Selective surface electrostimulation of the synkinetic zygomatic muscle with ball electrodes

Introduction We assessed the possibility to selectively stimulate a synkinetically reinnervated zygomatic muscle (ZYG) without eliciting specific contractions of other facial muscles in patients with postparalytic facial synkinesis (PFS). Such idea could support the development of active stimulation implants for patients suffering from PFS.

Methods 10 patients were recruited, suffering from PFS with varying degrees of ZYG synkinesis. Onset period differed from patient to patient. Each patient underwent the 1 Hz test stimulation a single time with STMIsola (BIOPAC Systems, Inc. Germany) using triangular and rectangular pulses. 2 ball electrodes were placed over the ZYG close to the mouth corner and slowly moved along its anatomical course until no selective stimulation was possible.

Results Selective ZYG stimulation was achieved over a 4.5x3 cm area close to the mouth corner. The most effective pulse width (PW) was 100 or 250 ms with triangular and 1 s with rectangular pulses. Amplitudes in the range of 3-6 mA delivered best results with all assessed PWs except the very short 1 ms, for witch a range between 7 and 10 mA was needed. Few patients reached the discomfort threshold or showed a specific facial muscle response (e.g. masseter muscle) before a selective ZYG stimulation could be achieved.

Conclusions: Selective stimulation of synkinetically reinnervated ZYG is achievable as long as parameters are accurately assessed and the stimulation is delivered on the target muscle. Although encouraging these preliminary results should be further confirmed for the development of implants to restore facial symmetry in patients with PFS.

Conflict of Interest Der Erstautor weist auf folgenden Interessenkonflikt hin MED-EL Elektromedizinische Geräte GmbH, Innsbruck, Österreich

Conflict of Interest

The author declares that there is no conflict of interest.

Publication History

Article published online:
24 May 2022