Altered facial muscle innervation pattern in patients with postparetic facial synkinesis

Abstract

Objectives/Hypothesis: Using surface electrostimulation, we aimed to use facial nerve mapping (FNM) in healthy subjects and patients with postparetic facial synkinesis (PPFS) to define functional facial target regions that can be stimulated selectively.Study Design: Single-center prospective cohort study. Methods: FNM was performed bilaterally in 20 healthy subjects and 20 patients with PPFS. Single-pulse surface FNM started at the main trunk of the facial nerve and followed the peripheral branches in a distal direction. Stimulation started with 0.1 mA and increased in 0.1 mA increments. The procedure was simultaneously video recorded and evaluated offline.Results: A total of 1,873 spots were stimulated, and 1,875 facial movements were evaluated. The stimulation threshold was higher on the PPFS side (average = 9.8 AE 1.0 mA) compared to the contralateral side (4.1 AE 0.8 mA) for all stimulation sites or compared to healthy subjects (4.1 AE 0.5 mA; all P < .01). In healthy subjects, selective electrostimulation AE one unintended coactivation was possible at all sites in >80% of cases, with the exception of pulling up the corner of the mouth (65%-75%). On the PPFS side, stimulation was possible for puckering lips movements in 60%/75% (selective stimulation AE one coactivation, respectively), blinking in 55%/80%, pulling up the corner of the mouth in 50%/85%, brow raising in 5%/85, and raising the chin in 0%/35% of patients, respectively.Conclusions: FNM mapping for surgical planning and selective electrostimulation of functional facial regions is possible even in patients with PPFS. FNM may be a tool for patient-specific evaluation and placement of electrodes to stimulate the correct nerve branches in future bionic devices (e.g., for a bionic eye blink).

Tolerability of facial electrostimulation in healthy adults and patients with facial synkinesis

“…The range to the tolerability threshold was high: Depending on the pulse duration, average stimulation intensities of up to 24-30 mA (for very short pulses of 0.1 ms duration) to 5-7 mA (for pulses of 50 ms duration) were with tolerable discomfort. As it has already been shown for surface facial nerve mapping, the stimulation thresholds were higher in patients with postparetic facial synkinesis than in healthy persons [3]. This could be explained by a disturbed myelinization of the reinnervated axons causing a higher motor threshold.…”

“…Related to the question of optimal stimulation from a functional point of view, is the sometimes asserted that electrostimulation in the face is limited by its low tolerance to electricity, especially in patients with facial palsy. From surface facial nerve mapping to detecting the course of peripheral facial nerve branches, we only know that the stimulation thresholds are higher in patients with postparetic facial synkinesis than in healthy persons [3]. Therefore, it is necessary to combine investigations on the efficacy of facial electrostimulation with pain or comfort ratings of the patients [4].…”

Continual rehabilitation motivation of patients with postparalytic facial nerve syndrome

“…The present study analyzed the data of the patients with (PFS) at the time of the survey. The criteria were as follows: (a) a unilateral peripheral facial palsy; (b) incomplete recovery, (c) interval between onset and assessment at least 6 months; (d) at least one facial electromyography (EMG) confirming a PFS including synkinetic activity between periocular and perioral facial muscles [ 1 , 13 ]. 204 of the contacted 300 patients fulfilled these PFS criteria (69 answered, 135 did not answer; response rate of PFS patients: 33.8%).…”

“…Severe facial nerve paralysis can lead in the chronic phase to altered patterns of muscle contraction and postparetic facial synkinesis (PFS). PFS is a disfiguring condition characterized by involuntary contraction of one or more facial muscles during voluntary movement of other muscles [ 1 , 2 ]. Diminished facial expression, especially the inability to smile and affected face-to-face communication are the major non-motoric disabilities [ 3 ].…”

Facial nerve electrodiagnostics for patients with facial palsy: a clinical practice guideline

“…Nevertheless, as part of preoperative work-up FNM has so far mainly been established before surgery of vascular malformations [49]. FNM helps to map the course of the peripheral facial nerve and its fine peripheral branches in patients with tumor or scar around the facial nerve [50].…”