Effects of local injections of botulinum toxin on electrophysiological parameters in patients with hemifacial spasm: role of synaptic activity and size of motor units

How does botulinum toxin really work?

Over the past 30 years, Botulinum toxin (BoNT) has emerged as an effective and safe therapeutic tool for a number of neurological conditions, including dystonia. To date, the exact mechanism of action of BoNT in dystonia is not fully understood. Although it is well known that BoNT mainly acts on the neuromuscular junction, a growing body of evidence suggests that the therapeutic effect of BoNT in dystonia may also depend on its ability to modulate peripheral sensory feedback from muscle spindles. Animal models also suggest a retrograde and anterograde BoNT transportation from the site of injection to central nervous system structures. In humans, however, BoNT central effects seem to depend on the modulation of afferent input rather than on BoNT transportation. In this chapter, we aimed to report and discuss research evidence providing information on the possible mechanisms of action of BoNT in relation to treatment of dystonia.

Motor unit distribution and recruitment in spastic and non-spastic bilateral biceps brachii muscles of chronic stroke survivors

Objective.This study aims to characterize the motor units (MUs) distribution and recruitment pattern in the spastic and non-spastic bilateral biceps brachii muscles (BBMs) of chronic stroke survivors.Approach.High-density surface electromyography (HD-sEMG) signals were collected from both spastic and non-spastic BBMs of fourteen chronic stroke subjects during isometric elbow flexion at 10%, 30%, 50% and 100% maximal voluntary contractions (MVCs). By combining HD-sEMG decomposition and bioelectrical source imaging, MU innervation zones (MUIZs) of the decomposed MUs were first localized in the 3D space of spastic and non-spastic BBMs. The MU depth defined as the distance between the localized MUIZ and its normal projection on the skin surface was then normalized to the arm radius of each subject and averaged at given contraction level. The averaged MU depth at different contraction levels on a specific arm side (intra-side) and the bilateral depths under a specific contraction level (inter-side) were compared.Main results.The average depth of decomposed MUs increased with the contraction force and significant differences observed between 10% vs 50% (p< 0.0001), 10% vs 100% (p< 0.0001) and 30% vs 100% MVC (p= 0.0017) on the non-spastic side, indicating that larger MUs with higher recruitment threshold locate in deeper muscle regions. In contrast, no force-related difference in MU depth was observed on the spastic side, suggesting a disruption of orderly recruitment of MUs with increase of force level, or the MU denervation and the subsequent collateral reinnervation secondary to upper motor neuron lesions. Inter-side comparison demonstrated significant MU depth difference at 10% (p= 0.0048) and 100% force effort (p= 0.0026).Significance.This study represents the first effort to non-invasively characterize the MU distribution inside spastic and non-spastic bilateral BBM of chronic stroke patients by combining HD-sEMG recording, EMG signal decomposition and bioelectrical source imaging. The findings of this study advances our understanding regarding the neurophysiology of human muscles and the neuromuscular alterations following stroke. It may also offer important MU depth information for botulinum toxin injection in clinical post-stroke spasticity management.

Effect of the refrigerator storage time on the potency of botox for human extensor digitorum brevis muscle paralysis

Background and Purpose

It is recommended that Botox be used within 5 hours of reconstitution, which results in substantial quantities being discarded. This is not only uneconomic, but also inconvenient for treating patients. The aim of this study was to determine the potencies of Botox used within 2 hours of reconstitution with unpreserved saline, the same Botox refrigerated (at +4℃) 72 hours after reconstitution, and during the next 4 consecutive weeks (weeks 1, 2, 3, and 4). This comparison was used to determine the length of refrigeration time during which reconstituted Botox will maintain the same efficacy as freshly reconstituted toxin.

Methods

Individual paralysis rates in the extensor digitorum brevis (EDB) compound muscle action potential (CMAP) amplitude and area were measured 1 week after injecting fresh reconstituted 2.5 MU of Botox on one side of the foot, and when the same quantity of Botox that had been refrigerated for a designated time (i.e., 72 h, or 1, 2, 3, or 4 weeks) into the other side of the foot. The EDB CMAP amplitude and area at 12 and 16 weeks postinjection were also measured to compare the efficacy durations in all five comparative groups.

Results

Ninety-four volunteers were divided into five groups according to the refrigerator storage time of the second Botox injection. The paralysis of the EDBs was significant for each injection of Botox, both fresh and refrigerated, with no statistically significant differences between them, regardless of the refrigeration time. There was a tendency toward increased CMAP amplitude and area at 12 or 16 weeks postinjection (p<0.0001). The duration of effective muscle paralysis did not differ significantly throughout the 16-week follow-up period between all five groups.

Conclusions

The potency of reconstituted Botox is not degraded by subsequent refrigeration for 4 weeks. However, there are definite concerns regarding its sterility, and hence its safety, since multiple withdrawals from the same vial over long periods can introduce bacterial contamination.

Botulinum toxins: mechanisms of action, antinociception and clinical applications

Botulinum toxin (BoNT) is a potent neurotoxin that is produced by the gram-positive, spore-forming, anaerobic bacterium, Clostridum botulinum. There are 7 known immunologically distinct serotypes of BoNT: types A, B, C1, D, E, F, and G. Clostridum neurotoxins are produced as a single inactive polypeptide chain of 150kDa, which is cleaved by tissue proteinases into an active di-chain molecule: a heavy chain (H) of ∼100 kDa and a light chain (L) of ∼50 kDa held together by a single disulfide bond. Each serotype demonstrates its own varied mechanisms of action and duration of effect. The heavy chain of each BoNT serotype binds to its specific neuronal ecto-acceptor, whereby, membrane translocation and endocytosis by intracellular synaptic vesicles occurs. The light chain acts to cleave SNAP-25, which inhibits synaptic exocytosis, and therefore, disables neural transmission. The action of BoNT to block the release of acetylcholine botulinum toxin at the neuromuscular junction is best understood, however, most experts acknowledge that this effect alone appears inadequate to explain the entirety of the neurotoxin's apparent analgesic activity. Consequently, scientific and clinical evidence has emerged that suggests multiple antinociceptive mechanisms for botulinum toxins in a variety of painful disorders, including: chronic musculoskeletal, neurological, pelvic, perineal, osteoarticular, and some headache conditions.

Functional end-plate recovery in long-term botulinum toxin therapy of hemifacial spasm: a nerve conduction study

Botulinum toxin type-A is currently thought to be effective and safe for hemifacial spasm (HFS). The pre-synaptic block of acetylcholine release at the neuromuscular junction induces depression of orbicularis oculi muscle compound motor action potential (CMAP). The aim of our study was to evaluate at what extent end-plate functional recovery is possible even in botulinum toxin treatments lasting up to 15 years. We examined 81 outpatients with primary HFS (mean treatment duration = 7.2 ± 4.2 years) who underwent neurophysiologic study, once clinical effect of the previous treatment had vanished. The mean CMAP amplitude, mean rectified amplitude of response 1 (R1) of the blink reflex and area of response 2 (R2) of treated orbicularis oculi muscle were measured in comparison to the controlateral side. Mean amplitude of the above mentioned parameters was slightly lower (about 20%; p < 0.001) in the treated side at the end of the follow-up period (4.7 ± 1.7 months). The CMAP amplitude reduction weakly correlated with the interval from last treatment, while other neurophysiologic parameters did not change due to treatment duration or total toxin amount. Our study demonstrates that botulinum toxin affects compound motor action potential and blink-reflex responses for at least 4-5 months in HFS patients. The residual block is slight and does not increase with repeated injections after several years of treatment. Our study, beside confirming the long-term efficacy of botulinum toxin treatment for HFS, provides neurophysiologic evidence that therapeutic effect may be obtained without hindering the regenerative potential of the nerve-muscle complex.

Botulinum toxin-induced focal paresis in mice is unaffected by muscle activity

INTRODUCTION

To test the hypothesis that the efficacy of botulinum toxin depends on the activity of the neuromuscular junction, we developed an in vivo paradigm to determine the degree and duration of low-dose botulinum toxin-induced focal paresis in mice.

METHODS

We combined an automated wheel-running paradigm with low-dose botulinum toxin injections into the calf muscles of wild-type mice. Half of the mice were injected either before the nightly running or before the daily resting period.

RESULTS

After botulinum toxin injections, running distance and maximum velocity decreased dose-dependently. The degree and duration of decrease between the respective groups with regard to the time-points of injection were identical.

CONCLUSIONS

This in vivo paradigm quantifies the degree of otherwise clinically inapparent botulinum toxin-induced focal calf muscle paresis. Increased muscle activity after low-dose injections does not influence the efficacy of botulinum toxin in normal muscles.

Neurophysiological changes after intramuscular injection of botulinum toxin

Botulinum toxin (BT) acts peripherally by inhibiting acetylcholine release from the presynaptic neuromuscular terminals and by weakening muscle contraction. Therefore, its clinical benefit is primarily due to its peripheral action. As a result, local injection of BT has become a successful and safe tool in the treatment of several neurological and non-neurological disorders. Studies in animals have also shown that the toxin can be retrogradely transported and even transcytosed to neurons in the central nervous system (CNS). Further human studies have suggested that BT could alter the functional organisation of the CNS indirectly through peripheral mechanisms. BT can interfere with and modify spinal, brainstem and cortical circuits, including cortical excitability and plasticity/organisation by altering spindle afferent inflow directed to spinal motoneurons or to the various cortical areas. It is well demonstrated that the distant CNS effects of BT treatment parallel the peripheral effect, although there is limited evidence as to the cause of this. Therefore, further studies focussed on central changes after BT treatment is needed for a better understanding of these non-peripheral effects of BT.

Effect of botulinum neurotoxin treatment in the lateral spread monitoring of microvascular decompression for hemifacial spasm

INTRODUCTION

Botulinum neurotoxin (BtNtx) treatment for hemifacial spasm (HFS) prior to microvascular decompression (MVD) is hypothesized to be a factor in the variability of intraoperative neurophysiological monitoring (IONM) during this procedure.

METHODS

We analyzed 282 MVDs performed at the University of Pittsburgh Medical Center between January 1, 2000 and December 31, 2007. We retrospectively compared the lateral spread response (LSR) in the mentalis muscle when stimulus-triggered electromyography (EMG) was elicited from the facial nerve. Previous BtNtx treatment was the grouping factor.

RESULTS

Baseline LSR amplitudes during MVD (prior BtNtx: mean = 341.47 μV; no BtNtx: mean = 241.81 μV) were significantly different between groups (df = 1,281; t = -2.463; P = 0.014). Comparisons of latency and current threshold at baseline, as well as HFS disappearance or LSR persistence after the procedure, did not achieve statistical significance.

CONCLUSIONS

HFS patients treated with BtNtx prior to MVD demonstrated higher LSR baseline amplitudes during IONM. This could be related to muscle poly-reinnervation after recovery from repeated BtNtx use.

Neurophysiological effects of botulinum toxin type a

Botulinum toxin type A (BoNT-A) acts peripherally by inhibiting acetylcholine release from the presynaptic neuromuscular terminals, thus weakening muscle contraction, and its clinical benefit depends primarily on the toxin's peripheral action. In addition to acting directly at the neuromuscular junction, the toxin alters sensory inputs to the central nervous system, thus indirectly inducing secondary central changes. Some of the long-term clinical benefits of BoNT-A treatment may also reflect plastic changes in motor output after the reorganization of synaptic density.

Nerve stimulation boosts botulinum toxin action in spasticity

Spasticity leads to functional and structural changes in nerves and muscles, which alter skeletal muscle function. To evaluate whether short-term electrical nerve stimulation (NS) improves the effect of botulinum toxin in spastic skeletal muscle, we studied changes in the amplitude of the compound muscle action potential (CMAP) recorded from the extensor digitorum brevis (EDB) muscle in response to peroneal nerve stimulation at the ankle after injection of botulinum toxin type A (BTXA) alone or combined with short-term NS. In paraparetic patients, both EDB muscles were injected with BTXA; and NS was applied to one EDB muscle alone. All patients received a 30-minute session of electrical NS once a day for 5 consecutive days after BTXA injection. We used two different stimulation frequencies (low-frequency, 4 Hz; and high-frequency, 25 Hz). EDB-CMAP amplitudes were evaluated before BTXA injection (day 0) and changes in CMAP amplitude, expressed as a percentage (CMAP%), were measured at various time points over a 30-day period after BTXA injection. We compared changes in the CMAP% amplitude on the stimulated and contralateral nonstimulated sides. We also studied the electromyographic activity recorded from EDB muscles over a 30-day period. CMAP% amplitudes measured at all time points after BTXA injections were significantly reduced in both EDB muscles. On days 4, 10, and 15, the CMAP% amplitude reduction was significantly greater for the low-frequency stimulated EDB than for the contralateral nonstimulated EDB. No significant differences in CMAP% were observed for the high-frequency stimulated and nonstimulated EDB. After BTXA injection, spontaneous activity appeared in both EDB muscles; but it appeared earlier and involved larger areas in the stimulated than in the nonstimulated EDB. In conclusion, short-term NS accelerates the effectiveness of intramuscular BTXA injections on the neuromuscular blockade in patients with spastic paraparesis and could induce a rapid and persistent improvement in spasticity. Its action probably arises mainly from low-frequency NS.

Botulinum toxin type-A treatment in spastic paraparesis: a neurophysiological study

OBJECTIVE

The aim of this study was to verify the action of Botulinum toxin type-A (BoNT-A) by means of neurophysiological techniques, in patients presenting lower limb spasticity and requiring BoNT-A injections in the calf muscles, due to the poor response to medical antispastic treatment.

SUBJECTS AND METHOD

Patients presenting paraparesis were enrolled. They underwent clinical evaluation for spasticity according to the Ashworth scale and neurophysiological recordings including: motor evoked potentials (MEPs) to transcranial magnetic stimulation (TMS) of the leg area; compound motor action potential (cMAP) to tibial nerve stimulation, F-wave, and H-reflex before the treatment and 24 h, 2 weeks and 1 month after the injection of BoNT-A. In all patients, gastrocnemius was treated and in some cases soleus or tibialis posterior muscles were also injected.

RESULTS

In all patients, BoNT-A injections induced a clear clinical improvement as showed by the reduced spasticity values of the Ashworth scale. A significant increment of MEP latency and central conduction time (CCT) duration were observed 2 weeks after the treatment only in the injected muscles.

CONCLUSIONS

Prolonged MEP latencies and CCT after BoNT-A injections is probably due to a central alteration in responsiveness of spinal motor neurons to descending impulses from the corticospinal tracts. Such changes represent objective parameters heralding clinical efficacy of treatment.

Management of spasticity associated pain with botulinum toxin A

Lesions of the central nervous system often result in an upper motor neuron syndrome including spasticity, paresis with pyramidal signs, and painful spasms. Pharmacological treatment with oral antispasticity drugs is frequently associated with systemic side effects which limit their clinical use. Botulinum Toxin A (BtxA) injected in spastic muscles has been shown to be effective in reducing muscle tone, but only few studies have reported pain relief as additional benefit. Therefore, we investigated the effects of local BtxA injections in 60 patients with acute (< 12 months) and chronic spasticity and pain in a prospective multicenter study. Target muscles for BtxA were selected on the basis of clinical examination. Intramuscular BtxA injections were placed in muscles exhibiting increased muscle tone in combination with pain during passive joint movement. Patients received a mean total dose of 165.7 +/- 108.2 [30-400] units BOTOX((R)) per treatment session in a mean 3.4 +/- 1.5 muscles. Baseline and follow-up (mean 5.9 weeks) measures included a patient self-assessment of pain and function on a five-level scale, a physician's evaluation of function, and a global rating of response to BtxA. Fifty-four of sixty patients experienced improvement in pain without subjective functional improvement. The effects were comparable in acute (n = 17) and chronic (n = 43) spasticity. Physician's assessment of gain in function increased significantly (p < 0.05) only in patients with chronic spasticity. No serious adverse event was observed. Mild reversible side effects (local pain, hematoma, edema, mild weakness) were observed in four patients. In conclusion, we found that intramuscular BtxA injections are a potent, well-tolerated treatment modality to significantly reduce spasticity-related local pain. This problem may be a main indication, especially in patients with poor response or intolerable side effects to oral medication.

Serial SFEMG studies of orbicularis oculi muscle after the first administration of botulinum toxin

Serial single fiber electromyography (SFEMG) examinations of orbicularis oculi muscle in patients with blepharospasm or hemifacial spasm treated with botulinum toxin injections were performed. The aim of the study was to evaluate the impairment of neuromuscular transmission, to follow reinnervation after botulinum toxin administration and to find out whether there was a relationship between SFEMG parameters and clinical symptoms. Examinations were performed before injection, during early and late remission of symptoms, and after recurrence of the involuntary movement. Severe impairment of neuromuscular transmission, as revealed by increased jitter and increased presence of abnormal potential pairs and pairs with blocking, was found in early remission, but fiber density remained unchanged when compared with pretreatment values. In late remission, increased fiber density was registered for the first time. The recurrence of involuntary movements was related to the further increase of fiber density and tendency to normalization of jitter parameters. The study therefore suggests that formation of new neuromuscular junctions and their functional maturation is responsible for muscle recovery after botulinum toxin administration.

Effect of muscle activity immediately after botulinum toxin injection for writer's cramp

Animal and human studies have shown that nerve stimulation enhances some effects of botulinum toxin (btx A) injection. Voluntary muscle activity might work similarly and would focus the effect of an injection into the active muscles. We studied the effects of exercise immediately after btx A injection in eight patients with writer's cramp with established response to btx A over two injection cycles with a single-blinded, randomized, crossover design. Immediately after the first study injection, they were randomly assigned to write continuously for 30 min or have their hand and forearm immobilized for 30 min. Following the second injection, they were assigned the alternate condition. Patients were assessed just before each injection, and at 2 weeks, 6 weeks, and 3 months post-injection. Assessment included objective strength testing, self-reported rating of benefit and weakness, and blinded evaluation of videotapes and writing samples of the patients writing a standard passage. Strength testing showed that the maximum weakness occurred at 2 weeks post-injection, but the benefit was maximum at 6 weeks post-injection. The "write" condition resulted in greater reduction in strength than the "rest" condition. Btx A treatment led to improvement in self-reported ratings, writer's cramp rating scale scores by blinded raters, and reduction in writing time, but the differences between the "write" and "rest" conditions were not significant. We conclude that voluntary muscle activity immediately after btx A injection leads to greater reduction in muscle strength. Our findings raise the possibility that voluntary muscle activation may allow reduction of btx A doses and favorably alter the balance of benefit and side effects of btx A injections.

A re-evaluation of the mechanism of action of botulinum toxin on facial movement disorders in man

Despite a lot of research aimed at clarifying the mechanism of action of botulinum toxin, mostly at supraspinal levels, a complete understanding of it is still elusive. However, recent investigations, including our own, allow us to suggest that, in facial muscles, the effects of botulinum toxin are not only in the neuromuscular junctions affecting the acetylcholine release but also modify the sensory inflow with subsequent changes on the muscle spindle-gammamotoneuron system.

Hemifacial spasm due to posterior fossa tumors: the impact of tumor location on electrophysiological findings

Ephaptic transmission is one of the electrophysiological hallmarks of hemifacial spasm. It is generally accepted that in the majority of patients with idiopathic hemifacial spasm, microvascular compression of the facial nerve at the site where the nerve exits the brain stem is the underlying cause. Whether the actual site of the ephapse is at the site of the lesion or at a nuclear level due to hyperexcitability of the facial motor nucleus is still controversial. Rarely, hemifacial spasm may be due to space occupying lesions in the cerebellopontine angle or in the brain stem. We report the electrophysiological findings of four patients with hemifacial spasm due to extra-axial tumors in different locations of the posterior fossa. The location of the tumor was intrameatal in one patient, in the cerebellopontine angle in two patients and in the brain stem in another patient. Facial nerve motor neurographies including transcranial magnetic stimulation revealed abnormal findings in two patients. Selective stimulation of facial nerve branches demonstrated delayed (ephaptic) responses in all but one patient whose hemifacial spasm had disappeared after treatment with carbamazepine. The latencies of the delayed responses did not correlate with the tumor location. In sum, the site of ephaptic transmission cannot be reliably determined by latency measurements of the delayed response because of its variability which is probably caused by the different size and diameter of the axons participating in ephaptic transmission as well as by the extent of focal demyelination at the site of the lesion. A neuroradiological work up including MR imaging should be mandatory in all patients with hemifacial spasm because electrophysiological studies fail to differentiate between idiopathic and symptomatic hemifacial spasm.

[Botulinum toxin A: experience in the treatment of 115 patients]

Botulinum toxin A is the more efficient therapy of focal dystonias and hemifacial spasm. Our experience with botulinum toxin A injections in 115 patients is reported. Marked or total improvement was achieved in all 45 patients with hemifacial spasm, in 70% of 20 patients with essential blepharospasm and in 71.4% of 14 patients with Meige's syndrome. In 65.2% of 23 patients with cervical dystonia marked but no total improvement was obtained. The worse results were seen in the 6 patients with hand dystonia (writers cramp), in whom marked improvement was obtained in just two. Mild and transient complications occurred in up to 24.4%, eyelid ptosis and eyelid weakness being the most frequent. One patient with Meige's syndrome had an aspiration pneumonia following dysphagia. Our results are in agreement with others, showing that botulinun toxin A is a useful and safe treatment for these conditions.

The variability in the clinical effect induced by botulinum toxin type A: the role of muscle activity in humans

When botulinum toxin (BT) is administered for the first time at fixed doses, variable clinical responses can be observed in patients with the same form of dystonic disorder. Many factors may contribute to this phenomenon, including the variability rate of absorption of the drug. Animal experimental models (rat diaphragm preparation) have demonstrated an increased absorption of BT in the terminal nerve endings of the muscle under repetitive electrical stimulation, suggesting that "muscle activity" also may play an important role. The aim of our study was to evaluate in humans the role of the muscle activity on the variability of the effect induced by BT type A. Eleven patients with blepharospasm and idiopathic facial hemispasm were studied by using neurophysiologic techniques. In nine patients, both extensor digitorum brevis (EDB) muscles were injected with low (3 IU), fixed doses of type A BT. For the first 24 h after administration of the drug, periodic electrical stimulation of only one EDB was used. The subsequent percentage changes in compound muscle action potential (CMAP) amplitude was calculated at different intervals over a 30-day period. The percentage in the CMAP for the stimulated EDB was compared with that of the contralateral nonstimulated side. We found that the effect of the induced neuromuscular blockade was significantly greater for the stimulated side. In the other two patients, we injected BT in one EDB and the same volume of normal saline solution in the contralateral muscle to assess the stability of the CMAP in untreated muscle over time. We observed that the CMAP was unchanged in the untreated EDB; therefore we concluded that muscle activity plays an important role in the variability of clinical response often seen.