An unusual adverse event of botulinum toxin injection in the lower face

Background In the lower third of the face, botulinum toxin A is used to obtain a more harmonious contour. The anatomical complexity of the face requires a more precise application of botulinum toxin. Aim Describe the treatment of an unexpected effect after botulinum toxin A application in the lower third of the face. Patient/Methods A 51‐year‐old female patient presented to our clinic for application of botulin toxin aiming to improve facial wrinkles and contour. 50 U of botulinum toxin type A were applied to the upper third and 20 U to the lower third of the face. The patient returned after 10 days with a smile asymmetry and an excessive and unconscious lowering on the right side of the lower lip while laughing. So, 3 U of botulinum toxin were applied to the center of the depressor labii inferioris muscle on the right side. Results The patient returned with a satisfactory correction of the smile asymmetry. Conclusion Although treatments with botulinum toxin A are considered safe, unexpected results can occur. In our case, it probably occurred due to medial injection or diffusion of botulinum toxin A into depressor anguli oris muscle on the left side that may lead to paralysis of the left depressor labii inferioris muscle and downward hyperfunction of the unaffected right lower lip. The correction was made with a new injection of botulinum toxin A in the depressor labii inferioris hyperactive muscle at the right side.