Resistance to cosmetic botulinum toxin A: A 15-patient case series across 12 sites

Resistance to cosmetic botulinum toxin A: A 15-patient case series across 12 sitesTo the Editor: With the increased popularity of cosmetic botulinum neurotoxin type A (BNTA) injections, evidence is emerging on the development of resistance in some patients. 1Although the exact prevalence or incidence of this phenomenon is likely modest overall, this study aimed to investigate clinical characteristics of complete BNTA resistance and to compare the effects of alternative neurotoxins attempts after diagnosis.The authors compiled a dataset stripped of identifiers (Supplementary Dataset, available via Mendeley at https://data.mendeley.com/datasets/m9wcp88h2j/ 2).Our series included 15 patients with a median onset age of resistance of 46 years (range: 31-76 years) and a median latency for developing resistance of 3 years (range: 0-14 years).Most patients were female (66.6%) and lived in urban areas (86.6%).The most commonly used initial BNTA was OnabotulinumtoxinA (73.3%).The median age at first injection was 40 years (range: 30-76 years).Before resistance, 8 (53.3%) received touch-ups.After resistance developed, the median follow-up duration was 5 years (range: 0.5-20 years).One-third of patients were on their usual dose at the last effective treatment and 26.7% were on escalating dose because of reduction of effect/duration (Table I).After resistance diagnosis, alternative BNTA treatments were attempted.Among those patients only exposed to alternative BNTA, 2 patients (13.3%) overcame resistance.Out of 7 patients transitioned to botulinum neurotoxin type B (RimabotulinumtoxinB), 85.7% responded; this was significantly higher than the response rate to another BNTA, P .0023 (Fisher's exact test).Among RimabotulinumtoxinB responders, resistance was observed in 2 cases, 1 after receiving 3 treatments of 5000 U, and 1 after the second dose of 2500 U, which resolved after a 1-year washout.Five (83.3%) are still receiving RimabotulinumtoxinB with good effect.Overall, the median response duration was 5 weeks (IQR: 1.5-5) and median dose was 5000 U (range: 2500e10,000 U).A dose of 10,000 U had 7week duration (Table II).This extremely rare resistance to cosmetic BNTA (only 15 cases identified our 12 sites), has been