Clinical and electrophysiological studies of botulinum toxin type A to treat hemifacial spasm complicated with auricular symptoms

Objective: To investigate the involvement of posterior auricular muscle (PAM) and the effect of botulinum toxin type A (BTX-A) injection into PAM in patients with hemifacial spasm (HFS) complicated with auricular symptoms.

Methods: Sixty-three consecutive HFS patients complicated with auricular symptoms such as tinnitus or murmur, "ticking" or a "clicking" sound and discomfort on the same side, who were referred to our department between July 2009 and January 2010, were enrolled. The diagnosis of idiopathic HFS was made clinically. The patients were largely randomized into two BTX-A treatment groups according to the order of referral. The first group included 33 cases where the injection sites were routinely located at the frontal, orbicularis oculi, zygomaticus and buccinator muscles while the other was the PAM group, which included 30 cases, where 4 units of BTX-A were additionally injected into the PAM prior to injection at other sites. A test of blink reflex was performed and the lateral spread of blink reflex to the orbicularis oris (OO) and PAM, i.e. abnormal muscle response (AMR), was recorded and the peak-peak amplitude of AMR was measured. The patients were followed up clinically and electrophysiologically for at least 4 weeks (29.47 ± 2.53 days).

Results: 1) Before injection, the latencies of R1, R2, R2' were normal, there was no significant difference between uninjured and affected side; The amplitudes of R1, R2, R2' in affected side were higher. 2) After injection, there was no significant change of the R1, R2 and R2' latencies; The amplitudes of R1, R2 and R2' decreased significantly. 3) Patients reported that their auricular symptoms subsided after injection in both groups; The remission rate was 45.5% (15/33) and 76.7% (23/30) in the regular and PAM group, respectively, with a higher rate in the PAM group (χ(2) = 6.40, P = 0.011). 4) In both groups the AMR amplitude decreased significantly after injection. In the regular group, the respective OO amplitudes (μV) before and after injection were 304.00 ± 30.34 and 129.33 ± 9.59 (t = 5.820, P = 0.000), and for PAM the amplitudes were 298.00 ± 33.28 and 184.67 ± 20.21 (t = 2.818, P = 0.014); in the PAM group, the before and after injection OO amplitudes were 405.33 ± 66.71 and 116.00 ± 9.99 (t = 4.214, P = 0.001), and for PAM they were 390.00 ± 53.58 and 72.00 ± 9.67 (t = 6.011, P = 0.000), respectively. 5) PAM amplitudes in the PAM group decreased more significantly after BTX-A injection compared with those in the regular group (t = 4.237, P = 0.001).

Conclusions: The treatment on HFS with local injection of BTX-A is very effective. In HFS complicated with auricular symptoms patients, electrophysiological studies are helpful for guiding treatment plans, and the auricular symptoms could be improved by BTX-A injection into the PAM in addition to the regular injection sites.