Treatment of childhood myoclonus with botulinum toxin type A

Exploring the role of botulinum toxin in critical care

INTRODUCTION

Botulinum neurotoxin (BoNT) is one of the most potent and extensively studied neurotoxins with clinical applications across several different medical specialties. This review article explores the latest evidence for therapeutic applications of BoNT in patients receiving critical management in an intensive care unit (ICU).

AREAS COVERED

The authors did a literature search in PubMed, Google Scholar, and Texas Medical Center Library database for studies describing the use of BoNT in a critical care setting. They extracted information on study design, patient selection, methodology, and results of relevant studies. Based on initial identification of 85 studies and after conducting screening, the authors identified 61 studies to be included in this review. In an ICU setting, BoNT has been used for several neurological and non-neurological indications. However, the supporting evidence is mostly limited to small observational studies.

EXPERT OPINION

The use of BoNT in this setting is largely underutilized due to paucity of well-designed clinical trials and financial barriers. Further research is needed to provide evidence for the safety and efficacy of BoNT and to optimize the dosing and injection techniques for various conditions encountered in this setting.

Botulinum Toxin in Movement Disorders: An Update

Since its initial approval in 1989 by the US Food and Drug Administration for the treatment of blepharospasm and other facial spasms, botulinum toxin (BoNT) has evolved into a therapeutic modality for a variety of neurological and non-neurological disorders. With respect to neurologic movement disorders, BoNT has been reported to be effective for the treatment of dystonia, bruxism, tremors, tics, myoclonus, restless legs syndrome, tardive dyskinesia, and a variety of symptoms associated with Parkinson's disease. More recently, research with BoNT has expanded beyond its use as a powerful muscle relaxant and a peripherally active drug to its potential central nervous system applications in the treatment of neurodegenerative disorders. Although BoNT is the most potent biologic toxin, when it is administered by knowledgeable and experienced clinicians, it is one of the safest therapeutic agents in clinical use. The primary aim of this article is to provide an update on recent advances in BoNT research with a focus on novel applications in the treatment of movement disorders. This comprehensive review of the literature provides a critical review of evidence-based clinical trials and highlights recent innovative pilot studies.

Myoclonus

PURPOSE OF REVIEW

Myoclonus remains a challenging movement phenotype to characterize, evaluate, and treat. A systematic assessment of the temporal sequence, phenomenology, and distribution of movements can assist in the rational approach to diagnosis and management.

RECENT FINDINGS

Cortical forms of myoclonus are increasingly recognized as primarily cerebellar disorders. A syndrome of orthostatic myoclonus has been recognized by electrophysiology in patients with neurodegenerative disorders, mainly in Alzheimer disease, accounting for impairments in gait and balance previously mischaracterized as normal pressure hydrocephalus or orthostatic tremor. Tyrosine hydroxylase deficiency and Silver-Russell syndrome (uniparental disomy of chromosome 7) have been established as two novel causes of the myoclonus-dystonia syndrome. Mutations in the glycine receptor (GlyR) α1-subunit gene (GLRA1) explain the major expression of hyperekplexia, an inherited excessive startle disorder, butnewly identified mutations in GlyR β-subunit (GLRB) and glycine transporter 2 (GlyT2) genes (SLC6A5) account for "minor" forms of this disorder manifested as excessive startle and hypnic jerks. The entity previously known as palatal myoclonus has been reclassified as palatal tremor in recognition of its clinical and electromyographic features and no longer enters the differential diagnosis of myoclonic disorders. Increasing documentation of psychogenic features in patients previously characterized as having propriospinal myoclonus has cast doubts on the existence of this distinctive disorder.

SUMMARY

Myoclonus can be a prominent manifestation of a wide range of disorders. Electrophysiologic testing aids in distinguishing myoclonus from other mimics and classifying them according to cortical, subcortical, or spinal origin, which assists the choice of treatment. Despite the lack of randomized clinical trials, levetiracetam appears most effective in patients with cortical myoclonus, whereas clonazepam remains the only first-line therapeutic option in subcortical and spinal myoclonus.

The Use of Botulinum Toxin for the Treatment of Generalized Myoclonus in a DogS

A 13 mo old spayed female mixed-breed dog presented in a nonambulatory state that was attributed to severe myoclonus secondary to distemper. The authors hypothesized that mitigating the myoclonus would help the dog become ambulatory and expedite convalescence. They injected the severely affected muscles with botulinum toxin on two separate occasions over a period of 18 days. Those injections reduced the myoclonus, helping the dog become ambulatory and attaining a comfortable, functional state.

Botulinum toxin injections for simple partial motor seizures associated with pain

Intractable epilepsy with painful partial motor seizures is a relatively rare and difficult disorder to treat. We evaluated the usefulness of botulinum toxin to reduce ictal pain. Two patients received two or four botulinum toxin (BTX) injections at one-to-two-month intervals. Patient 1 had painful seizures of the right arm and hand. Patient 2 had painful seizures involving the left foot and leg. Injections were discontinued after improved seizure control following resective surgery. Both patients received significant pain relief from the injections with analgesia lasting at least two months. Seizure severity was reduced, but seizure frequency and duration were unaffected. For these patients, BTX was effective in temporarily relieving pain associated with muscle contraction in simple partial motor seizures. Our findings do not support the hypothesis that modulation of motor end-organ feedback affects focal seizure generation. BTX is a safe and reversible treatment that should be considered as part of adjunctive therapy after failure to achieve control of painful partial motor seizures.

The use of botulinum toxin A in children with cerebral palsy, with a focus on the lower limb

PURPOSE

The purpose of this review is to clarify the role of botulinum toxin serotype A (BTX-A) in the treatment of children with cerebral palsy (CP), with a special focus on the lower limb.

BACKGROUND

The treatment of spasticity is central in the clinical management of children with CP. BTX-A blocks the release of acetylcholine at the motor end plate, causing a temporary muscular denervation and, in an indirect way, a reduced spasticity. Children with increased tone develop secondary problems over time, such as muscle contractures and bony deformities, which impair their function and which need orthopaedic surgery. However in these younger children, delaying surgery is crucial because the results of early surgical interventions are less predictable and have a higher risk of failure and relapse. As BTX-A treatment reduces tone in a selective way, it allows a better motor control and muscle balance across joints, resulting in an improved range of motion and potential to strengthen antagonist muscles, when started at a young age. The effects are even more obvious when the correct BTX-A application is combined with other conservative therapies, such as physiotherapy, orthotic management and casts. There is now clear evidence that the consequences of persistent increased muscle tone can be limited by applying an integrated multi-level BTX-A treatment approach. Nevertheless, important challenges such as patient selection, defining appropriate individual goals, timing, dosing and dilution, accuracy of injection technique and how to measure outcomes will be questioned. Therefore, "reflection is more important than injection" remains an actual statement.

Pain characteristics and their association with quality of life and self-concept in children with hemiplegic cerebral palsy identified from a population register

OBJECTIVES

To describe and characterize the prevalence and quality of pain in a population-based community sample of children with hemiplegic cerebral palsy.

METHODS

Outcomes were assessed from 2 domains of the World Health Organization International Classification of Functioning, Disability and Health: body structure/function (upper limb spans, modified Ashworth scale, Tardieu scale, sensory function), activities-participation (Assessment of Motor and Process Skills), Pediatric Quality of Life Inventory (PedsQL), and self-perception (Harter Self-Perception Profile).

RESULTS

There were 107 participants of age (mean, 95% confidence interval) 8.94 years (8.23 to 9.65); 61 (57%) were boys and 58 (54%) had hemiplegia affecting the right side. Fifty-one (48%) reported pain. Pain mostly affected the involved side (n=28, 55%) and lower limb (n=19, 37%). Eighteen (35%) reported moderate to severe pain. Thirty-five (69%) said pain impacted on movement/activity and was of an aching quality (n=29, 57%). Mean (95% confidence interval) quality of life according to Pediatric Quality of Life Inventory was significantly lower for children experiencing pain compared with children experiencing no pain [parent 50.2 (45.9 to 54.5) vs. 60.1 (55.1 to 65.1), P<0.01; child 60.5 (55.4 to 65.6) vs. 75.8 (68.4 to 83.2), P<0.01]. The self-perception domains of Scholastic Competence [no pain, 3.02 (2.78 to 3.26); pain, 2.55 (2.31 to 2.79) P<0.01] and Behavioral Competence [no pain, 3.33 (3.07 to 3.60); pain, 2.88 (2.70 to 3.06) P<0.01] were significantly lower in children with pain aged > or =8 years.

DISCUSSION

Pain is common in children with hemiplegic cerebral palsy with qualities suggesting a nociceptive origin. Pain is associated with lower quality of life and self-perception. Results suggest clinicians should assess and actively manage pain in this population.

Botulinumtoxin A bei der Behandlung der infantilen Zerebralparese

Botulinum toxin A represents a significant development in the management of children and adolescents with spastic cerebral palsy. Prerequisites for an adequate result are a correct indication, an exact injection technique and an intensive post-treatment programme. Spastic muscle overactivity and the constant tendency of the involved muscles to shorten with growth cannot be treated by only one method. Therefore a multilevel approach and an integrated treatment schedule including plaster of Paris, orthoses and physiotherapy are currently the best ways to modify the disease process. The inclusion of objective clinical documentation techniques combined with 3-D instrumented gait analysis allows the determination of the indications more exactly and for monitoring the post-treatment results. If started early and correctly, this integrated management approach has the potential to modify the natural history of the disorder, and to reduce the frequency of later surgery.

Mouvements anormaux de l’enfant : nouveautés thérapeutiques

Abnormal movements are not uncommon in childhood. Due to the severity of the abnormal movements or to the functional disability, a medical treatment is often required; the wide range of available pharmacological molecules and the absence of therapeutic consensus highlight the limited efficacy of the medical treatment on dystonic or athetoid movements, or severe tic disorders. The recent identification of the enzymatic defect implicated in metabolic diseases led to the development of specific treatment for newly recognized disorders, with more or less interesting results (creatine ou biotine supplementation). Recent progress in functional neurosurgery opened new fields in the treatment of movement disorders. Intrathecal baclofen was proved effective in the treatment of secondary dystonia, especially in patients with cerebral palsy. Deep brain stimulation is now an established therapy for patients with a generalized dystonic syndrome. Given the successful results of pallidal stimulation in dystonia, the indication of this procedure has been discussed in other types of abnormal movements.

Myoclonus in childhood

The term "myoclonus" sounds esoteric, yet it is part of our normal physiology, occurring as a muscle jerk on drowsiness or falling asleep, during rapid eye movement (REM) sleep, and as hiccoughs. Myoclonus is also a developmental feature of the human nervous system, comprising some of the earliest fetal movements. In pathologic settings, myoclonus may be the only neurologic abnormality, as in essential myoclonus, but more often it is one symptom of a larger neurologic problem. The vast etiologic spectrum of symptomatic myoclonus can be bewildering, but defining the underlying problem may provide the opportunity to develop specific therapies. Otherwise, treatment is merely symptomatic. The approach to the patient should be to verify the nature of the movement disorder and establish a specific etiologic diagnosis. A battery of neurophysiologic, neuroradiologic, and other laboratory studies is needed to localize the origin of the myoclonus and identify causative lesions. Drug treatment is largely empiric but must be systematic and aimed at restoring activities of everyday living. Unlike in epilepsies, in myoclonus multiple drugs usually must be combined to attain functional improvement.

Pharmacotherapy with botulinum toxin: harnessing nature's most potent neurotoxin

Botulinum toxin (BTX), a potent biologic neurotoxin, commonly is associated with lethal outbreaks of food poisoning; however, it also plays a role as a therapeutic agent. Since the 1970s physicians have investigated BTX therapy in patients with neurologic disorders. The number of applications greatly expanded over the years to include certain focal dystonias (blepharospasm, torticollis, laryngeal dystonias, writer's cramp), strabismus, and a wide variety of other indications (gastrointestinal disorders, cosmetic wrinkle correction, spasticity, hyperhidrosis). BTX's safety and efficacy are reviewed.