Some patients may benefit from using finer needles for facial onabotulinumtoxinA injections, although the procedure is well tolerated by most. Results of a small randomized, double-blinded split-face study of 30- vs. 32-gauge needles found that the patient experience was improved for some when the smaller needle diameter was used.

Dr. Murad Alam of Northwestern University, Chicago, and his colleagues used a split-face design to assign 20 female patients to receive onabotulinumtoxinA with a 30-gauge needle on one side of the face and a 32-gauge needle on the left side. Injections were performed for moderate dynamic forehead and glabellar wrinkles (JAMA Dermatol. 2015 Sep 9. doi: 10.1001/jamadermatol.2015.2232 ).

Patients were randomized according to which needle bore was used first, and according to which size bore was used on which side of the face. The 20 patients also received injections of saline on the inner upper arm with needles of each diameter. This study design, together with masking the needle hub size to ensure operator blinding, “significantly mitigated inadvertent bias” that may have been present in previous needle size studies, according to Dr. Alam.

Primary outcome measures included patient-reported pain using an 10-point visual analog scale (VAS), as well as the proportion of patients whose pain was identified as being clinically significant (set by study parameters as more than 5.4 on the VAS scale). The secondary outcome measure of patient-reported pain characteristics was assessed by use of the Short-Form McGill Pain Questionnaire.

The injections were tolerated well by most patients, regardless of needle size, so statistical adjustments were made for the large proportion of patients who reported no pain with either needle bore. Overall, needle bore did not make a statistically significant difference in mean pain levels for either the face or arm injection sites.

However, the likelihood of clinically significant pain during facial injection (pain reported as over 5.4 on the VAS) was significantly higher with the larger needle. Eight of 20 (40%) patients reported clinically significant pain from the 30-gauge needles, compared with just three reports (15%) of clinically significant pain from the 32-gauge needles (odds ratio, 3.80; P = 0.04). The difference was not seen for arm injections, and the character of the pain did not differ between the two needle types.

Noting that 32-gauge needles are about 25% smaller in external diameter than 30-gauge needles, but that they are more expensive, Dr. Alam and his colleagues suggested that use of the finer needles could be “restricted to the subset of patients who have in earlier treatments encountered clinically significant pain with large-bore needles.”

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