Objectives: Longitudinally extensive transverse myelitis (LETM) with spinal cord lesions spanning three or more vertebral segments is a key feature of neuromyelitis optica (NMO). However, the role of anti-aquaporin 4 (anti-AQP4) antibody, a sensitive biomarker of NMO, in the conversion of LETM to NMO remains uncertain.
Methods: Thirty first-ever LETM patients were retrospectively analysed and divided into two groups according to the presence of anti-AQP4 antibodies.
Results: Eighteen (60%) patients presented with anti-AQP4 antibodies. Fifteen (83.33%) anti-AQP4 (+) LETM patients converted to NMO, while only three of 12 (25%, p = 0.002) anti-AQP4 (-) LETM patients progressed to NMO, over a mean follow-up period of 5.63 years. Seven (38.89%) anti-AQP4 (+) and one (8.33%) anti-AQP4 (-) LETM patients received interferon-β1a treatment, respectively. Anti-AQP4 (+) LETM patients demonstrated a higher immunogamma globulin (IgG) index (0.68 ± 0.43 versus 0.47 ± 0.19, p = 0.018), annual relapse rate (0.72 ± 0.31 versus 0.42 ± 0.17, p = 0.01) and Kurtzke Expanded Disability Status Scale (4.28 ± 2.22 versus 2.67 ± 2.26, p = 0.031), than anti-AQP4 (-) LETM patients. In spinal magnetic resonance imaging (MRIs), more than half (58.33%) of the anti-AQP4 (+) LETM patients were observed to have central grey matter-predominant involvement in the axial view, while peripheral white matter-predominant involvement (51.85%) was the most common pattern observed in the anti-AQP4 (-) LETM patients.
Conclusion: Anti-AQP4 (+) LETM demonstrated a high conversion rate to NMO (83.33%), suggesting that anti-AQP4 (+) LETM may represent an early, isolated syndrome of NMO spectrum disorder. The greater number of patients receiving interferon-β treatment in anti-AQP4 (+) LETM may contribute to its high annual relapse rate.