Effect of needle size on pain perception in patients treated with botulinum toxin type a injections: A randomized clinical trial

IMPORTANCE: Transcutaneous injection through smaller hollow-bore needlesmay decrease patient discomfort, but current evidence is equivocal. OBJECTIVE: To compare injection discomfort in patients treated with botulinum toxin type A with 30- and 32-gauge needles. DESIGN, SETTING, AND PARTICIPANTS: Split-face, patient- and injector-blinded randomized clinical trial at the dermatology service of an urban university medical center. The 20 participants were women aged 25 to 70 years in good health and with moderate dynamic forehead and glabellar wrinkles. Data were collected from November 20, 2013, through January 16, 2014. Follow-up was complete on January 16, 2014. Data from the per-protocol population were analyzed from July 1 to July 31, 2014. INTERVENTIONS: One side of each patient's forehead received botulinum toxin type A in saline injected with a 32-gauge needle; the other side received the same treatment injected with a 30-gauge needle. In addition, each patient received randomized injections of saline only to both upper inner arms with the same types of needles. MAIN OUTCOMES AND MEASURES: Primary outcomes included the patient-reported pain rating on a visual analog scale (VAS) on either side of the face and arms and the proportion of patients whose VAS ratings corresponded with more than moderate (ie, clinically significant) pain. The secondary outcome consisted of patient-reported information about the character of the pain at both sites using the expanded and revised version of the Short-Form McGill Pain Questionnaire. RESULTS: All 20 patients completed the study. Overall, facial and arm injections were nominally but not significantly more painful with 30-gauge needles (mean [SD] VAS ratings for the face, 4.16 [2.55] vs 3.41 [2.31], P = .34; for the arm, 1.66 [2.07] vs 1.21 [1.65], P = .45). For facial injections, the likelihood of clinically significant pain (VAS rating,≥5.4) was significantly greater with 30-gauge needles, which were associated with such pain in 8 patients (40%) compared with the 32-gauge needles, which were associated with such pain in 3 patients (15%) (odds ratio, 3.80 [95%CI, 1.05-13.78]; P = .04). No difference was found in the character of pain associated with needle bore (P > .05 for all comparisons). CONCLUSIONS AND RELEVANCE: For facial injections of neurotoxin in saline, 30-gauge needles were associated with greater incidence of clinically significant pain than 32-gauge needles. For patients prone to experience clinically significant pain with facial injections, use of 32-gauge needlesmay minimize this discomfort.