Effective botulinum toxin injection point for treatment of headache

Abstract

The underlying causes of migraine are often nerve and muscle disorders, which has led to botulinum toxin type A (BoNT-A) injection gaining traction as a viable treatment option. However, previous injection sites on the temporalis muscle for treating migraine were determined by observing the trigger point of migraines, and it is unsure whether these are the most anatomically effective sites for injection (Whitcup et al., 2014).

This study performed an extensive analysis of published research on the morphology of the temporalis muscle in order to provide an anatomical guideline on how to distinguish the temporalis muscle and temporalis tendon by observing the surface of the patient’s face. Furthermore, it was found that Sihler’s staining could be applied to the temporalis muscle in order to identify accurate and effective BoNT-A injection sites for treating migraines.

Twenty-one hemifaces of cadavers (16 males, 5 females; mean age, 81.0 years; age range, 63？93 years) were used in this study. The experiment was divided into two steps: (1) morphologically analyzing the temporalis region of the cadavers and (2) applying Sihler’s staining to the temporalis muscle and tendon.

The posterior border of the temporalis tendon was classified into three types according to its location relative to five reference lines: in Type I the posterior border of the temporalis tendon is located in front of reference line L2 (4.8%, 1/21), in Type Ⅱ it is located between reference lines L2 and L3 (85.7%, 18/21), and in Type Ⅲ it is located between reference lines L3 and L4 (9.5%, 2/21).

The vertical distances between the horizontal line passing through the jugale (LH) and the temporalis tendon along each of reference lines L0, L1, L2, L3, and L4 were 29.74±6.87 mm (mean±SD), 45.06±8.84 mm, 37.76±11.18 mm, 42.50±7.59 mm, and 32.14±0.47 mm, respectively; the corresponding vertical distances between LH and the temporalis muscle were 55.02±8.25 mm, 74.99±9.90 mm, 73.97±10.12 mm, 55.24±13.25 mm, and 47.56±11.41 mm.

Sihler’s staining shows that the anterior and posterior branches of the deep temporal nerve run through the anterior and posterior fibers of the temporalis muscle, respectively.

BoNT-A should be injected into the temporalis muscle at least 45 mm vertically above the zygomatic arch. This will ensure that the muscle region is targeted and so produce the greatest clinical effect with the minimum concentration of BoNT-A. In order to easily identify the temporalis muscle in a clinical setting, the second finger should be placed on the bottom corner of the zygomatic arch; the tip of the thumb will then be located 45 mm from the zygomatic arch.