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The Prevalence and Predictive Factors of Painful Tonic Spasm in Patients with Neuromyelitis Optica Spectrum Disorder (NMOSD)

Background: Painful tonic spasm (PTS) is a complication frequently observed in patients with neuromyelitis optica spectrum disorder (NMOSD).
Objective: To identify the prevalence of PTS, compare the factors associated with the occurrence of PTS, define the characteristics of PTS, and correlate the medication and prognostic factors with good recovery from PTS in patients with NMOSD.
Materials and Methods: A retrospective study was performed in patients with definite NMOSD in the Prasat Neurological Institute between January 1, 2014 and December 31, 2018. The prevalence and characteristics of PTS were explored. The characteristics and factors associated with the occurrence of PTS were investigated. Moreover, the factors associated with PTS recovery and pain medications were further analyzed in the present study. 
Results: The prevalence of PTS in patients with NMOSD was 37.81%. The factors associated with the occurrence of PTS were the presence of acute myelitis (p=0.002, OR 39.00, 95% CI 3.89 to 391.23), and tobacco use (p=0.048, OR 13.38, 95% CI 1.02 to 175.52). In the subgroup analyses of the factors associated with PTS recovery, plasma exchange (p=0.007, OR 24.70, 95% CI 2.43 to 251.57), and Expanded Disability Status Scale range 1.0 to 4.5 (p=0.008, OR 6.92, 95% CI 1.67 to 28.65) were related to the recovery from PTS. While non-recovery was correlated with older age at last visit (p=0.013, OR 1.09, 95% CI 1.02 to 1.17) and longer segments of cord lesions (p=0.016, OR 1.21, 95% CI 1.04 to 1.42).
Conclusion: The present study supports that PTS is one of the common complications in patients with NMOSD in Thailand. The presence of acute myelitis and the tobacco use are associated with the presence of PTS. Plasma exchange treatment in the acute phase of NMOSD may be associated with good recovery from PTS, and longer segments of spinal cord lesions is correlated with poor recovery outcomes. The control of these factors may prevent the occurrence of PTS or at least facilitate the recovery from PTS in these patients.
Keywords: Neuromyelitis optica spectrum disorder (NMOSD), Painful tonic spasm (PTS)