Dual therapy with Erenumab and onabotulinumtoxinA: No synergistic effect in chronic migraine: A retrospective cohort study

Objective: To assess whether dual therapy with erenumab and onabotulinumtoxinA (BoNTA) was more effective than erenumab alone in chronic migraine.Background: Calcitonin gene-related peptide (CGRP) is crucial in migraine. Erenumab binds to the canonical CGRP receptor in A delta- fibers, and BoNTA prevents the release of CGRP from meningeal and extracranial C-fibers. It is still unknown whether dual therapy is more effective.Methods: This was a retrospective study in a Headache Unit. There was a thorough revision of charts of patients receiving erenumab from December 2019 to March 2021. The cohort was divided into three groups according to BoNTA at the start of erenumab: (1) WBT: were on BoNTA and maintained it as dual therapy; (2) WoBT: were on BoNTA and discontinued; (3) NoBT: were not on BoNTA. Primary endpoint was reduction in monthly headache days (MHD) at 12 weeks. Secondary endpoints were percent improvement and >_50% reduction in MHD.Results: Of 237 charts reviewed, 187 met the inclusion criteria. Seventy- three (39%) were included in WBT, 44 (23.5%) in WoBT, and 70 (37.4%) in NoBT. The reduction in MHD was less with dual therapy [WBT 4.7 +/- 7.68, WoBT 5.12 +/- 7.98 (p = 0.80), NoBT 8.21 +/- 7.84 p = 0.009]. The percentage of improvement was higher in the erenumab- alone group [NoBT 35%, WoBT 22.3% (p = 0.92), WBT 21.7% (p = 0.001)]. The probability of achieving a >_ 50% reduction in MHD was lower in WBT than in WoBT (OR 0.66, p = 0.35) and in the NoBT group (OR 0.57, p = 0.14).Conclusions: Our findings suggest that dual therapy is less effective than erenumab alone. However, since the design has multiple limitations, further prospective studies are required to validate these data.