Muscle afferent block by intramuscular injection of lidocaine for the treatment of writer's cramp

[Therapeutic strategies for oromandibular dystonia]

Oromandibular dystonia is characterized by tonic or clonic involuntary spasms of the masticatory, lingual and / or muscles in the stomatognathic system. It is often misdiagnosed as craniomandibular dysfunction or psychiatric disease. According to clinical features, the oromandibular dystonia is classified into 6 subtypes (jaw closing-, jaw opening-, tongue-, jaw deviation-, jaw protrusion-, and lip dystonia). There are several treatment methods like botulinum toxin injection, muscle afferent block (injection of lidocaine and alcohol into the masticatory or tongue muscles for blocking muscle afferents from muscle spindle), occlusal splint, and oral surgery (coronoidotomy). Most of patients can be treated successfully according to subtype by combination of these treatments. Special treatment recommendations for each subtype were described in this focus article. Accurate diagnosis and treatment of oral dystonia requires comprehensive knowledge and skills of both oral and maxillofacial surgery and neurology. Therefore, collaboration among these departments is very important.

Botulinum Neurotoxin Therapy for Lingual Dystonia Using an Individualized Injection Method Based on Clinical Features

Lingual dystonia is a debilitating type of oromandibular dystonia characterized by involuntary, often task-specific, contractions of the tongue muscle activated by speaking or eating. Botulinum neurotoxin (BoNT) has been used to treat lingual dystonia; however, it is known to cause serious complications, such as dysphasia and aspiration. The purpose of this study was to evaluate the efficacy and adverse effects of individualized BoNT therapy for lingual dystonia. One-hundred-and-seventy-two patients (102 females and 70 males, mean age: 46.2 years) with lingual dystonia were classified into four subtypes based on symptoms of involuntary tongue movements: protrusion (68.6%), retraction (16.9%), curling (7.6%), and laterotrusion (7.0%). Patients were treated with BoNT injection into the genioglossus and/or intrinsic muscles via individualized submandibular and/or intraoral routes. Results were compared before and after BoNT therapy. Botulinum neurotoxin was injected in 136 patients (mean: 4.8 injections). Clinical sub-scores (mastication, speech, pain, and discomfort) in a disease-specific rating scale were reduced significantly (p < 0.001) after administration. Comprehensive improvement after BoNT injection, assessed using the rating scale, was 77.6%. The curling type (81.9%) showed the greatest improvement, while the retraction type showed the least improvement (67.9%). Mild and transient dysphasia occurred in 12.5% of patients (3.7% of total injections) but disappeared spontaneously within several days to two weeks. No serious side effects were observed. With careful diagnosis of subtypes and a detailed understanding of lingual muscle anatomy, individualized BoNT injection into dystonic lingual muscles can be effective and safe.

Pathogenesis of dystonia: is it of cerebellar or basal ganglia origin?

Dystonia is a disorder of motor programmes controlling semiautomatic movements or postures, with clinical features such as sensory trick, which suggests sensorimotor mismatch as the basis. Dystonia was originally classified as a basal ganglia disease. It is now regarded as a 'network' disorder including the cerebellum, but the exact pathogenesis being unknown. Rare autopsy studies have found pathology both in the striatum and the cerebellum, and functional disorganisation was reported in the somatosensory cortex in patients. Recent animal studies showed physiologically tight disynaptic connections between the cerebellum and the striatum. We review clinical evidence in light of this new functional interaction between the cerebellum and basal ganglia, and put forward a hypothesis that dystonia is a basal ganglia disorder that can be induced by aberrant afferent inputs from the cerebellum.

Muscle Selection for Focal Limb Dystonia

Selection of muscles for botulinum toxin injection for limb dystonia is particularly challenging. Limb dystonias vary more widely in the pattern of dystonic movement and involved muscles than cervical dystonia or blepharospasm. The large variation in how healthy individuals perform skilled hand movements, the large number of muscles in the hand and forearm, and the presence of compensatory actions in patients with dystonia add to the complexity of choosing muscles for injection. In this article, we discuss approaches to selecting upper and lower extremity muscles for chemodenervation treatment of limb dystonia.

Sensory abnormalities in focal hand dystonia and non-invasive brain stimulation

It has been proposed that synchronous and convergent afferent input arising from repetitive motor tasks may play an important role in driving the maladaptive cortical plasticity seen in focal hand dystonia (FHD). This hypothesis receives support from several sources. First, it has been reported that in subjects with FHD, paired associative stimulation produces an abnormal increase in corticospinal excitability, which was not confined to stimulated muscles. These findings provide support for the role of excessive plasticity in FHD. Second, the genetic contribution to the dystonias is increasingly recognized indicating that repetitive, stereotyped afferent inputs may lead to late-onset dystonia, such as FHD, more rapidly in genetically susceptible individuals. It can be postulated, according to the two factor hypothesis that dystonia is triggered and maintained by the concurrence of environmental factors such as repetitive training and subtle abnormal mechanisms of plasticity within somatosensory loop. In the present review, we examine the contribution of sensory-motor integration in the pathophysiology of primary dystonia. In addition, we will discuss the role of non-invasive brain stimulation as therapeutic approach in FHD.

Sensory aspects of movement disorders

Movement disorders, which include disorders such as Parkinson's disease, dystonia, Tourette's syndrome, restless legs syndrome, and akathisia, have traditionally been considered to be disorders of impaired motor control resulting predominantly from dysfunction of the basal ganglia. This notion has been revised largely because of increasing recognition of associated behavioural, psychiatric, autonomic, and other non-motor symptoms. The sensory aspects of movement disorders include intrinsic sensory abnormalities and the effects of external sensory input on the underlying motor abnormality. The basal ganglia, cerebellum, thalamus, and their connections, coupled with altered sensory input, seem to play a key part in abnormal sensorimotor integration. However, more investigation into the phenomenology and physiological basis of sensory abnormalities, and about the role of the basal ganglia, cerebellum, and related structures in somatosensory processing, and its effect on motor control, is needed.

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.

Botulinum toxin for treatment of dystonia

Botulinum toxin (BT) is used in various medical specialties. However, dystonia is still one of the most important indications for BT therapy. BT drugs consist of botulinum neurotoxin, complexing proteins and excipients. Botox, Dysport and Xeomin are BT type A drugs and produce similar therapeutic and adverse effects (AE). Neurobloc/MyoBloc is based upon BT type B. Its use is limited by substantial systemic anticholinergic AE. The potency of BT drugs may be compared as follows: Botox:Xeomin:Dysport:Neuobloc/MyoBloc = 1:1:3:40. BT selectively blocks the cholinergic innervation of striate and smooth muscles and exocrine glands. It can produce obligate, local and systemic AE. However, its overall AE profile including long-term safety is excellent. BT can be blocked by antibodies. Risk factors include single doses, interinjection intervals and the immunological quality of the BT drug applied. Planning of BT therapy is based upon target muscle identification and estimation of their dystonic involvement. For planning of BT therapy and BT placement, electromyography and imaging techniques may be used additionally. So far, total Xeomin and Botox doses of up to 840 MU have been used without clinically detectable systemic AE. BT can be used to treat focal dystonias including cranial, pharyngolaryngeal, cervical and limb dystonias. In segmental and generalized dystonias, BT therapy has to be focussed on the most relevant target muscles. Combinations with all other treatment options including deep brain stimulation are possible. Recent safety data and availability of immunologically improved BT drugs are now allowing higher BT doses thus expanding the use of BT into more widespread dystonias.

Mechanism and treatment of dropped head syndrome associated with parkinsonism

Dropped head syndrome (DHS) associated with parkinsonism is not frequent, but it markedly reduces the activities of daily living and is refractory. To elucidate the mechanism and treatment of DHS associated with parkinsonism, we assessed 28 parkinsonian patients with DHS (2 men and 26 women) by examining their clinical features and cervical-muscle-needle and surface electromyographic (EMG) recordings. We also evaluated the effects of lidocaine, muscle afferent block (MAB; 1% lidocaine mixed with ethanol), and botulinum toxin injected into the bilateral sternocleidomastoid muscles (SCMs), which were considered to be the affected muscles. In some patients, DHS occurred after the initiation or loading of dopamine agonists (less common after pergolide than cabergoline and pramipexole). Improvement was noted after a reduction in the dopamine agonist dose in some patients, and loading of l-dopa in others. Needle EMG revealed no evidence for weakness of the dorsal neck muscles. Surface EMG showed a gradual increase in SCMs activity upon passive head lifting. Lidocaine injection into SCMs markedly improved DHS, but the effect was temporary. The effect of botulinum toxin and MAB was not satisfactory. Whereas DHS could have a heterogeneous etiology, dopamine receptor sensitivity may play a role in its pathogenesis. For the treatment of DHS in parkinsonian patients, an increase in the dosage of l-dopa and a decrease in that of the dopamine agonist should be considered. Lidocaine injection (lidocaine test) could be useful for determining the most affected muscle before using botulinum toxin or MAB. Further studies are needed to examine the outcome of such treatments that include GPi-DBS.

Treatment of dystonia

Dystonia, defined as a neurological syndrome characterised by involuntary, patterned, sustained, or repetitive muscle contractions of opposing muscles, causing twisting movements and abnormal postures, is one of the most disabling movement disorders. Although gene mutations and other causes are increasingly recognised, most patients have primary dystonia without a specific cause. Although pathogenesis-targeted treatment is still elusive, the currently available symptomatic treatment strategies are quite effective for some types of dystonia in relieving involuntary movements, correcting abnormal posture, preventing contractures, reducing pain, and improving function and quality of life. A small portion of patients have a known cause and respond to specific treatments, such as levodopa in dopa-responsive dystonia or drugs that prevent copper accumulation in Wilson's disease. Therapeutic options must be tailored to the needs of individual patients and include chemodenervation with botulinum toxin injections for patients with focal or segmental dystonia, and medical treatments or deep brain stimulation for patients with generalised dystonia.

Pharmakologische Aspekte therapeutischer Botulinum-Toxin-Präparationen

Therapeutic preparations of botulinum toxin (BT) consist of botulinum neurotoxin (BNT), complexing proteins, and excipients. Depending on the target tissue, BNT can block cholinergic neuromuscular innervation of intra- and extrafusal muscle fibres or cholinergic autonomic innervation of sweat, lacrimal, and salival glands and smooth muscles. Indirect CNS effects are numerous; direct ones have not been reported after intramuscular application. Botulinum toxin type A is distributed as Botox, Dysport, Xeomin, Hengli/CBTX-A, and Neuronox and BT type B as NeuroBloc/Myobloc. Differences in potency labelling of therapeutic BT preparations can be corrected by introduction of a conversion factor of 1:3 between Botox and Dysport, of 1:1 between Botox and Xeomin, and of 1:40 between Botox and NeuroBloc/Myobloc. Acute adverse effects of BT can be obligate, local or systemic. Adverse effect profiles of the different preparations are similar. However, BT type B frequently produces additional autonomic systemic adverse effects. Long-term application does not produce additional adverse effects. BNT can be partially or completely blocked by antibodies. Risk factors include the amount of BNT applied at each injection series, the interval between injection series, and the specific biological potency (SBP) of the BT preparation used. The SBP is 5 equivalent mouse units/ng BNT for NeuroBloc, 60 for Botox, 100 for Dysport, and 167 for Xeomin. Xeomin should therefore have a particularly low antigenicity. Clinical confirmation of this predicition, however, is lacking.

Botulinum toxin: mechanisms of action

This review describes therapeutically relevant mechanisms of action of botulinum toxin (BT). BT's molecular mode of action includes extracellular binding to glycoproteine structures on cholinergic nerve terminals and intracellular blockade of the acetylcholine secretion. BT affects the spinal stretch reflex by blockade of intrafusal muscle fibres with consecutive reduction of Ia/II afferent signals and muscle tone without affecting muscle strength (reflex inhibition). This mechanism allows for antidystonic effects not only caused by target muscle paresis. BT also blocks efferent autonomic fibres to smooth muscles and to exocrine glands. Direct central nervous system effects are not observed, since BT does not cross the blood-brain-barrier and since it is inactivated during its retrograde axonal transport. Indirect central nervous system effects include reflex inhibition, normalisation of reciprocal inhibition, intracortical inhibition and somatosensory evoked potentials. Reduction of formalin-induced pain suggests direct analgesic BT effects possibly mediated through blockade of substance P, glutamate and calcitonin gene related peptide.

Botulinum toxin: mechanisms of action

Botulinum toxin (BT) has been perceived as a lethal threat for many centuries. In the early 1980s, this perception completely changed when BT's therapeutic potential suddenly became apparent. We wish to give an overview over BT's mechanisms of action relevant for understanding its therapeutic use. BT's molecular mode of action includes extracellular binding to glycoprotein structures on cholinergic nerve terminals and intracellular blockade of the acetylcholine secretion. BT affects the spinal stretch reflex by blockade of intrafusal muscle fibres with consecutive reduction of Ia/II afferent signals and muscle tone without affecting muscle strength (reflex inhibition). This mechanism allows for antidystonic effects not only caused by target muscle paresis. BT also blocks efferent autonomic fibres to smooth muscles and to exocrine glands. Direct central nervous system effects are not observed, since BT does not cross the blood-brain barrier and since it is inactivated during its retrograde axonal transport. Indirect central nervous system effects include reflex inhibition, normalisation of reciprocal inhibition, intracortical inhibition and somatosensory evoked potentials. Reduction of formalin-induced pain suggests direct analgesic BT effects possibly mediated by blockade of substance P, glutamate and calcitonin gene-related peptide.

The Therapeutic Potential of Botulinum Toxin

BACKGROUND

Botulinum toxin type A (BTX-A; commercial preparation BOTOX) is most well known for its effect on muscle contraction because of the BTX binding to the presynaptic nerve terminal, inhibiting the release of acetylcholine (ACH). The therapeutic benefit of BTX-A, however, can also be isolated to pain relief alone, suggesting that BTX-A also works through additional modes of action.

OBJECTIVE

This article provides insight by an experienced physician into four different case reports. Each case demonstrates the therapeutic potential of BTX-A and the possibility of a different mechanism of action for BTX other than the inhibition of ACH release.

RESULTS

Four patients, each with different symptoms such as relapsing-remitting multiple sclerosis, postherpetic neuralgia, peripheral neuropathy, and severe tingling caused by herniation of cervical vertebrae at the level of C8, were treated with BOTOX, and their symptoms were alleviated.

CONCLUSIONS

The BTX-A mechanism providing pain relief is hypothesized to be something other than muscle relaxation by inhibiting the release of ACH at the neuromuscular juncture, such as inhibition of the release of substance P or the blocking of autonomic pathways, etc. This article is intended to continue to keep physicians using this substance for dermatologic indications aware of the potential unsuspected effects.

Botulinum toxin therapy for cervical dystonia

Botulinum toxin revolutionized the treatment of cervical dystonia. In contrast to systemically active medications, the effect of botulinum toxin results from selective administration to weaken muscles involved in the dystonic posturing of the head. This article reviews the pathophysiologic basis of symptoms in cervical dystonia and how botulinum toxin alleviates them. Other therapeutic options are reviewed for comparison. This article discusses strategies for maximizing the clinical benefit of botulinum toxin in this disorder and reviews muscle selection and identification with electromyography.

Treatment of migraine headache with botulinum toxin type A

Migraine is a common headache disorder with profound implications on patients' quality of life and the overall health care system. Traditional treatment options have been less than optimal and many migraine patients lack confidence in over-the-counter and prescribed medications. BTX-A has shown promise as an efficacious, well-tolerated, long-lasting preventive therapy. Completed placebo-controlled trials showed that BTX-A injections for migraine resulted in fewer headaches, reduced headache severity and duration, reduced migraine-associated symptoms, and reduced use of migraine medications. Because the administration of BTX-A is nonsystemic, reported adverse events have been rare and mild. Larger trials are currently underway to further evaluate BTX-A efficacy and to determine optimal dosing and injection sites. Based on the collective experience of clinicians in neurology, facial plastic surgery, and otolaryngology, as well as supporting evidence from completed and ongoing clinical trials and theorized mechanism of action, an effective BTX-A approach for treatment of migraine is emerging. With further refinement to its use as prophylactic therapy, BTX-A can potentially be a primary option for candidate migraine sufferers and prescribing clinicians.

Idiopathic foot dystonia treated with intramuscular phenol injection

We describe a patient who developed involuntary, painless, dystonic contraction of the left foot on walking. The patient had been treated with botulinum toxin A without benefit. Examination showed that walking brought on a spasmodic twisting of the left foot, with extension and eversion of the ankle. The patient underwent an intramuscular phenol injection, which abolished the foot dystonia. This case suggests that intramuscular phenol treatment may be an alternative for patients where botulinum toxin was unable to relieve the dystonias.

[Muscle afferent block in the treatment of oromandibular dystonia. Difference in effect between masticatory and lingual muscles]

Oromandibular dystonia is a neuromuscular disorder characterized by tonic or clonic involuntary spasms of the masticatory and lingual muscles. We treated 50 patients with this movement disorder by injection of lidocaine and alcohol into the masticatory or tongue muscles to block muscle afferents from muscle spindle. The patients were divided according to clinical features into four groups: jaw-closing, jaw-opening, jaw-deviation, and tongue dystonias. Objective evaluation of the symptoms before and after therapy was based on a clinical scaling protocol in terms of four parameters (mastication, speech, pain, and discomfort scales). Symptoms improved in all patients without major side effects. The overall objective improvement (60.2+/-29.5%) was significantly (P<0.005, ANOVA) lower in tongue dystonia (14.1%) than in jaw-closing dystonia (67.6%) and jaw-opening dystonia (68.3%). Although the response of the muscle afferent block to tongue dystonia was hardly satisfactory, this treatment is suggested to be effective for oromandibular dystonia.

Stuttering: a dynamic motor control disorder

The purpose of this review is to determine what neural mechanisms may be dysfunctional in stuttering. Three sources of evidence are reviewed. First, studies of dynamic inter-relationships among brain regions during normal speech and in persons who stutter (PWS) suggest that the timing of neural activity in different regions may be abnormal in PWS. Second, the brain lesions associated with acquired stuttering are reviewed. These indicate that in a high percentage of cases, the primary speech and language regions are not affected but lesions involve other structures, such as the basal ganglia, which may modulate the primary speech and language regions. Third, to characterize the motor control disorder in stuttering, similarities and differences from focal dystonias such as spasmodic dysphonia (SD) and Tourette's syndrome (TS) are reviewed. This review indicates that the central control abnormalities in stuttering are not due to disturbance in one particular brain region but rather a system dysfunction that interferes with rapid and dynamic speech processing for production.

EDUCATIONAL OBJECTIVES

The reader will be able to describe: (1) the similarities and differences between stuttering and other speech motor control disorders, (2) which brain lesions are most likely to produce acquired stuttering in adults, and (3) what type of brain abnormality most likely underlies stuttering.

Factors influencing the therapeutic effect of muscle afferent block for oromandibular dystonia and dyskinesia: implications for their distinct pathophysiology

Oromandibular dystonia (OMD) is a focal dystonia manifested by involuntary masticatory and/or lingual muscle contractions. Muscle afferent block (MAB) by injecting anaesthetic and alcohol intramuscularly is recently used for the treatment of OMD. To study the factors affecting the efficacy of MAB, 44 patients with OMD were treated by local injection of lidocaine and ethanol. They were divided into four groups (spastic, rhythmic, dyskinetic, and task-specific) according to the pattern of incisal movement and involuntary contraction. We used a clinical scaling protocol in terms of four parameters (mastication, speech, pain, and discomfort) to evaluate the change of symptoms objectively. The relationship of improvement in clinical scores with various parameters was assessed statistically. The overall objective improvement was 60.2 +/- 29.5%. The scores decreased significantly (P<0.0001, paired t-test) after MAB. The maximal incisal velocity significantly correlated inversely with the clinical improvement, and MAB was particularly effective for spastic contraction. Dyskinetic and rhythmic groups showed variable and significantly less improvements than the spastic group. MAB is highly effective for OMD, but not for the patients with dyskinetic symptoms. The jaw movement pattern is an important factor for predicting the outcome. The difference in the response to MAB in OMD and oral and/or orofacial dyskinesia suggests the distinct pathophysiology between the two.

Botulinum toxin type A (BOTOX) for treatment of migraine

An open-label study and 2 double-blind, placebo-controlled studies have provided supporting evidence of botulinum toxin type A (BTX-A) as an effective, well-tolerated treatment for migraine. Observed durations of benefit were consistent with known properties of BTX-A. Findings suggest that response may vary by features of preinjection headaches, such as migraine frequency. The precise mechanism by which BTX-A provides pain relief is hypothesized to be related not only to acetylcholine inhibition but also to a blocking action on the parasympathetic nervous system. Additional studies that control factors likely to be related to response may lead to better understanding of the BTX-A effect on migraine and an optimal treatment protocol.

Abnormal cortical mechanisms of voluntary muscle relaxation in patients with writer's cramp: an fMRI study

Although it is hypothesized that there is abnormal motor inhibition in patients with dystonia, the question remains as to whether the mechanism related to motor inhibition is specifically impaired. The objective of the present study was to clarify the possible abnormalities of the mechanisms underlying voluntary muscle relaxation during motor preparation and execution in patients with writer's cramp, using event-related functional MRI. Eight patients with writer's cramp and 12 age-matched control subjects participated in the study. Two motor tasks were employed as an experimental paradigm. In the relaxation task, subjects were asked to hold their right wrist in the horizontal plane by maintaining moderate contraction of wrist extensor muscles in the premotor phase; they relaxed those muscles voluntarily just once during each fMRI scanning session. In the contraction task, subjects extended the right wrist voluntarily from the same premotor state as for the relaxation task. Five axial images covering the primary sensorimotor cortex (SMC) and supplementary motor area (SMA) were obtained once every second. Activated volumes in the left SMC and the SMA were significantly reduced in patients for both muscle relaxation and contraction tasks. These data suggest that there is impaired activation in both SMC and SMA in voluntary muscle relaxation and contraction in patients with writer's cramp. This implies that abnormalities of both inhibitory and excitatory mechanisms in motor cortices might play a role in the pathophysiology of focal dystonia.

Hand orthosis as a writing aid in writer's cramp

Writer's cramp is a focal, task-specific dystonia of the hand and wrist. It primarily affects people who do a significant amount of writing, and causes difficulties in writing. We present five cases with writer's cramp who showed improvement in their writing ability with an applied hand orthosis.

Botulinum toxin type A (BOTOX) for treatment of migraine

An open-label study and 2 double-blind, placebo-controlled studies have provided supporting evidence of botulinum toxin type A (BTX-A) as an effective, well-tolerated treatment for migraine. Observed durations of benefit were consistent with known properties of BTX-A. Findings suggest that response may vary by features of preinjection headaches, such as migraine frequency. The precise mechanism by which BTX-A provides pain relief is hypothesized to be related not only to acetylcholine inhibition but also to a blocking action on the parasympathetic nervous system. Additional studies that control factors likely to be related to response may lead to better understanding of the BTX-A effect on migraine and an optimal treatment protocol.

Customized EMG needle insertion guide for the muscle afferent block of jaw-deviation and jaw-opening dystonias

OBJECTIVE

Jaw-opening and jaw-deviation dystonias are characterized by mouth opening or lateral shift of the mandible due to involuntary contraction of the lateral pterygoid muscle, causing difficulties in speech or mastication. We introduce the method of muscle afferent block by using a removable device for inserting a hollow electromyographic needle.

STUDY DESIGN

A technique for fabricating a customized needle insertion guide into the lateral pterygoid muscle is described. Using the device, intramuscular injection of lidocaine and ethanol was performed in 3 patients with jaw-opening dystonia and 2 with jaw-deviation dystonia. Subjective improvement was assessed on a linear self-rating scale ranging from 0 (no improvement) to 100 points (complete cure).

RESULTS

The overall subjective improvement was 72% +/- 16.4% without major side effects.

CONCLUSIONS

The device is very useful for safe and accurate injection into the lateral pterygoid muscle. The muscle afferent block is effective for jaw-opening and jaw-deviation dystonias.

Botulinum toxin restores presynaptic inhibition of group Ia afferents in patients with essential tremor

We studied the effect of botulinum toxin A injection on the abnormal presynaptic phase of reciprocal inhibition between forearm antagonist muscles in patients with essential tremor. Ten patients with essential tremor were investigated before and 1 month after botulinum injection. Reciprocal inhibition was studied by conditioning the H reflex in forearm flexors with a radial-nerve stimulus delivered at a range of time intervals. Botulinum toxin produced a significant functional improvement in tremor (about 20%). Before botulinum toxin injection, patients had a reduced presynaptic phase of reciprocal inhibition. After botulinum toxin this phase was significantly more pronounced. The normal early disynaptic phase of reciprocal inhibition was normal before and after botulinum treatment. Although botulinum treatment reduced the size of the H reflex and the M wave to a similar extent, it left the H/M ratio unchanged. These findings show that botulinum toxin treatment restores presynaptic inhibition between forearm antagonist muscles. The results are also consistent with botulinum toxin having a beneficial effect in patients with essential tremor. Both effects probably depend upon the toxin's concurrent action on the extrafusal and intrafusal motor end-plates, the latter resulting in decreased spindle afferent input to the spinal cord.

Muscle afferent block for the treatment of oromandibular dystonia

Oromandibular dystonia is a focal dystonia involving the masticatory and tongue muscles, causing difficulties in speech or mastication. We treated 13 patients with this condition by injecting diluted lidocaine and alcohol intramuscularly. This method is aimed at reducing muscle spindle afferent activity. The symptoms had been resistant to other therapies such as pharmacotherapy or dental treatment. All patients showed clinical improvement after this therapy with reduced EMG activities in the affected muscles, whereas control injection of normal saline gave no changes in EMG activities. The overall subjective improvement was 57.7 +/- 25.1% (mean +/- standard deviation) in a self-rating scale. The mean response of the jaw elevator muscles (70 +/- 13.1%) was significantly higher (p < 0.02, t test) than that of the depressor muscles (38 +/- 28.4%). Despite the precise mechanism being unknown, this difference might be related to the smaller number of muscle spindles in the depressor than the elevator muscles. This therapy is useful for the treatment of drug-resistant oromandibular dystonia.

Extrafusal and intrafusal muscle effects in experimental botulinum toxin-A injection

The effects of botulinum toxin-A was compared on both extrafusal and intrafusal muscle fibers in the biceps femoris of Wistar rats. Four days after injection no action potentials were elicited with stimulation single-fiber electromyography on the injected side. Fourteen days after injection, jitter became measurable and these values were increased on the injected side. Extrafusal muscle fibers began to atrophy on the 4th day and this continued to the 14th day postinjection. Atrophy was also evident and progressive in intrafusal muscle fibers. Increased terminal innervation ratios, end-plate spread of cholinesterase, and increased density of very small myelinated fibers in large intramuscular nerves were observed 14 days postinjection. Both extrafusal and intrafusal fibers are cholinergically innervated, and both were progressively affected by botulinum toxin, perhaps varying in degree only. In addition to partial denervation, Botulinum toxin effects in dystonia may also be related to modified spindle afferent discharge.