CONVEY is a multicenter, double-blind, enriched enrollment randomized withdrawal study conducted in 6 phases: screening assessment (≤21 days), taper (≤14 days), washout (5 days), open-label (OL) run-in (4 weeks), double-blind (DB, 12 weeks), follow-up (~4 weeks). Key inclusion criteria: ≥18 years old with ≥6-month and ≤10-year history of probable SFN, Average Daily Pain (ADP) Score (11-point Numerical Rating Scale, 0 [no pain]-10 [worst pain]) ≥5 and ≤9 during 7 days before screening and confirmed abnormality in a single skin biopsy. Participants have pain medications tapered (if needed), followed by washout before beginning OL vixotrigine 350 mg twice daily (BID). At the end of the OL run-in, responders (≥30% improvement in mean ADP score over previous 7 days versus baseline, defined as the 5 days prior to the first dose of study treatment in the OL period) continuing to meet enrollment criteria are eligible for randomization (1:1:1; vixotrigine 200 mg: vixotrigine 350 mg: placebo, all BID). Throughout the study, patients track pain symptoms daily in an electronic diary; weekly mean  ADP scores are calculated. Acetaminophen use is permitted during the OL and DB periods, within pre-specified limits. The primary endpoint is the change from baseline to DB Week 12 in the mean ADP score. Safety assessments include adverse events and serious adverse events.