A Phase 2 Placebo-Controlled, Double-Blind, Enriched Enrollment Randomized Withdrawal Study to Evaluate the Efficacy and Safety of BIIB074 (Vixotrigine) in Treating Pain Experienced by Subjects With Confirmed Small Fiber Neuropathy That is Idiopathic or Associated With Diabetes Mellitus

The primary objective of this study is to evaluate the efficacy of BIIB074 in treating pain experienced by participants with confirmed small fiber neuropathy (SFN) that is idiopathic or associated with diabetes mellitus. A secondary endpoint that relates to the primary objective is the change from Randomization to Week 12 of the double-blind period in mean average daily pain score.The secondary objectives of this study are to evaluate the effect on worst pain, neuropathic pain quality, sleep interference due to pain, patient global impression, use of rescue medication, and SFN symptoms in participants treated with BIIB074; to investigate the safety and tolerability of BIIB074 in participants with SFN; and to characterize the pharmacokinetics (PK) of BIIB074 in participants with SFN.