; MS, n = 105). The relationship between thyroid and clinical parameters was analyzed. Patients with NMO and TM had a higher frequency of abnormal thyroid-stimulating hormone (TSH), anti-thyroglobulin antibodies (TG-Ab), and antithyroid peroxidase antibody (TPO-Ab) than MS patients (p<0.05). The level of TSH and TG-Ab returned to normal levels after administration of high-dose intravenous methylprednisolone (p<0.05). In 96 patients (NMO, n = 19; TM, n = 25; MS, n = 52) without treatment, serum levels of TSH, TG-Ab and TPO-Ab were significantly different between patients with and without myelitis (p<0.01). Patients positive for aquaporin-4 (AQP4) antibodies showed higher abnormalities of TSH (p = 0.001), TG-Ab (p = 0.004) and TPO-Ab (p<0.0001) levels than AQP4 antibodies negative patients. Logistic regression analyses revealed independent relationships between TSH (odds ratio [OR] = 33.994; p<0.0001), TG-Ab (OR = 7.703; p = 0.017) and myelitis occurrence in 96 patients at the active stage. In 52 MS patients experiencing their first attack, MS patients with myelitis were associated with TSH abnormalities (OR = 42.778; p<0.0001). This study showed increased abnormalities of thyroid parameters in patients with NMO and TM than in MS patients. MS patients with myelitis also had greater TSH abnormality than in MS patients without myelitis. Abnormal TSH and TG-Ab were independently associated with myelitis occurrence in central nervous system demyelinating disorders.