Background: Complications, such as eyelid ptosis, have been attributed to botulinum toxin type A. An "hourglass" deformity, which is the consequence of temporalis muscle atrophy, has not been reported previously.
Objective: To report a transient muscle deformity of the temporalis muscle caused by botulinum toxin type A.
Methods: Patients who underwent injection of 25 units of botulinum toxin type A into the temporal muscle, in a fan-shaped fashion, during an ongoing study for treatment of migraine were noted to develop temporary depression of the temples. Preinjection and postinjection photographs were taken. Patients were also sent questionnaires to verify the observed information.
Results: Only 26 of 92 patients who underwent injection of botulinum toxin type A into the temporalis muscle subsequently reported depression of the muscle. When examined, all 92 patients exhibited this deformity ranging from minimal to significant. Patients who seemed to have less deformity were those who had excessive soft tissue overlying the muscle due to excess weight.
Conclusion: A newly recognized deformity is reported subsequent to the injection of botulinum toxin type A into the temporalis muscle. Informing patients of this transient deformity may minimize concern following treatment.