Reply: The Impact of Upper Face Botulinum Toxin Injections on Eyebrow Height and Forehead Lines: A Randomized Controlled Trial and an Algorithmic Approach to Forehead Injection

Sir: We thank Zhai and Qi for their comment on our article.1 They pointed out several issues that need further clarification. They stated “that the authors did not clearly explain the intention of the eyebrow depressor injection in all groups, which might factually influence the measured results of the eyebrow height if this was not performed.” The eyebrow depressors were injected concomitantly with the three forehead injection patterns because the purpose of our trial was to evaluate the effect of different forehead injections in the setting of a total upper face botulinum toxin treatment, as usually performed in clinical practice. The goal was not to evaluate the forehead injections alone but their effect on eyebrow height when all the other routine upper face botulinum toxin injections are done concomitantly. They also noted “the upper forehead horizontal injection […] was concurrently injected with lateral and medial eyebrow depressors. We are confused regarding the indications of this combined application for a young patient with only minimal wrinkles limited to the upper forehead.” We agree that not all young patients need concomitant eyebrow depressor injections for crow’s feet and/or glabella wrinkle treatment; however, we strongly advise the concomitant injection of the depressors to avoid eyebrow ptosis. We believe that the forehead should never be injected alone because even if eyebrow depressor injections are not indicated for treatment of wrinkles, they are always indicated to minimize eyebrow ptosis whenever the forehead is to be injected. They also stated that “eyebrow ptosis can generally be avoided by injecting no closer than 1 cm above the bony orbital rim in the midpupillary and using lower doses in the frontalis.” Although this is a common practice, we proved that lowering the injections to the mid forehead (even while staying 1 cm above the orbital rim) will undoubtedly result in eyebrow depression. Zhai and Qi also mentioned that: “we are puzzled regarding the reduced small doses just injected in the most cephalic part of the forehead for older patients; and if these patients’ cosmetic concern was brow elevation, they could be classified into the brow elevation without forehead lines treatment group.” We disagree with this statement, as those patients’ concern is mainly forehead wrinkles (even if they want to avoid eyebrow depression) and not the brow elevation alone without forehead wrinkle treatment, which is a different patient category in our algorithm. Concerning the mechanism of eyebrow height modification, Zhai and Qi concluded “it was not accurate to state that the avoided eyebrow depression resulted from residual lower frontalis contraction solely. The weakened depressors also contributed to the final results, which should not be neglected in the authors’ study.” We agree with them, as we stated in previous studies that three different mechanisms contribute to eyebrow height modification: (1) when the lateral depressor muscles are injected, selective paralysis of the depressors results in an unopposed elevation of the brow by the frontalis muscle; (2) when the medial depressor muscles are injected, the diffusion of the toxin into the medial frontalis fibers causes a partial paralysis of the medial frontalis and an increase in tone in the lateral frontalis fibers, resulting in elevation of the lateral brow; and (3) when the frontalis muscle is injected along with the eyebrow depressors, the potential eyebrow elevation by the frontalis is attenuated, resulting in a paradoxical depression of the eyebrows.2,3 In fact, in all three of these mechanisms, the frontalis is the main eyebrow elevator, and produces maximal effect when the antagonizing depressors are paralyzed. However, the opposite is not true; regardless of how much botulinum toxin is injected into the depressors, it will not result in eyebrow elevation if the frontalis is concomitantly paralyzed. Therefore, the elevation of the eyebrows is mainly caused by the frontalis contraction and not by the paralysis of the eyebrow depressors. We agree that this elevation will be maximal when the frontalis contraction is unopposed by the depressors. PATIENT CONSENT All participating patients gave written informed consent. DISCLOSURE None of the authors has a financial interest in any of the products, devices, or drugs mentioned in this communication. Samer Jabbour, M.D.Department of Plastic and Reconstructive Surgery Samer Jabbour, M.D.Department of Plastic and Reconstructive Surgery Marwan Nasr, M.D.Department of Plastic and Reconstructive SurgeryFaculty of MedicineSaint-Joseph UniversityBeirut, Lebanon