A score that predicts aquaporin-4-IgG positivity in patients with longitudinally extensive transverse myelitis

Background: Longitudinally extensive transverse myelitis (LETM) associated with aquaporin-4 autoantibodies (AQP4-IgG) can cause severe disability. Early diagnosis and prompt treatment are critical to prevent relapses. We describe a novel score based on clinical and neuroimaging characteristics that predicts AQP4-IgG positivity in patients with LETM. Methods: Patients were enrolled both retrospectively and prospectively from multiple Italian centers. Clinical and neuroimaging characteristics of AQP4-IgG positive and negative patients were compared through univariate and multivariate analysis. Results: Sixty-six patients were included. Twenty-seven (41%) were AQP4-IgG positive and median age at onset was 45.5 years old (range 19-81, interquartile range 24). Female sex (odds ratio [OR] 17.9; 95% confidence interval [CI] 2.6-381.9; p=0.014), tonic spasms (OR 45.6; CI 3.1-2197; p=0.017) and lesion hypointensity on T1-weighted images (OR 52.9; CI 6.8-1375; p=0.002) were independently associated with AQP4-IgG positivity. The Aquaporin-4-IgG positivity in Myelitis (AIM) score predicted AQP4-IgG positivity with 85% sensitivity and 95% specificity. Positive and negative likelihood ratio were 16.6 and 0.2 respectively. The inter-rater and intra-rater agreement in the score application were both excellent. Conclusions: The AIM score predicts AQP4-IgG positivity with good sensitivity and specificity in patients with a first episode of LETM. The score may assist clinicians in early diagnosis and treatment of AQP4-IgG positive LETM.