Central Pain Study for ABX-1431

This is a double-blind, placebo-controlled crossover study, randomized, crossover study of ABX-1431 HCl as add-on therapy in the treatment of central neuropathic pain.The efficacy of ABX-1431 will also be assessed by the change in pain intensity scores using a numerical rating scale (NRS-11). All patients will undergo a screening visit for enrollment criteria. Eligible patients will be treated with daily medication for 7 to 9 weeks, which will include some treatment with placebo and some treatment with ABX-1431 HCl. Patients will use a web based application to record their daily average pain using a numerical rating scale (NRS-11). This study will enroll up to 32 patients with chronic central pain due to one of the four following diagnostic groups: Neuromyeliltis Optica Spectrum Disorder (NMOSD), longitudinally extensive transverse myelitis (LETM), Multiple Sclerosis (MS), and Transverse Myelitis (TM).