The blink reflex and its modulation - Part 2: Pathophysiology and clinical utility

The blink reflex (BR) is integrated at the brainstem; however, it is modulated by inputs from various structures such as the striatum, globus pallidus, substantia nigra, and nucleus raphe magnus but also from afferent input from the peripheral nervous system. Therefore, it provides information about the pathophysiology of numerous peripheral and central nervous system disorders. The BR is a valuable tool for studying the integrity of the trigemino-facial system, the relevant brainstem nuclei, and circuits. At the same time, some neurophysiological techniques applying the BR may indicate abnormalities involving structures rostral to the brainstem that modulate or control the BR circuits. This is a state-of-the-art review of the clinical application of BR modulation; physiology is reviewed in part 1. In this review, we aim to present the role of the BR and techniques related to its modulation in understanding pathophysiological mechanisms of motor control and pain disorders, in which these techniques are diagnostically helpful. Furthermore, some BR techniques may have a predictive value or serve as a basis for follow-up evaluation. BR testing may benefit in the diagnosis of hemifacial spasm, dystonia, functional movement disorders, migraine, orofacial pain, and psychiatric disorders. Although the abnormalities in the integrity of the BR pathway itself may provide information about trigeminal or facial nerve disorders, alterations in BR excitability are found in several disease conditions. BR excitability studies are suitable for understanding the common pathophysiological mechanisms behind various clinical entities, elucidating alterations in top-down inhibitory systems, and allowing for follow-up and quantitation of many neurological syndromes.

Blink reflex excitability in patients with Hemifacial spasm exhibiting different abnormal discharge patterns: from early isolated discharges to later grouped bursts or tonic spasms

OBJECTIVE

We studied blink reflex (BR) and BR excitability recovery (BRER) in patients with hemifacial spasm (HFS) exhibiting different abnormal discharge patterns. We hypothesized that patients with groups of clonic or tonic burst activities appear later in the disease course and may have more excitability of the BR circuit at the brainstem compared to patients with isolated twitchings, which occur earlier.

METHODS

We included 124 patients with botulinum toxin-naive HFS (mean age 50.6 ± 13.3 years) and 40 healthy subjects. We performed surface polymyography on facial muscles in patients and classified them according to the abnormal discharge pattern: isolated discharges, grouped bursts forming random sequences, tonic spasms, and a combination of these activities. Then, we recorded BR and BRER at 200, 600, and 1000 ms interstimulus intervals. We compared disease duration, R1 and R2 latencies, R2 area-under-the-curve (AUC), and BRER% (i) between healthy subjects and patients and (ii) among groups of patients with different abnormal discharge patterns.

RESULTS

There were isolated discharges in 28 patients, grouped bursts forming random sequences in 42, and continuous muscle activity with tonic spasms in one. The remaining patients had combinations. Mean R1 and R2 latencies were significantly longer, and mean R2 AUC was significantly higher on the symptomatic side of patients compared to healthy subjects. The mean BRER was enhanced on both sides in patients than in healthy subjects (p < 0.001). However, it was similar among patient groups with different abnormal discharge patterns (p > 0.05). The mean disease duration in patients with isolated discharges was shorter (3.3 ± 2.0 years) than those with grouped bursts or tonic spasms (p = 0.002; Kruskal-Wallis test).

CONCLUSION

Our study observed that excitability at the brainstem was similar in HFS patients with different abnormal discharge patterns, suggesting that the difference in discharge patterns in HFS may be due to a reason other than the difference in BR excitability.

Patient-reported outcomes following a break in ophthalmic botulinum toxin therapy during the COVID-19 pandemic

OBJECTIVE

To evaluate the effect of a break in botulinum toxin treatment, necessitated by the COVID-19 pandemic, on patients' quality of life.

METHODS

Prospective cohort study of all patients undergoing incobotulinumtoxinA treatment in our department-for benign essential blepharospasm (BEB), hemifacial spasm (HFS), aberrant facial regeneration (AFR), or crocodile tears-who were affected by the break in service (March 18, 2020-June 17, 2020). All patients who received treatment both before and after the break in service were included. Data gathered included subjective patient-reported measure of "time until treatment failure" and disease rating scale scores: Blepharospasm-Dystonia Functional Disability Assessment Scale (BDFDAS; for BEB, HFS, and AFR); Jankovic Rating Scale (JRS; for BEB and HFS); and TEARS Epiphora Grading Scale (for crocodile tears).

RESULTS

Across 72 patients, there was a mean treatment delay of 3.9 months (range, 0-9.8 months). After a period of effect, treatment failed in all patients, with a mean time until treatment failure of 3.9 months (range, 0.5-12.0 months). All patient-reported outcome measurements increased, with greatest effect seen in AFR (178% increase in BDFDAS) and BEB (41% increase in JRS). At least 2 patients sought and underwent retreatment elsewhere in the private sector because of their symptom severity.

CONCLUSIONS

Patients with AFR and BEB are likely to tolerate a break in service least, whereas patients with crocodile tears appear to be less affected. This real-world snapshot allows quantification of the harm caused by a break in botulinum toxin service or a treatment delay. This study provides valuable information should further breaks in service or treatment delay be considered in the future due to a further wave of COVID-19 or other reasons.

[Microvascular Decompression:The Superiority of Transposition]

In this feature article, we underscore the advantages of Transposition over Interposition in the management of trigeminal neuralgia and hemifacial spasm. Interposition, while effective, has raised concerns owing to long-term complications associated with the use of artificial materials, such as Teflon and silicone sponges. Transposition, on the other hand, mitigates these issues, showcasing adaptability to a range of anatomical and pathological conditions and affirming its standing as a safer and more effective treatment alternative. Each technique has distinct applications that are governed by the patient's specific anatomical and pathological needs. While Transposition is emerging as a favored option, Interposition remains relevant in specific cases, underscoring the necessity for a personalized approach to neurovascular decompression. In offering a comprehensive overview, this article is not just an academic exercise, but also a practical resource. A nuanced exploration of these surgical interventions is meant to provide readers with actionable insights, blending the current findings with real-world applicability. The goal is to foster a deeper understanding and aid practitioners in making informed decisions that are finely attuned to each patient's unique needs and conditions, ensuring optimal outcomes, while prioritizing safety and effectiveness.

Facial phantom model: a low-cost and safe tool for teaching botulinum toxin application in neurology residencies

BACKGROUND

 The application of botulinum toxin (BoNT) in the treatment of blepharospasm and hemifacial spasm (HS) is a well-established practice. However, neurology residency programs often rely on real patients for training, which has limitations in terms of patient availability and skill acquisition.

OBJECTIVE

 Assess the efficacy of a new facial phantom model for acquiring motor skills in BoNT application.

METHODS

 An anthropomorphic facial phantom model was developed in collaboration with a medical training simulator start-up. A group of seven neurologists and one ophthalmologist with expertise in BoNT application evaluated the model using an adapted learning object review instrument (LORI). The instrument assessed aspects such as: content quality, alignment of learning objectives, feedback and adaptation, motivation, presentation design, and accessibility.

RESULTS

 The facial phantom model received high scores in the LORI evaluation, with the highest ratings given to alignment with learning objectives and motivation. The model also scored well in terms of accessibility, content quality, and presentation design. However, feedback and adaptation received a lower score due to the static nature of the model.

CONCLUSION

 The facial phantom model shows promise as a valuable tool for teaching and developing competence in BoNT application for HS and blepharospasm. The model reduces the reliance on real patients for training, providing a broader and safer learning experience for neurology residents. It also provides a realistic learning experience and offers portability, cost-effectiveness, and ease of manufacturing for use in various medical training scenarios. It is an effective and accessible tool for teaching BoNT application.

Preemptive strategies and lessons learned from complications encountered with microvascular decompression for hemifacial spasm

OBJECTIVE

Microvascular decompression (MVD) is the only curative treatment modality for hemifacial spasm (HFS). Although generally considered to be safe, this surgical procedure is surrounded by many risks and possible complications. The authors present the spectrum of complications that they met in their case series, the possible causes, and the strategies recommended to minimize them.

METHODS

The authors reviewed a prospectively maintained database for MVDs performed from 2005 until 2021 and extracted relevant data including patient demographics, offending vessel(s), operative technique, outcome, and different complications. Descriptive statistics with uni- and multivariable analyses for the factors that may influence the seventh, eighth, and lower cranial nerves were performed.

RESULTS

Data from 420 patients were obtained. Three hundred seventeen of 344 patients (92.2%) with a minimum follow-up of 12 months had a favorable outcome. The mean follow-up (standard deviation) was 51.3 ± 38.7 months. Immediate complications reached 18.8% (79/420). Complications persisted in only 7.14% of patients (30/420) including persistent hearing deficits (5.95%) and residual facial palsy (0.95%). Temporary complications included CSF leakage (3.10%), lower cranial nerve deficits (3.57%), meningitis (0.71%), and brainstem ischemia (0.24%). One patient died because of herpes encephalitis. Statistical analyses showed that the immediate postoperative disappearance of spasms and male gender are correlated with postoperative facial palsy, whereas combined vessel compressions involving the vertebral artery (VA) and anterior inferior cerebellar artery can predict postoperative hearing deterioration. VA compressions could predict postoperative lower cranial nerve deficits.

CONCLUSIONS

MVD is safe and effective for treating HFS with a low rate of permanent morbidity. Proper patient positioning, sharp arachnoid dissection, and endoscopic visualization under facial and auditory neurophysiological monitoring are the key points to minimize the rate of complications in MVD for HFS.

Influence of unilateral eyelid spasms and botulinum toxin treatment on intraocular pressure measured by transpalpebral tonometer

PURPOSE

Eyelid spasms might be associated with elevated intraocular pressure (IOP) in hemifacial spasm (HFS) patients. IOP assessment using a Goldmann applanation tonometer (GAT) is often compromised by eyelid spasms. This study aimed to assess the effect of HFS on IOP measurements using the transpalpebral tonometer Diaton® before and after treatment with botulinum toxin type A (BTX-A) and compared Diaton® and GAT measurements after treatment with BTX-A.

METHODS

IOP measurements were obtained with Diaton® in 27 patients with moderate-to-severe HFS before and after treatment with BTX-A. After treatment, the IOP was also measured using GAT and the results were compared with the ones measured with a Diaton®. The patients underwent automated perimetry, OCT, and pachymetry for screening to glaucoma.

RESULTS

Mean IOP with Diaton® was 11 ± 3.42 mmHg before treatment in the affected eye and 9 ± 2.98 mmHg in the contralateral eye. This difference was statistically significant (P = 0.012). However, after treatment with BTX-A, no interocular difference was found in IOP obtained with Diaton® (P = 0.204) or GAT (P = 0.971). Comparison between GAT and Diaton® measurements showed no significant differences after BTX-A treatment between the affected (P = 0.212) and contralateral eye (P = 0.971).

CONCLUSIONS

A significant reduction in IOP measurements on the affected side of HFS patients was observed after treatment with BTX-A, demonstrating that eyelid spasms may increase the IOP. No significant difference was observed between Diaton® and GAT measurements after the application of BTX-A. No differences were found in automated perimetry, OCT, and CCT when comparing affected eyes with contralateral eyes.

Orbicularis Oculi Muscle Immunohistochemical, Metabolic, and Morphometric Differences in Affected and Nonaffected Sides in Hemifacial Spasm vs Healthy Subjects

BACKGROUND

Subtle morphological alterations have been reported even in the nonaffected side of the orbicularis oculi muscle in patients with hemifacial spasm. However, no previous study assessed immunohistochemical, metabolic, and morphometric alterations in orbicularis oculi muscle fibers in affected and nonaffected sides in patients with this condition, compared with samples obtained from healthy subjects. The purpose of this study is to objectively assess and compare orbicularis oculi muscle (OOM) samples of hemifacial spasm affected and nonaffected sides and healthy subjects.

METHODS

Orbicularis oculi samples from 8 patients with hemifacial spasm who had not been previously treated and 6 healthy subjects were prepared using hematoxylin and eosin, nicotinamide adenine dinucleotide tetrazolium reductase, cytochrome oxidase, succinate dehydrogenase, Gomori staining, and monoclonal antibodies against myosin slow and myosin fast. A digital image analysis software was used for objective analysis.

RESULTS

OOM fiber area was significantly greater in both affected ( P = 0.0379) and nonaffected sides ( P = 0.0012) of HFS samples when compared with control subjects' fibers. A significantly greater number of oxidative fibers were observed in both affected and nonaffected sides of patients with HFS when compared with control subjects ( P < 0.001 for both). A significantly greater percentage of slow fibers was observed in the affected side of HFS patients ( P = 0.0012) compared with control subjects.

CONCLUSIONS

This study's findings suggest that repeated contractions might lead to OOM fiber hypertrophy, increased mitochondrial metabolism, and possible conversion of fast-twitch orbicularis oculi muscle fibers into slow-twitch fibers in patients with HFS. Alterations were observed in affected and nonaffected sides, confirming initial findings that the nonaffected side is not normal in this unique condition.

Vestibular paroxysmia caused by contralateral tortuous vertebral artery: A case report

RATIONALE

Vestibular paroxysmia (VP) is characterized by spontaneous, recurrent, short, paroxysmal attacks of vertigo with or without tinnitus.

PATIENT CONCERNS

We report a case of paroxysmal recurrent vertigo accompanying clicking tinnitus on the left side in a 61-year-old patient. He had undergone microvascular decompression to treat the left-side hemifacial spasm 6 years prior. The patient first developed vertigo attacks about 3 years after microvascular decompression, and the attacks increased in frequency over the last 4 months. Video-nystagmography revealed a background right-beating nystagmus which was reversed every 55 seconds, to left-beating nystagmus for 17 seconds.

DIAGNOSIS

Brain magnetic resonance imaging and angiography demonstrated a compression of the cisternal segment of the left vestibulocochlear nerve between the tortuous right vertebral artery and the posterior wall of the left porus acusticus internus.

INTERVENTIONS AND OUTCOMES

Under the diagnosis of VP, 300 mg oxcarbazepine was administered daily, which relieved the symptoms dramatically.

LESSON

The neurovascular cross-compression of the vestibulocochlear nerve by the contralateral vertebral artery tortuosity can cause VP. Periodic paroxysms of right-beating nystagmus accompanying the left-side tinnitus during vertigo attacks in our patient can be explained by secondary central hyperactivity in both vestibular and cochlear nuclei following long-standing neurovascular cross-compression.

A novel task-specific dystonia type: Hemifacial spasm in a photographer

A 67-year-old male photographer who used traditional cameras that necessitated monocular focusing developed intermittent blepharospasms, evident only during and shortly after the voluntary contraction of the left eyelids while using the camera, a form of a task-specific blepharospasm. The spasms gradually progressed to involve the entire hemiface resulting in a task-specific hemifacial spasm that eventually evolved into a persistent hemifacial spasm. Our case report highlights the fact that focal dystonia may also develop in the facial muscles following chronic and repetitive muscle contractions, such as those performed by an older photographer who used traditional cameras that necessitated monocular focusing. To our knowledge, hemifacial spasm has not yet been recognized as a form of focal, task-specific dystonia. Moreover, occupational, focal dystonia has not been described in photographers.

Hemifacial spasm and other craniofacial movement disorders

Craniofacial dyskinesias encompass a variety of abnormal spontaneous craniofacial movements that often appear similar in morphology but are, in fact, of varied cause and nature. Although hemifacial spasm and blepharospasm are the two most common abnormal craniofacial movements, the clinician should be cognizant of other dyskinesias, particularly craniofacial dystonias, tremor, tic, chorea, and stereotypies. Most craniofacial dyskinesias respond favorably to injections of botulinum toxin type A or oral medications. Surgical treatment may be beneficial for refractory cases.

Hemifacial spasm

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