Layout 1 Thematic Section: Advances in Musculoskeletal and Neuromuscular Rehabilitation | Maccarone & Masiero Eur J Transl Myol 34 (4) 13162, 2024 doi: 10.4081/ejtm.2024.13162 PFP is caused by lesions of the facial nerve resulting in a complete denervation of facial muscles. Key pathologies associated with facial paralysis are the complete loss of movement in facial muscles, leading to immediate restrictions of mimic functionality, and the denervation atrophy, leading to a progressive loss of tone and deformation of facial symmetry. Patients suffer from cosmetical and functional losses but also negative perception of their body and social relationships.1 Being subject to difficulties expressing emotions non-verbally, they often feel to be perceived negatively by others. This leads to distress and possibly even depression, culminating in the withdrawal from social interactions.2 In addition, a complete loss of eye and mouth muscle tone may result on the functional level in severe constraints such as ulceration of the sclerae, eating or speaking impairments, restricted nasal ventilation, and reduced oral health.3 Whereas for many patients, surgical reinnervation proce- dures are the primary solution for an irreversible paralysis, even in these cases, a supportive treatment to bridge the time until reinnervation after surgery and reduce con- sequential damages is essential.4 As patients experience im- mense suffering in the context of this medical condition, non-invasive approaches need to be investigated in a way that complements surgical treatment options.2 Several studies show that FES is a non-invasive method to prevent atrophy in denervated muscles and improve facial appea- rance effectively.5,6 Some authors suggest electrical stimu- lation to be a suitable intervention; on one side for treating paralytic disorders of the central and peripheral nervous system and on the other side to prevent denervation atrophy Abstract Functional Electrical Stimulation (FES) is an established intervention for a range of muscular and neurological disorders that has already been studied in numerous publications. However, its ap- plication to Peripheral Facial nerve Paralysis (PFP) still needs to be sufficiently investigated. As the first approach known to the authors, this study examines the effect of FES on the facial muscles in complete PFP using ultrasonography as a means of observation. In a prospective single-center observational pilot study, ten patients with complete PFP, confirmed by needle-electromyography (EMG), performed FES of the affected lateral mouth region at home twice daily for 20 minutes. The facial muscles’ Cross-Sectional Area (CSA) was regularly assessed using sonographic quan- tification. While the CSA of most non-stimulated muscles decreased considerably during ongoing paralysis, a significant CSA increase of the Zygomaticus Muscle (ZYG), which was regularly subjected to FES, could be demonstrated. FES can halt the atrophy of denervated ZYG and po- tentially other facial muscles. Further investigations with a more significant patient collective are recommended. From now on, FES could be established as an additive method in the non-invasive treatment of PFP. Key Words: acial palsy, electrical stimulation, muscle ultrasound, denervated muscle. Eur J Transl Myol 34 (4) 13162, 2024 doi: 10.4081/ejtm.2024.13162 Deceleration of denervated facial muscle atrophy through functional electrical stimulation: a sonographic quantification in patients with facial nerve paralysis Gabriel Meincke,1 Johannes Krauß,1 Maren Geitner,1,2 Anna-Maria Kuttenreich,1,2 Dirk Arnold,1,2 Jonas Ballmaier,1,2 Thomas Lehmann,3 Winfried Mayr,4 Orlando Guntinas-Lichius,1,2,5 Gerd Fabian Volk1,2,5 1ENT-Department, Jena University Hospital, Jena, Germany; 2Facial-Nerve-Center, Jena University Hospital, Jena, Germany; 3Institute for Medical Statistics, Computer Science and Data Science, Jena University Hospital, Jena, Germany;4Center for Medical Physics and Biomedical Engineering, Medical University of Vienna, Vienna, Austria; 5Center of Rare Diseases, Jena University Hospital, Jena, Germany. This article is distributed under the terms of the Creative Commons Attribution Noncommercial License (CC BY-NC 4.0) which permits any noncommercial use, distribution, and reproduction in any medium, provided the original author(s) and source are credited. - 91 - Non -co mmerc ial us e o nly Deceleration of denervated facial muscle atrophy through functional electrical stimulation Eur J Transl Myol 34 (4) 13162, 2024 doi: 10.4081/ejtm.2024.13162 even in facial muscles.7,8 Even though FES is the subject of scientific controversy in terms of applicability and therapy adherence due to possible side effects such as pain, ery- thema and discomfort, there are studies indicating FES to be innocuous in patients with facial nerve paralysis.9,10 Ul- trasound (US) of facial muscles allows a reliable and easy- to-repeat quantification of facial muscle sizes.11 Furthermore, US is inexpensive, fast to perform, and a safe imaging method since it is radiation-free. It also produces high intra- and interrater reliability values.11 Therefore, this study aims to confirm that FES is indeed a suitable inter- vention to prevent muscle denervation atrophy associated with complete PFP by using a sonographic monitoring of facial muscles during FES. Materials and Methods Study design This prospective single-centre observational clinical study was registered in the German Clinical Trials Register (DRKS00015015) and approved by the local institutional ethics committee (no. 550503/18). Requirements for study inclusion were patients with a unilateral total PFP con- firmed by needle-EMG12,13, age of ≥18 years, mental and physical aptitude for home-based surface FES, and high motivation in participating in the clinical study. Exclusion criteria were pregnancy or breastfeeding, signs of reinner- vation in EMG, conservative treatment procedures (e.g. bot- ulinum toxin injections) or facial physiotherapy within the last 3 months, medical conditions that influence the results of the clinical investigations (e.g. general muscle diseases; epilepsy; skin diseases), known allergies or intolerances to materials used in the clinical trial, malignant or life-threat- ening diseases at the time of inclusion, bilateral paralysis, or central facial paralysis. Patients terminated the study after clinical signs of reinnervation, such as voluntary muscle tone of the affected side of the face, visible voluntary move- ment and visible synkinesis as well as serious adverse events, occurrence of malignant and life-threatening dis- eases or facial paralysis on the contralateral side as well as on patients’ demand. At the latest, the patients’ follow-up was terminated after one year of study inclusion. All pa- tients provided written informed consent prior to inclusion. Study protocol Ten patients were included. The baseline examination (T0) consisted of an EMG examination to verify complete uni- lateral PFP. US examination of the facial muscles was per- formed at every clinical visit (Table 1). The present investigation is focused on the results of the US examina- tions. The analyses of score-based paralysis evaluation and of portrait photography examinations will be published sep- arately.14 Follow-up visits (T2 to T52) took place in the hos- pital and the same procedure of the baseline examination. - 92 - Table 1. Schedule of visits and remote calls according to study protocol. Visit Remote call T. Time after EMG SFGS PROMs Photos US baselinein weeks* Baseline T 0 Yes Yes Yes Yes Yes 1 T 2R 2 Yes FU 1 T 4 4 Yes Yes Yes Yes Yes 2 T 6R 6 Yes FU 2 T 8 8 Yes Yes Yes Yes Yes 3 T 10R 10 Yes FU 3 T 12 12 Yes Yes Yes Yes Yes FU 4 T 16 16 Yes Yes Yes Yes Yes FU 5 T 20 20 Yes Yes Yes Yes Yes FU 6 T 28 28 Yes Yes Yes Yes Yes FU 7 T 40 40 Yes Yes Yes Yes Yes FU 8 T 52 52 Yes Yes Yes Yes Yes *At T2R and T4 a deviation ±1 week and from T6 to T52 of ±2 weeks were allowed; FU, follow up; EMG, needle electromyography; SFGS, Sunnybrook Facial Grading Score; PROMs, Patient Reported Outcome Measures: US, ultrasound. Non -co mmerc ial us e o nly Deceleration of denervated facial muscle atrophy through functional electrical stimulation Eur J Transl Myol 34 (4) 13162, 2024 doi: 10.4081/ejtm.2024.13162 Electrical stimulation protocol During the baseline examination, the FES parameters were determined in a comfortable sitting position with STMI- SOLA stimulator (BIOPAC Systems Inc., Germany). The STIWELL® med4 stimulation device (CE 0297; P/N 9001015) developed by MED-EL Elektromedizinische Geräte Gesellschaft m.b.H. (Innsbruck, Austria) was used for home training. Two adhesive electrodes (PALS® Neu- rostimulation electrodes, oval 4 cm x 6.4 cm, Axelgaard Manufacturing Co., Ltd., Lystrup, Denmark, CE-certified, REF 896230) were placed superficially over the ZYG on the affected side of the face. The cranial electrode was used as the cathode and the caudal electrode as the anode. Both electrodes were positioned as close as necessary to the cor- ner of the mouth to avoid stimulation of the surrounding muscles. Phase duration of 1, 2, 5, 10, 15, 25, 50, 100, 250, 500 and 1000 ms with increasing amplitudes in between 0.1 and 20 mA were then tested. Biphasic triangular and rectangular waveforms with a constant frequency of 1 Hz were used. Amplitudes were noted for each pulse length at which the ZYG contracted without pain and simultaneous stimulation of surrounding facial muscles. The parameters at maximum triggerable contraction below the pain thres- hold were then used to program the FES devices. To test tolerance, patients were stimulated for 20 minutes. Only the investigators were able to change stimulation settings by entering a password. The patients could not accidentally stimulate incorrectly or harm themselves. After the test stimulation, the patients were shown how to apply the electrodes correctly in front of a mirror and how to operate the FES device. Based on the clinically determined FES parameters, patients performed FES at home twice every day (morning and evening with an in- between break of at least 6 hours) for 20 min. For home training, a two-phase stimulation in a triangular wave- form with a phase duration of 5 seconds and a pulse pause of 1 second was performed.14 At each follow-up visit, the parameters and electrode positioning were ad- justed again to ensure optimal therapy success and pa- tient safety. On the day of the follow-up visit, only a single run of FES was performed at home. Patients ter- minated FES when EMG and clinical findings clearly in- dicated facial reinnervation. Facial electromyography and ultrasound examinations Standardised needle-EMG on frontalis (FRO), ZYG, orbic- ularis oculi (OOC) and oris (OOR) muscles13 were per- formed on the paralytic side of the face using VIASYSY Synergy (version 15.0. VIASYS Healthcare UK Ltd. War- wick, United Kingdom). The electrical activity of each muscle was monitored for denervation, synkinesis, and re- innervation. The US scanner MyLab Seven eHD Crystaline (Esaote, Italy) was employed with exclusive use of the linear trans- ducer SL1543 (18 Hz). An adapted version of an estab- lished sonography protocol covering mentalis (MEN), ZYG, depressor anguli oris (DAO), OOC, OOR and FRO muscles was put to use.15 US examination was used to quantify absolute and relative changes within the CSA parameter by which the muscle atrophy behaviour can be quantified.5,11 From this, con- clusions could be drawn about the effect of FES on the denervation atrophy of the mimic muscles. The CSA of the muscles provided a valuable indicator for the extent and development of both the atrophy and the muscle status. The assessment of the sonographic data was per- formed by employing the open-source image editing pro- gram ImageJ.16 Specific muscles were therefore encircled in a region of interest (ROI) for the automatic calculation of its CSA (Figure 1). - 93 - Figure 1. Example of graphic evaluation of ultrasound images using ImageJ: Determination of region of interest for a healthy depressor anguli oris muscle with automatic calculation of its cross-sectional area. Non -co mmerc ial us e o nly Deceleration of denervated facial muscle atrophy through functional electrical stimulation Eur J Transl Myol 34 (4) 13162, 2024 doi: 10.4081/ejtm.2024.13162 Statistics Linear mixed models were used to detect the significance of CSA value changes over time. Visit numbers were in- cluded as fixed effects as well as a random intercept for pa- tients in the model. Continuous values were summarised by mean and standard deviation or median and 25th/75th per- centile if the data was not normally distributed. All clinical visit values were analysed in pairwise comparison against Baseline visits. In addition, the data was analysed to detect significant value changes in the CSA for the whole period of investigation (pa). The significance level was set to p < 0.05. The assessed data was documented in Microsoft Excel (Version 2308. Microsoft Corp. Redmond, Wahington, USA) and statistical analysis was performed in IBM SPSS Statistics for Windows (Version 27.0. IBM Corp. Armonk, New York, USA). Statistical graphs were designed using GraphPad Prism (Version 10.2.1, GraphPad Software Inc., Boston, Massachusetts, USA). Results Patient characteristics Ten patients (median 61 years, 25th to 75th percentile 38.3 – 71 years; 4 female, 6 male, median time of denervation 130 d) underwent FES for a mean of 95 days (min. 35, max. 301). Facial paralysis etiologies were vestibular schwan- noma (n=3), parotid cancer (n=3), benign parotid tumor (n=1), chronic otitis media (n=1), zoster oticus (Ramsey- Hunt syndrome; n=1) and traumatic temporal bone fracture (n=1) (Table 2). None of the patients experienced any un- desired severe side effects of the FES. Minor side effects were skin irritation caused by the adhesive electrodes (n=1) and an unpleasant feeling (n=1). After T28 (28±2 weeks) all 10 patients had terminated the study either due to rein- nervation (n=6) or other termination criteria: stroke (n=1), long-term rehabilitation after total hip arthroplasty (n=1), metastasis of parotid carcinoma (n=1) and personal reasons (moved away; n=1). Muscular Cross Sectional Area (CSA) For a complete catalogue of all values obtained from the statistical analysis for CSA values, please refer to Table 3. No statistical significance for CSA value changes could be detected for any of the examined muscles when analysing the entire period of investigation (pa > 0.05). Mentalis muscle At the baseline visit, MEN showed a mean CSA of 27.9±3.2 mm². No significant CSA value change could be found over the entirety of the examination period (pa=0.976), and there were no significant CSA value changes in pairwise compa- rison. In absolute values, MEN’s CSA remained approx- imately constant. At T28, the CSA was 25.8±5.6 mm². - 94 - Table 2. Patients’ characteristics. ID Age Sex Etiology Palsy Reinnervation Termination Nerval Reason of (years) duration after 1 year after anastomosis termination (days)a surgery 1 51 M Vestibular schwannoma 118 Yes T8 None Reinnervation 2 24 F Parotid cancer 188 No T28 HFJA Personal reasons 3 64 M Chronic otitis media 48 No T12 None Stroke 4 77 F Zoster oticus 141 Yes T12 Reinnervation 5 61 F Vestibular schwannoma 383 Yes T28 HFJA Reinnervation 6 61 M Vestibular schwannoma 34 No T12 None Rehabilitation after THA 7 71 M Temporal bone fracture 58 Yes T4 None Reinnervation 8 71 M Parotid cancer 674 No T8 None Metastasis 9 30 M Benign parotid tumor 3 Yes T12 Great auricular Reinnervation nerve interposition 10 41 F Parotid cancer 1004 Yes T12 HFJA Reinnervation aclinical onset upon baseline visit; HFJA, hypoglossal-facial nerve anastomosis; THA, total hip arthroplasty; M, male; F, female. Non -co mmerc ial us e o nly Deceleration of denervated facial muscle atrophy through functional electrical stimulation Eur J Transl Myol 34 (4) 13162, 2024 doi: 10.4081/ejtm.2024.13162 - 95 - Ta bl e 3. S on og ra ph y re su lts o f C SA m ea su re m en t d ur in g el ec tr ic al st im ul at io n. T 0 T 4 T 8 T 12 B as el in e 4 ±1 w 8± 2 w 12 ±2 w M us cl e F pa n M ea n± SD n M ea n± SD p n M ea n± SD p n M ea n± SD p M en ta lis 0 .1 89 0. 97 6 1 0 27 .9 ±3 .2 9 2 6. 7± 3. 3 0. 68 6 6 2 6. 6± 3. 7 0. 71 0 3 2 4. 2± 4. 8 0. 42 7 O rb ic ul ar is o ris 1 .6 25 0. 19 5 1 0 27 .5 ±2 .9 9 2 6. 3± 3, .0 0. 53 3 6 2 1. 2± 3. 2 0. 01 2 3 2 6. 9± 3. 7 0. 83 4 D ep re ss or a ng ul i o ris 2 .1 39 0. 09 8 1 0 21 .7 ±3 .5 9 1 8. 5± 3. 6 0. 19 7 6 1 7. 2± 3. 9 0. 12 1 3 1 0. 1± 4. 6 0. 00 6 Zy go m at ic us 1 .5 44 0. 21 7 1 0 4 5. 5± 10 .2 9 54 .9 ±1 0. 4 0 .2 17 6 65 .4 ±1 1. 3 0 .0 31 3 52 .1 ±1 3. 4 0 .5 68 O rb ic ul ar is o cu li 2. 29 0 0. 08 0 1 0 7 .8 ±1 .4 9 6 .4 ±1 .4 0 .0 94 6 5 .0 ±1 .5 0 .0 06 3 4 .5 ±1 .7 0 .0 13 Fr on ta lis 0 .2 42 0. 95 7 1 0 50 .0 ±7 .9 9 5 4. 1± 8. 2 0. 57 7 6 4 8. 7± 9. 2 0. 87 3 3 52 .0 ±1 1. 7 0 .8 59 T 16 T 20 T 28 16 ±2 w 2 0± 2 w 2 8± 2 w M us cl e F pa n M ea n± SD p n M ea n± SD p n M ea n± SD p M en ta lis 0 .1 89 0. 97 6 2 2 4. 9± 5. 6 0. 58 2 2 2 8. 9± 5. 6 0. 85 3 2 2 5. 8± 5. 6 0. 69 4 O rb ic ul ar is o ris 1 .6 25 0. 19 5 2 2 8. 9± 4. 2 0. 70 2 2 2 6. 5± 4. 2 0. 77 7 2 2 4. 4± 4. 2 0. 39 2 D ep re ss or a ng ul i o ris 2 .1 39 0. 09 8 2 1 1. 4± 5. 1 0. 02 9 2 1 3. 7± 5. 1 0. 08 0 2 1 6. 9± 5. 1 0. 28 5 Zy go m at ic us 1 .5 44 0. 21 7 2 71 .7 ±1 5. 2 0 .0 62 2 68 .8 ±1 5. 2 0 .0 95 2 70 .4 ±1 5. 2 0 .0 75 O rb ic ul ar is o cu li 2. 29 0 0. 08 0 2 5 .9 ±1 .9 0 .1 91 2 5 .5 ±1 .9 0 .1 26 2 5 .3 ±1 .9 0 .0 99 Fr on ta lis 0 .2 42 0. 95 7 2 58 .7 ±1 3. 5 0 .5 10 2 61 .2 ±1 3. 5 0 .3 97 2 54 .0 ±1 3. 5 0 .7 62 pa , ov er al l s ig ni fic an ce fo r t he w ho le p er io d of in ve st ig at io n; M ea n, m ea n va lu es fo r c ro ss -s ec tio na l a re a [m m ²] ; S D , s ta nd ar d de vi at io n. Non -co mmerc ial us e o nly Deceleration of denervated facial muscle atrophy through functional electrical stimulation Eur J Transl Myol 34 (4) 13162, 2024 doi: 10.4081/ejtm.2024.13162 Orbicularis oris muscle At baseline visit, OOR produced a mean CSA of 27.5±2.9 mm². A significant CSA decrease in pairwise comparison was observed at T8 study visit (n=6; p=0.012). In terms of absolute values, there was a notable CSA decrease over the course of the study (Fig. 2). However, no significant CSA value changes for OOR were found over the whole ex- amination period (pa=0.195). At T28, the CSA was approx- imately 24.4±4.2 mm². Depressor anguli oris muscle At baseline visit, DAO produced a mean CSA of 21.7±3.5 mm². Significant CSA decreases in pairwise comparison were observed at study visits T12 (n=3; p=0.006) and T16 (n=2; p=0.029). In terms of absolute values too, a substan- tial CSA decrease was observed over the course of the study. However, no significant CSA value changes for DAO were detected over the whole examination period (pa=0.098). At T28, the CSA was approximately 16.9±5.1 mm². Zygomaticus muscle At baseline visit, ZYG, i.e. the muscle that was afterwards stimulated, produced a mean CSA of 45.5±10.2 mm². A sig- nificant CSA increase of 43.7 % in pairwise comparison was observed at T8 study visit (n=6; p=0.031). In absolute values, an overall increase of the CSA was observed over the course of the study (Figure 2). However, no significant CSA value changes were detected for ZYG when analysing the entirety of the examination period (pa=0.217). At T28, the CSA was 70.4±15.2 mm². Orbicularis oculi muscle At baseline visit, OOC produced a mean CSA of 7.8±1.4 mm². Significant CSA decreases in pairwise comparison were observed at study visits T8 (n=6; p=0.006) and T12 (n=3; p=0.013). Absolute values indicate a CSA decrease over the course of the study as well (Figure 2). However, no significant CSA value changes were found for OOC over the whole examination period (pa=0.080). At T28, the CSA was approximately 5.3±1.9 mm². Frontalis muscle At baseline visit, FRO produced a mean CSA of 50.0±7.9 mm². No statistical significance was found for FRO when analysing the whole examination period (pa=0.957), neither were there any significant CSA value changes in pairwise comparison. However, FRO produced slightly increasing CSA values over the course of the study in terms of absolute numbers. At T28, the CSA was approximately 54.0±13.5 mm². Discussion The applicability of sonography for the visualisation and examination of muscle condition like muscle atrophy is well known.11,17 This also applies to the mimic muscles being affected by facial nerve paralysis and the procedure has the advantages of being non-invasive, highly reprodu- cible, cost-effective and radiation-free.17 To the best of our knowledge, this study contains the very first approach to examining the effects of FES on patients with complete PFP by using facial muscle ultrasonography. FES had no harmful or detrimental effects on the facial muscles or patient well-being over the entire course of this study. None of the enrolled patients reported severe side ef- fects of the FES treatment. This finding is in accordance with many other studies which investigated electrical stim- ulation.7,9,10,14,18,19 Furthermore, several studies have de- scribed the suitability of FES for therapeutically addressing denervated or atrophied muscles.9,18,20,21 The academic con- cerns that have arisen to date regarding its applicability, harmlessness, therapeutic adherence and suitability for home training could be refuted in this three-part pilot study in collaboration with Krauß et al. as well as Volk et al.14,22 The advantages of the method outweigh the aforementioned reservations: Doucet et al. describe for skeletal muscles that FES can effectively increase muscle strength and blood flow, minimise muscle atrophy and partial recovery with healing/connective tissue as well as reduce pain.20 Arnold et al. substantiated the investigations regarding the appli- cability of the method to the facial muscles, particularly to ZYG, which was the target muscle of FES in this study. They outlined essential basic findings and instructions for use, which served as the basis for this pilot study.9 The objective of this work was to combine the application of ultrasound’s diagnostic suitability for measuring mimic muscles subjected to facial nerve paralysis17 with the ob- servation of these muscles during the course of the disease and the assessment of the influence of FES on them. In col- laboration with Krauß et al., a systematic investigation of FES on the denervated muscles was carried out using mul- tiple methods.14 In contrast to prior and similar studies such - 96 - Figure 2. Scatter dot plot visualising significant cross- sectional area changes for paralysed zygomaticus, orbic- ularis oculi and orbicularis oris muscles during FES at baseline and at T8 examinations. The asterisks indicate a statistically significant value change (p <0.05). For the zygomaticus, the plot visualises the increase in cross-sec- tional area found. For the other two muscles, their respec- tive reductions in cross-sectional area are shown. Non -co mmerc ial us e o nly Deceleration of denervated facial muscle atrophy through functional electrical stimulation Eur J Transl Myol 34 (4) 13162, 2024 doi: 10.4081/ejtm.2024.13162 as Tuncay et al. and Mäkelä et al. who stimulated multiple facial nerve-innervated mimic muscles, we focused on solely applying FES to the ZYG with regards to the pre- viously studied principles of Arnold et al. Compared to the default values for healthy ZYG muscles measured by Volk et al., there was identified a noticeably reduced CSA with a mean value of 45.5±10.2 mm² at baseline examination. Standard values for the muscle, on the other hand, are given as an average of 60-75 mm².11 A significant CSA increase was then found for the ZYG under FES during ongoing facial nerve paralysis in pair- wise comparison to the baseline examination. Conversely, significant CSA reductions of the DAO, OOR and OOC could be verified in pairwise comparison to the baseline examination, as would be expected in terms of a progres- sive atrophy of denervated muscles. This also confirms that a selective FES only targeting the ZYG was achieved without unintended stimulation of the other facial muscles examined. Based on the study inclusion criterion of complete unilateral PFP and the resulting absence of voluntary residual nerve activity, the presented results impressively demonstrate that FES is capable of halting and even reversing the atrophy of denervated mimic muscles. First results could already be identified within 4-8 weeks after the start of stimulation, shown here for the ZYG (Table 3). That general finding is consistent with those of other studies that used different methods than US to quantify the muscle condition. In their study, Mäkelä et al. examined facial palsy patients in the chronic phase of the disease, assuming both completely as well as incompletely denervated facial muscles and ad- ditionally applying FES to the FRO, OOC and OOR mus- cles. According to their results, they describe that FES has the potential for restoring function of the stimulated facial muscles in facial nerve palsies, even if it had been persistent for several years.7 Tuncay et al. in turn examined patients in the acute phase of facial nerve palsy, assuming com- pletely and incompletely denervated muscles as well, and came to the conclusion that the addition of FES to conven- tional therapeutic approaches such as physiotherapy is su- perior to omitting this method during the early stages of the disease.18 Within the framework of this pilot study, Krauß et al. as- sessed functional-objective changes in the mimics of the same facial nerve paralysis patients using photographic analysis among other methods. Both this work along with Krauß et al. obtained compatible results while applying dif- ferent approaches: For example, the shown substantial CSA decrease of the non-stimulated OOC is consistent with the increase of Krauß et al.’s so-called palpebral fissure height parameter,14 since the functional-structural impairment of the OOC in the lower eyelid caused by atrophy22 should in- crease said value. The same applies to the CSA increase of the ZYG as an important smile muscle and the increase in the smile angle parameter14 used by Krauß et al. to quantify the ability to smile. The exclusive recruitment of patients with complete PFP allowed us to examine the isolated effect of FES on the af- fected muscles without any influence from voluntary resid- ual nerve activity. However, this strict inclusion criterion significantly reduced the number of participants, making it challenging to draw conclusions applicable to a larger pa- tient population. This is generally shown by the results of the statistical data evaluation: numerous significant findings for CSA value changes could be observed accordingly in pairwise analyses to the Baseline examination (OOR, DAO, ZYG, OOC). However, statistical significance over the en- tire examination period could not be established for any of the muscles’ CSA value changes despite the promising trends. Very likely, significance could have been gained with a larger sample size. This pilot study, along with the complementary work by Krauß et al. and Volk et al., primarily focused on asses- sing the feasibility and tolerability of FES, as well as as- sessing its impact on denervated facial muscles by performing US measurements (Volk G, Thielker J, Ar- nold D, et al. Selective electrostimulation of the zygo- maticus major muscle for the treatment of facial paralysis: stimulation parameters, 2024. Personal com- munication).14 Given these aims, the small number of re- cruitable subjects as well as for practicality purposes, the decision was made during the early planning phase not to include a control group or blinding. To further confirm the causal relationship between FES and improvements in muscle function, facial movement, and the reduction of atrophy in denervated facial muscles, such procedures will be essential to implement in future research. The au- thors believe the lack of statistical significance in CSA muscle value changes when analysing the entirety of the examination period is mainly due to the limited sample size, the study’s design as a pilot or feasibility study lacking a control group and blinding, and possibly also the exclusive use of examiner-dependent imaging. While US has strong intra- and interrater reliability, it is ex- aminer-dependent, unlike stationary imaging techniques such as Magnetic Resonance Imaging (MRI), and thus more prone to variability. It is possible that minor value scattering may have occurred and that, combined with the aforementioned factors, could have biased the statis- tical outcomes. As a result, future studies could ad- ditionally incorporate MRI to assess the affected facial muscles. This approach, with the additional use of MRI measurements of the mimic muscles, was investigated and recommended, for instance, by Mastryukova et al. in 2020.23 Despite the outlined limitations, the findings from this study provide a promising outlook for the non- invasive treatment of PFP by applying FES and offer valuable insights for designing future studies, which should ideally include a multi-centre, double-blind ap- proach with a control group. Conclusions Within the limits of study design, it was demonstrated that FES has great potential to halt and even reverse the atrophy of denervated mimic muscles in facial nerve paralysis pa- tients. It is recommended that the procedure be subjected to further investigations based on this pilot study with a larger patient collective and adapted study design. Looking ahead, FES offers a promising prospect of being established - 97 - Non -co mmerc ial us e o nly Deceleration of denervated facial muscle atrophy through functional electrical stimulation Eur J Transl Myol 34 (4) 13162, 2024 doi: 10.4081/ejtm.2024.13162 as an additional therapeutic pillar in the conservative treat- ment of facial nerve paresis and paralysis. Furthermore, the method of US quantification of the effect of FES on the de- nervated muscles by measuring the muscle CSA parameter is considered to be well suited and applicable in this context. List of acronyms CSA, cross sectional area DAO, depressor anguli oris muscle EMG, electromyography FES, functional electrical stimulation FRO, frontalis muscle (venter frontalis MO, musculi occipitofrontalis) MEN, mentalis muscle MRI, magnetic resonance imaging OOC, orbicularis oculi muscle OOR, orbicularis oris muscle PFP, peripheral facial nerve paralysis US, ultrasound ZYG, zygomaticus major muscle Contributions GFV, DA, and WM oversaw planning and designing the study. OGL contributed to the study’s funding and helped with interpreting the data. The tasks of recruiting patients, collecting ratings and scores, conducting EMG, and adjust- ing the stimulation parameters during clinical visits were primarily handled by MG, AMK, JB, DA, GFV, OGL, JK, and GM. MG, AMK, JK, and GM were responsible for data collection and digitization. JK and GM conducted the ul- trasound examinations. JK, GM, and TL compiled the sta- tistical analysis. JK and GM also created the digital graphics. GM wrote the article in close collaboration with all co-authors. Conflict of interest Authors GM, JK, MG, AMK, DA, OGL and GFV have re- ceived financial support from MED-El, Innsbruck, Austria. OGL was supported by a grant from the DFG (GU-463/12- 1) and MG received a grant from the Interdisciplinary Center for Clinical Research. The remaining authors have no conflicts of interest. Ethics approval This prospective single-centre observational clinical study was registered in the German Clinical Trials Register (DRKS00015015) and approved by the local institutional ethics committee (no. 550503/18). Acknowledgements We sincerely thank Martin Heinrich for his continuous tech- nical support and his willingness to assist with technical challenges and solutions. Corresponding author Gabriel Meincke, ENT Department, Jena University Hos- pital, Am Klinikum 1, 07747 Jena, Germany- ORCID ID: 0009-0009-9960-9783 E-mail: gabriel.meincke@uni-jena.de Johannes Krauß ORCID ID: 0009-0004-6929-2694 johannes.krauss@uni-jena.de Maren Geitner ORCID ID: 0009-0002-3688-2853 maren.geitner@med.uni-jena.de Anna-Maria Kuttenreich ORCID ID: 0000-0002-4508-5402 anna.kuttenreich@rwth-aachen.de Dirk Arnold ORCID ID: 0000-0001-8089-3934 dirk.arnold@med.uni-jena.de Jonas Ballmaier ORCID ID: 0000-0003-3051-2835 jonas.ballmaier@med.uni-jena.de Thomas Lehmann ORCID ID: 0000-0003-1104-7923 thomas.lehmann@med.uni-jena.de Winfried Mayr ORCID ID: 0000-0001-9648-3649 winfried.mayr@meduniwien.ac.at Orlando Guntinas-Lichius ORCID ID: 0000-0001-9671-0784 orlando.guntinas@med.uni-jena.de Gerd Fabian Volk ORCID ID: 0000-0003-1245-6331 fabian.volk@med.uni-jena.de References 1. Guerreschi P, Labbé D. Sequelae of facial palsy: a com- prehensive treatment. Plastic Reconstr Surg 2019;144: 682e-92e. 2. Dobel C, Miltner WHR, Witte OW, et al. Emotionale Auswirkungen einer Fazialisparese. Laryngorhinootol- ogie 2013;92:9-23. 3. Strobelt L, Kuttenreich A-M, Volk GF, et al. Oral health and oral health-related quality of life in pa- tients with chronic peripheral facial nerve palsy with synkineses—A case-control-study. PLoS One 2022; 17:e0276152. 4. Kurz A, Volk GF, Arnold D, et al. Selective electrical surface stimulation to support functional recovery in the early phase after unilateral acute facial nerve or vocal fold paralysis. Front Neurol 2022;13:869900. - 98 - Non -co mmerc ial us e o nly mailto:gabriel.meincke@uni-jena.de mailto:johannes.krauss@uni-jena.de mailto:maren.geitner@med.uni-jena.de mailto:anna.kuttenreich@rwth-aachen.de mailto:dirk.arnold@med.uni-jena.de mailto:jonas.ballmaier@med.uni-jena.de mailto:thomas.lehmann@med.uni-jena.de mailto:winfried.mayr@meduniwien.ac.at mailto:Orlando.Guntinas@med.uni-jena.de mailto:fabian.volk@med.uni-jena.de Deceleration of denervated facial muscle atrophy through functional electrical stimulation Eur J Transl Myol 34 (4) 13162, 2024 doi: 10.4081/ejtm.2024.13162 5. Bersch I, Fridén J. Electrical stimulation alters muscle morphological properties in denervated upper limb muscles. EBioMedicine 2021;74. 6. Kern H, Salmons S, Mayr W, et al. Recovery of long- term denervated human muscles induced by electrical stimulation. Muscle & Nerve 2005;31:98-101. 7. Mäkelä E, Venesvirta H, Ilves M, et al. Facial muscle reanimation by transcutaneous electrical stimulation for peripheral facial nerve palsy. J Med Eng Technol 2019;43:155-64. 8. Bersch I, Mayr W. Electrical stimulation in lower mo- toneuron lesions, from scientific evidence to clinical practice: a successful transition. Eur J Transl Myol 2023;33:11230. 9. Arnold D, Thielker J, Klingner CM, et al. Selective Sur- face Electrostimulation of the Denervated Zygomaticus Muscle. Diagnostics (Basel) 2021;11(2). 10. Puls WC, Jarvis JC, Ruck A, et al. Surface electrical stimulation for facial paralysis is not harmful. Muscle Nerve 2020;61:347-53. 11. Volk GF, Sauer M, Pohlmann M, Guntinas-Lichius O. Reference values for dynamic facial muscle ultraso- nography in adults. Muscle Nerve 2014;50:348-357. 12. Guntinas-Lichius O, Volk GF, Olsen KD, et al. Facial nerve electrodiagnostics for patients with facial palsy: a clinical practice guideline. Eur Arch Otorhinolaryngol 2020;277:1855-74. 13. Geißler K, Guntinas-Lichius O, Fabian Volk G. [Needle electromyography of facial muscles]. Laryngorhinoot- ologie 2016;95:528-9. 14. Krauß J, Meincke G, Geitner M, et al. Efficacy of elec- trical stimulation of the zygomaticus muscle in com- plete facial paralysis: evidence from facial grading and automated image analysis. Eur J Transl Myol 2024, in press. 15. Sauer M. Instructions for sonography of the facial mus- cles/Anleitung zur Sonographie der mimischen Musku- latur. Jena, 2013. 16. Schneider CA, Rasband WS, Eliceiri KW. NIH Image to ImageJ: 25 years of image analysis. Nature Methods 2012;9:671-5. 17. Volk GF, Pohlmann M, Sauer M, et al. Quantitative ul- trasonography of facial muscles in patients with chronic facial palsy. Muscle Nerve 2014;50:358-65. 18. Tuncay F, Borman P, Taşer B, et al. Role of electrical stimulation added to conventional therapy in patients with idiopathic facial (Bell) palsy. Am J Phys Med Re- habil 2015;94:222-8. 19. Hyvärinen A, Tarkka IM, Mervaala E, et al. Cutaneous electrical stimulation treatment in unresolved facial nerve paralysis: an exploratory study. Am J Phys Med Rehabil 2008;87:992-7. 20. Doucet BM, Lam A, Griffin L. Neuromuscular electri- cal stimulation for skeletal muscle function. Yale J Biol Med 2012;85:201-15. 21. Boncompagni S, Kern H, Rossini K, et al. Structural differentiation of skeletal muscle fibers in the absence of innervation in humans. Proc Natl Acad Sci U S A 2007;104:19339-44. 22. Radnót M, Follmann P. Ultrastructural changes in senile atrophy of the orbicularis oculi muscle. Am J Ophthal- mol 1974;78:689-99. 23. Mastryukova V, Arnold D, Güllmar D, et al. Can MRI quantify the volume changes of denervated facial mus- cles? Eur J Transl Myol 2020;30:8918. Disclaimer All claims expressed in this article are solely those of the authors and do not necessarily represent those of their af- filiated organizations, or those of the publisher, the editors and the reviewers. Any product that may be evaluated in this article or claim that may be made by its manufacturer is not guaranteed or endorsed by the publisher. Submitted: 25 September 2024. Accepted: 3 October 2024. Early access: 13 November 2024. - 99 - Non -co mmerc ial us e o nly