Subcutaneous Botulinum toxin type A reduces capsaicin-induced trigeminal pain and vasomotor reactions in human skin

Clinical Conditions Targeted by OnabotulinumtoxinA in Different Ways in Medicine

OnabotulinumtoxinA (BT-A) is used in different medical fields for its beneficial effects. BT-A, a toxin originally produced by the bacterium Clostridium botulinum, is widely known for its ability to temporarily paralyze muscles by blocking the release of acetylcholine, a neurotransmitter involved in muscle contraction. The literature continually reports new hypotheses regarding potential applications that do not consider blockade of acetylcholine release at the neuromuscular junction as a common pathway. In this opinion article, it is our aim to investigate the different pathway targets of BT-A in different medical applications. First of all, the acetylcholine effect of BT-A is used to reduce wrinkles for cosmetic purposes, in the treatment of urological problems, excessive sweating, temporomandibular joint disorders, obesity, migraine, spasticity in neurological diseases, and in various cases of muscle overactivity such as cervical dystonia, blepharospasm, and essential head tremor. In another potential pathway, glutamate A, CGRP, and substance P are targeted for pain inhibition with BT-A application in conditions such as migraine, trigeminal neuralgia, neuropathic pain, and myofascial pain syndrome. On the other hand, as a mechanism different from acetylcholine and pain mediators, BT-A is used in the treatment of hair loss by increasing oxygenation and targeting transforming growth factor-beta 1 cells. In addition, the effect of BT-A on the apoptosis of cancer cells is also known and is being developed. The benefits of BT-A applied in different doses to different regions for different medical purposes are shown in literature studies, and it is also emphasized in those studies that repeating the applications increases the benefits in the long term. The use of BT-A continues to expand as researchers discover new potential therapeutic uses for this versatile toxin.

Botulinum toxin type A is a potential therapeutic drug for chronic orofacial pain

BACKGROUND

Botulinum toxin type A (BTX-A), produced by the gram-positive anaerobic bacterium Clostridium botulinum, acts by cleaving synaptosome-associated protein-25 (SNAP-25), an essential component of the presynaptic neuronal membrane that is necessary for fusion with the membrane proteins of neurotransmitter-containing vesicles. Recent studies have highlighted the efficacy of BTX-A in treating chronic pain conditions, including lower back pain, chronic neck pain, neuropathic pain, and trigeminal neuralgia, particularly when patients are unresponsive to traditional painkillers. This review focuses on the analgesic effects of BTX-A in various chronic pain conditions, with a particular emphasis on the orofacial region.

HIGHLIGHT

This review focuses on the mechanisms by which BTX-A induces analgesia in patients with inflammatory and temporomandibular joint pain. This review also highlights the fact that BTX-A can effectively manage neuropathic pain and trigeminal neuralgia, which are difficult-to-treat chronic pain conditions. Herein, we present a comprehensive assessment of the central analgesic effects of BTX-A and a discussion of its various applications in clinical dental practice.

CONCLUSION

BTX-A is an approved treatment option for various chronic pain conditions. Although there is evidence of axonal transport of BTX-A from peripheral to central endings in motor neurons, the precise mechanism underlying its pain-modulating effects remains unclear. This review discusses the evidence supporting the effectiveness of BTX-A in controlling chronic pain conditions in the orofacial region. BTX-A is a promising therapeutic agent for treating pain conditions that do not respond to conventional analgesics.

Efficacy and Safety of Botulinum Toxin Type A in the Treatment of Trigeminal Neuralgia: An Update on Systematic Review With Meta-analyses

OBJECTIVE

Pain management in patients with TN is challenging, as facial pain often does not respond well to conventional therapies. Botulinum toxin type A (BTX-A) has been suggested as a potential treatment option, but there is limited evidence regarding its long-term efficacy. This review aimed to analyze the current data for the use of in the treatment of trigeminal neuralgia (TN) and highlight the evidence for its efficacy and safety.

METHODS

A comprehensive search was conducted in various databases (PubMed, Scopus, Embase, ClinicalTrials, and Cochrane Library) to identify clinical studies evaluating the use of BTX-A in TN until October 2023. Randomized controlled trials (RCTs), single-arm studies, and stratified studies were included in the analysis. The mean difference (MD), effect size (ES), and 95% confidence interval (CI) were estimated for visual analogue scale (VAS) scores, pain episode frequency, and the proportion of responders.

RESULTS

The analysis included 23 studies, including 4 RCTs, 14 single-arm studies, and 5 stratified studies. In the RCTs, BTX-A was found to significantly reduce mean VAS scores compared with baseline (ES: -4.05; 95% CI: -6.13, -1.97; P =0.002). In 19 non-RCTs, the pooled single-arm analysis revealed that BTX-A decreased VAS scores (ES: -5.19, 95% CI: -6.05, -4.33, P <0.001) and pain attack frequency (ES: -17.85, 95% CI: -23.36, -12.34, P <0.001) from baseline to the end of follow-up. The overall proportion of responders to BTX-A treatment was also significant (95% CI: 0.653, 0.761, P =0.003).

DISCUSSION

Current evidence indicates that BTX-A injection is an effective and safe option for patients with refractory TN or not responding to medical or surgical management. However, more high-quality studies are needed to further confirm its efficacy.

Pachyonychia Congenita: A Research Agenda Leading to New Therapeutic Approaches

Pachyonychia congenita (PC) is a dominantly inherited genetic disorder of cornification. PC stands out among other genodermatoses because despite its rarity, it has been the focus of a very large number of pioneering translational research efforts over the past 2 decades, mostly driven by a patient support organization, the Pachyonychia Congenita Project. These efforts have laid the ground for innovative strategies that may broadly impact approaches to the management of other inherited cutaneous and noncutaneous diseases. This article outlines current avenues of research in PC, expected outcomes, and potential hurdles.

Compared to oxcarbazepine and carbamazepine, botulinum toxin type A is a useful therapeutic option for trigeminal neuralgia symptoms: A systematic review

OBJECTIVES

This review aimed to compare the effectiveness of three treatments: BTX A, CBZ, and OXB, in managing trigeminal neuralgia (TN).

MATERIAL AND METHODS

We conducted a thorough search for research articles related to our issue using specific keywords on several databases, including Cochrane Central Register of Controlled Trials, Science Direct, Scopus, PubMed, Elsevier, Springer Journals, Ovid Medline, EBSCO, and Web of Science. Our focus was on publications from 1965 to 2023.

RESULTS

We retrieved 46 articles from the search and reviewed them carefully. Out of these, we selected 29 articles that met the inclusion criteria. Among the selected articles, 11 investigated the effects of CBZ and OXB, while 18 explored the impact of BTX A on the improvement of TN symptoms. The response rate ranged between 56% and 90.5% for CBZ and between 90.9% and 94% for OXB. The response rate for BTX A ranged between 51.4% and 100%. All these three treatments had a remarkable effect on the improvement of TN. Importantly, findings highlighted that side effects of CBZ and OXB could lead to treatment discontinuation in some cases, whereas BTX A's side effects have been minimal and less frequent.

CONCLUSIONS

Consequently, BTX A emerges as a promising alternative for TN treatment. However, additional clinical trials are necessary to validate this finding, and further research is required to establish a standardized protocol for administering BTX A in TN.

Differential Regulation of Intracisternally Injected Angiotensin II-Induced Mechanical Allodynia and Thermal Hyperalgesia in Rats

The present study examined the underlying mechanisms of mechanical allodynia and thermal hyperalgesia induced by the intracisternal injection of angiotensin (Ang) II. Intracisternal Ang II injection decreased the air puff threshold and head withdrawal latency. To determine the operative receptors for each distinct type of pain behavior, we intracisternally injected Ang II receptor antagonists 2 h after Ang II injection. Losartan, an Ang II type 1 receptor (AT1R) antagonist, alleviated mechanical allodynia. Conversely, PD123319, an Ang II type 1 receptor (AT2R) antagonist, blocked only thermal hyperalgesia. Immunofluorescence analyses revealed the co-localization of AT1R with the astrocyte marker GFAP in the trigeminal subnucleus caudalis and co-localization of AT2R with CGRP-positive neurons in the trigeminal ganglion. Intracisternal pretreatment with minocycline, a microglial inhibitor, did not affect Ang II-induced mechanical allodynia, whereas L-α-aminoadipate, an astrocyte inhibitor, significantly inhibited Ang II-induced mechanical allodynia. Furthermore, subcutaneous pretreatment with botulinum toxin type A significantly alleviated Ang II-induced thermal hyperalgesia, but not Ang II-induced mechanical allodynia. These results indicate that central Ang II-induced nociception is differentially regulated by AT1R and AT2R. Thus, distinct therapeutic targets must be regulated to overcome pain symptoms caused by multiple underlying mechanisms.

Botulinum toxin A and neuropathic pain: An update

Botulinum toxin type A is a widely used neurotoxin for the treatment of muscle hyperactivity such as dystonia and spasticity. Several clinical trials have also reported an efficacy of subcutaneous or intradermal administrations of botulinum toxin A on various neuropathic pain conditions including idiopathic trigeminal neuralgia and found that specific sensory phenotypes were predictors of the response. This narrative review summarizes the potential mechanisms of action, efficacy and safety of botulinum toxin A in neuropathic pain as well as its place in the therapeutic algorithm of neuropathic pain.

Targeting Nociceptive Neurons and Transient Receptor Potential Channels for the Treatment of Migraine

Migraine is a neurovascular disorder that affects approximately 12% of the global population. While its exact causes are still being studied, researchers believe that nociceptive neurons in the trigeminal ganglia play a key role in the pain signals of migraine. These nociceptive neurons innervate the intracranial meninges and convey pain signals from the meninges to the thalamus. Targeting nociceptive neurons is considered promising due to their accessibility and distinct molecular profile, which includes the expression of several transient receptor potential (TRP) channels. These channels have been linked to various pain conditions, including migraine. This review discusses the role and mechanisms of nociceptive neurons in migraine, the challenges of current anti-migraine drugs, and the evidence for well-studied and emerging TRP channels, particularly TRPC4, as novel targets for migraine prevention and treatment.

OnabotulinumtoxinA: Still the Present for Chronic Migraine

OnabotulinumtoxinA (BT-A) is one of the few drugs approved for the preventive treatment of chronic migraine (CM). Despite this, some aspects of its mechanism of action are still a matter of debate, and the precise magnitude of BT-A effects needs to be completely elucidated. BT-A acts primarily upon trigeminal and cervical nerve endings, by inhibiting the release of inflammatory mediators such as calcitonin gene-related peptide, as well as reducing the insertion of ionotropic and metabotropic receptors into the neuronal membrane. These actions increase the depolarization threshold of trigeminal and cervical nerve fibers, thus reducing their activation. The central actions of BT-A are still a matter of debate: a retrograde axonal transport has been postulated, but not clearly assessed in humans. Clinically, the efficacy of BT-A in CM has been assessed by large, randomized placebo-controlled trials, such as the Phase 3 REsearch Evaluating Migraine Prophylaxis Therapy (PREEMPT) trials. Those results were also confirmed in a wide range of open-label studies, even for long-term periods. Recently, novel findings have led to a better understanding of its pharmacological actions and clinical usefulness in migraine prevention. This narrative review summarizes, updates and critically revises the available data on BT-A and its possible implementation in chronic migraine. Moreover, the current role of BT-A in CM treatment has been discussed.

OnabotulinumtoxinA Treatment in Chronic Migraine: Investigation of Its Effects on Disability, Headache and Neck Pain Intensity

Neck disability and pain are frequently encountered problems in patients with chronic migraine (CM). The long-term stimuli of neurons in the trigeminocervical junction may explain this situation. OnabotulinumtoxinA (ONA) treatment is one of the proven treatments for CM; however, there is no study data on the efficacy of ONA treatment on neck disability and pain in CM patients. Therefore, we aimed to investigate the effect of ONA treatment on disability, neck pain and headache intensity in CM patients. One hundred thirty-four patients who met the inclusion criteria were included in the study. ONA treatment was administered at a dose of 195 U to 39 sites in total as per Follow-the-Pain PREEMPT protocol. The disability was evaluated with the Neck Disability Index and the Migraine Disability Assessment; pain intensity was evaluated with the Visual Analogue Scale; the monthly number of headache days were recorded; quality of life was evaluated with the Headache Impact Test. All assessments were recorded at baseline and 3 months after treatment. After the treatment, neck−migraine disabilities decreased from severe to mild for neck and moderate for migraine (p < 0.001). Neck pain and headache intensities decreased by almost half (p < 0.001). The median number of monthly headache days decreased from 20 days to 6 days (p < 0.000). The quality-of-life level decreased significantly from severe to substantial level (p < 0.001). According to our results, ONA treatment was effective in reducing neck-related problems in CM patients. Long-term follow-up results may provide researchers with more comprehensive results in terms of the treatment of chronic migraine−neck-related problems.

How Does Botulinum Toxin Inhibit Itch?

Two decades after reports of the anti-pruritic effects of botulinum neurotoxins (BoNTs), there is still no approved product for the anti-itch indication of BoNTs, and most clinical case reports still focus on the off-label use of BoNTs for various itchy conditions. Few randomized clinical trials have been conducted with controversial results, and the beneficial effects of BoNTs against itch are mainly based on case studies and case series. These studies are valuable in presenting the potential application of BoNTs in chronic pruritic conditions, but due to the nature of these studies, they are categorized as providing lower levels of evidence or lower grades of recommendation. To obtain approval for the anti-pruritic indication of BoNTs, higher levels of evidence are required, which can be achieved through conducting large-scale and well-designed studies with proper control groups and established careful and reliable primary and secondary outcomes. In addition to clinical evidence, presenting the mechanism-based antipruritic action of BoNTs can potentially strengthen, accelerate, and facilitate the current efforts towards further investments in accelerating the field towards the potential approval of BoNTs for itchy conditions. This review, therefore, aimed to provide the state-of-the-art mechanisms underlying the anti-itch effect of BoNTs from basic studies that resemble various clinical conditions with itch as a hallmark. Evidence of the neuronal, glial, and immune modulatory actions of BoNTs in reducing the transmission of itch are presented, and future potential directions are outlined.

Generalized Anxiety Disorder: A Predictor for Poor Responsiveness to Botulinum Toxin Type A Therapy for Pediatric Migraine

BACKGROUND

To assess the efficacy, safety, and predictors for poor responsiveness of botulinum toxin type A (BoNT-A) for chronic migraine in the adolescent and young adult population.

METHODS

A retrospective analysis of 56 patients who received BoNT-A for chronic migraine with an age range from 13 to 21 years was performed. Of 56 patients, 34 were enrolled in the study based on the inclusion criterion. Patients who received three dosages of BoNT-A were assessed at nine months from the first injection. Variables including age, body mass index, headache intensity, frequency, character, and side effects were assessed. The patients were divided into two groups based on response to BoNT-A therapy, responders and nonresponders.

RESULTS

Overall among the 34 patients enrolled in the study, the average headache frequency decreased from 18.6 of 28 to 9.9 of 28 days, P value, <0.001 from baseline. There was significant decrease in the average headache intensity, 8.1 to 4.3. Of 34 patients, 25 (73%) patients responded to treatment with decrease in headache frequency by ≥ 50% from the baseline. Among the nonresponder patients, a significant number of patients (six of nine, 67%) had generalized anxiety disorder with Generalized Anxiety Disorder-7 score greater than 15 versus the responder group (six of 25, 24%, P value 0.040).

CONCLUSIONS

BoNT-A remains a safe and effective therapy for adolescent and young adult patients with chronic migraines at nine months of follow-up. Generalized anxiety disorder with Generalized Anxiety Disorder-7 score greater than 15 can be a major predictor of poor response to this therapy.

Transient Receptor Potential Channels and Botulinum Neurotoxins in Chronic Pain

Pain afflicts more than 1.5 billion people worldwide, with hundreds of millions suffering from unrelieved chronic pain. Despite widespread recognition of the importance of developing better interventions for the relief of chronic pain, little is known about the mechanisms underlying this condition. However, transient receptor potential (TRP) ion channels in nociceptors have been shown to be essential players in the generation and progression of pain and have attracted the attention of several pharmaceutical companies as therapeutic targets. Unfortunately, TRP channel inhibitors have failed in clinical trials, at least in part due to their thermoregulatory function. Botulinum neurotoxins (BoNTs) have emerged as novel and safe pain therapeutics because of their regulation of exocytosis and pro-nociceptive neurotransmitters. However, it is becoming evident that BoNTs also regulate the expression and function of TRP channels, which may explain their analgesic effects. Here, we summarize the roles of TRP channels in pain, with a particular focus on TRPV1 and TRPA1, their regulation by BoNTs, and briefly discuss the use of BoNTs for the treatment of chronic pain.

Experiences on The Administration of Botulinum Toxin in Movement Disorders

Background and objectives

Botulinum toxin injection has been used for many years for various indications such as cervical dystonia, blepharospasm, oromandibular dystonia, hemifacial spasm in neurology. Botulinum toxin injections have been made in our clinic for about ten years. We want to report our experiences about botulinum toxin treatment in neurologic disease.

Methods

In this study, the data of the patients receiving BoNT injection between January 2018 and December 2019 was retrospectively analyzed. Age, gender, botulinum toxin indications, and mean dose, duration of efficacy, side effects noted for each injection were recorded.

Results

There were 122 patients who received botulinum toxin injections between January 2018 and December 2019. Of the 122 patients identified, 28 had cervical dystonia, 61 had HFS, 21 had blepharospasm, 4 had generalized dystonia, 1 had hemidystonia following thalamic bleeding, 1 had tardive dystonia, 4 had migraine, 1 had bruxism and 1 had both migraine and bruxism.

Conclusion

BoNT injection is a treatment that has been used for various indications in neurology for almost 40 years. Side effects are limited and temporary with appropriate injections. We also had a wide range of indication profiles and high numbers of patients to whom we administered the BoNT treatment.

Mechanism of Action of OnabotulinumtoxinA in Chronic Migraine: A Narrative Review

Objective

To review the literature on the mechanism of action of onabotulinumtoxinA in chronic migraine.

Background

OnabotulinumtoxinA is a chronic migraine preventive treatment that significantly reduces headache frequency. The traditional mechanism described for onabotulinumtoxinA – reducing muscle contractions – is insufficient to explain its efficacy in migraine, which is primarily a sensory neurological disease.

Methods

A narrative literature review on the mechanism of action of onabotulinumtoxinA in chronic migraine.

Results

Following injection into tissues, onabotulinumtoxinA inhibits soluble N‐ethylmaleimide‐sensitive fusion attachment protein receptor (SNARE)‐mediated vesicle trafficking by cleaving one of its essential proteins, soluble N‐ethylmaleimide‐sensitive fusion attachment protein (SNAP‐25), which occurs in both motor and sensory nerves. OnabotulinumtoxinA inhibits regulated exocytosis of motor and sensory neurochemicals and proteins, as well as membrane insertion of peripheral receptors that convey pain from the periphery to the brain, because both processes are SNARE dependent. OnabotulinumtoxinA can decrease exocytosis of pro‐inflammatory and excitatory neurotransmitters and neuropeptides such as substance P, calcitonin gene‐related peptide, and glutamate from primary afferent fibers that transmit nociceptive pain and participate in the development of peripheral and central sensitization. OnabotulinumtoxinA also decreases the insertion of pain‐sensitive ion channels such as transient receptor potential cation channel subfamily V member 1 (TRPV1) into the membranes of nociceptive neurons; this is likely enhanced in the sensitized neuron. For chronic migraine prevention, onabotulinumtoxinA is injected into 31‐39 sites in 7 muscles of the head and neck. Sensory nerve endings of neurons whose cell bodies are located in trigeminal and cervical ganglia are distributed throughout the injected muscles, and are overactive in people with migraine. Through inhibition of these sensory nerve endings, onabotulinumtoxinA reduces the number of pain signals that reach the brain and consequently prevents activation and sensitization of central neurons postulated to be involved in migraine chronification.

Conclusion

OnabotulinumtoxinA likely acts via sensory mechanisms to treat chronic migraine.

The fifth cranial nerve in headaches

The fifth cranial nerve is the common denominator for many headaches and facial pain pathologies currently known. Projecting from the trigeminal ganglion, in a bipolar manner, it connects to the brainstem and supplies various parts of the head and face with sensory innervation. In this review, we describe the neuroanatomical structures and pathways implicated in the sensation of the trigeminal system. Furthermore, we present the current understanding of several primary headaches, painful neuropathies and their pharmacological treatments. We hope that this overview can elucidate the complex field of headache pathologies, and their link to the trigeminal nerve, to a broader field of young scientists.

Post-Burn Pruritus

Post-burn pruritus is the pruritus that occurs after burn during the rehabilitation and healing process of burn wounds. The post-burn pruritus is a common and serious complication of burn injury, which severely lowers the quality of life of the patient. Many potential treatments are available for pruritus but there is no consensus of the best single treatment yet. The precise mechanism of post-burn pruritus has not been elucidated, but it appears to have pruritogenic and neuropathic aspects. Clinically, post-burn pruritus tends to be intractable to conventional treatment but rather responds to neuroleptic agents, such as gabapentin and pregabalin. During wound healing, various neuropeptides secreted from the nerves of the skin control epidermal and vascular proliferation and connective tissue cells. When keratinocytes are activated by an itch-inducing substance, they secrete a variety of inflammatory substances that increase the susceptibility of the itch receptor. There are two mechanisms underlying post-burn neuropathic pruritus. The first one is peripheral sensitization. The second one is the intact nociceptor hypothesis. An effective treatment for post-burn pruritus will also be effective in other neuropathic and intractable itching. In this review, we summarized the interaction and mechanism of keratinocytes, immune cells, and nerve fibers related to post-burn pruritus.

Dual Therapy With Anti-CGRP Monoclonal Antibodies and Botulinum Toxin for Migraine Prevention: Is There a Rationale?

OBJECTIVE

To narratively review the pathophysiological rationale of dual therapy with anti-calcitonin gene-related peptide monoclonal antibodies and botulinum toxin type A in treatment-resistant chronic migraine prevention.

BACKGROUND

For the prevention of chronic migraine, several pharmacological therapies are available, including oral medications, botulinum toxin type A, and the newly approved monoclonal antibodies targeting calcitonin gene-related peptide or its receptor. However, monotherapy does not yield benefits in some affected individuals, which raises the question of whether dual therapy with monoclonal antibodies and botulinum toxin type A hold promise in patients with treatment-resistant chronic migraine.

METHOD

We searched MEDLINE for articles published from database inception to December 31st, 2019. Publications were largely selected from the past 10 years but commonly referenced and highly regarded older publications were not excluded.

RESULTS

Preclinical data suggest that anti-calcitonin gene-related peptide monoclonal antibodies and botulinum toxin type A have synergistic effects within the trigeminovascular system. Of note, findings indicate that fremanezumab - an antibody targeting the calcitonin gene-related peptide - mainly prevents the activation of Aδ-fibers, whereas botulinum toxin type A prevents the activation of C-fibers.

CONCLUSION

There is currently only indirect preclinical evidence to support a rationale for dual therapy with anti-calcitonin gene-related peptide monoclonal antibodies and botulinum toxin type A for chronic migraine prevention. Rigorous studies evaluating clinical efficacy, safety, and cost-effectiveness are needed.

Modifications to the PREEMPT Protocol for OnabotulinumtoxinA Injections for Chronic Migraine in Clinical Practice

OBJECTIVE

To assess the PREEMPT protocol modifications that have developed in clinical practice over time.

BACKGROUND

The United States Food and Drug Administration approved the 155-unit fixed-dose, fixed-site PREEMPT protocol of onabotulinumtoxinA (BoNT-A) injections for migraine prevention 9 years ago.

METHODS

This is an anonymous survey with free text response options of Headache Medicine clinicians.

RESULTS

Out of the 878 contacted Headache Medicine clinicians, 182 (20.7%) completed the survey. Of the 182 respondents, 141 (77.5%) reported that they did not always follow the PREEMPT protocol. Of the 182 respondents, 128 (70%) changed the number of injections, 115 (63%) changed the total units of BoNT-A injected, 105 (57.7%) altered the location of injection sites (58%); 101 (55.5%) do not aspirate to ensure the absence of blood return; 22 (12.1%) changed the dilution; and 4 (2.2%) added lidocaine. The main reported reasons for changes in number, dose, and location of injections included adapting to the patients' pain, anatomy, and preferences.

CONCLUSIONS

The wide inter- and intra-personal variations in BoNT-A injections for chronic migraine prevention seen in this survey raise concerns about the standardization of the procedure and suggest that an advisory protocol containing more evidence and discussion of the reasoning behind the recommendations might be more helpful than the current prescriptive protocol.

Botulinum toxin for facial neuralgia

Data sourcesMedline via PubMed, the Web of Science and the Cochrane Library were searched until April 2014.Study selectionRandomised controlled trials (RCTs) comparing the efficacy of botulinum toxin type A (BoTN-A) with placebo in patients with painful trigeminal (TN) and postherpetic neuralgia (PHN) reporting changes in pain intensity in patients aged 19 years and older available in English were included.Data extraction and synthesisThree authors independently assessed for inclusion, extracted standard data and assessed for risk of bias. The primary outcomes were baseline and post treatment intensity of pain and patients reporting pain relief of 50% or greater.For continuous outcomes the treatment effect was measured as mean differences with 95% confidence intervals (CIs). For dichotomous outcome of reduction of pain of 50% or more, relative risk (risk ratio) with 95% CIs was reported. Statistical heterogeneity was tested with Cochran's test for heterogeneity and quantified by the I2 statistic. Results were combined using random-effects model in the presence of statistical heterogeneity otherwise fixed effect model was used.ResultsSix studies were included. The effects of the interventions were presented in three meta-analyses. Mean difference in post treatment pain (six studies) pooled results showed a reduction of -3.009 in the VAS (95% CI -4.566 to -1.453 p<0.001) with the use of BoTN-A. Standardised difference in mean post treatment pain (six studies) was -0.918 (95% CI -1.197 to -0.639 p<0.001) in favor of BoTN-A. For the percentage of patients experiencing 50% pain reduction (three studies) absolute risk difference and relative risk were calculated (RR 2.892, 95% CI 1.726 to 4.848 p<0.001) in favour of the use of BoTN-A.ConclusionsThe authors concluded that there is moderate evidence regarding the efficacy of BoTN-A in treating patients with trigeminal neuralgia and postherpetic neuralgia.

The Use of Botulinum Toxin in the Management of Headache Disorders

Tremendous progress has been made in the past decades for the treatment of headache disorders. Chronic migraine is the most disabling type of headache and requires the use of acute and preventive medications, many of which are associated with adverse events that limit patient adherence. Botulinum toxin (BoNT) serotype A, a neurotoxin derived from certain strains of Clostridium, disrupts neuropeptide secretion and receptor translocation related to trigeminal nociception, thereby preventing pain sensitization through peripheral and possibly central mechanisms. Ever since the first randomized controlled trial on onabotulinumtoxinA (onabotA) for migraine was published two decades ago, onabotA has been the only BoNT formulation approved for use in the prevention of chronic migraine. Superior tolerability and efficacy have been demonstrated on multiple migraine endpoints in many controlled trials and real-life studies. OnabotA is a safe and efficacious treatment for chronic migraine and possibly high-frequency episodic migraine. Further research is still needed to understand its mechanism of action to fully develop its therapeutic potential.

Perineural injection of botulinum toxin-A in painful peripheral nerve injury - a case series: pain relief, safety, sensory profile and sample size recommendation

Objectives: Subcutaneous injection of botulinum toxin-A (sBONT-A) is a novel treatment for peripheral neuropathic pain. While its analgesic effects are well documented, this treatment is often not comfortable and fails in patients who show signs of sensory loss but rarely allodynia. There are some case reports about perineural BONT-A injection (pBONT-A) which could be an alternative approach. Here we present a retrospective, open label case series of pBONT-A's efficacy and safety regarding neurological consequences involving changes in somatosensory profiles of both responders and non-responders. Methods: Sixty patients (53 ± 13years, 77% males) with PNI were treated with pBONT-A after a test injection with a local anesthetic, which prompted distinctive pain relief. Quantitative sensory testing (QST; DFNS protocol) and pain intensity were assessed before and ≥7 days post pBONT-A injection. Definition of response: satisfactory pain reduction of ≥30% NRS (numerical rating scale: 0 = no pain, 10 = worst pain) for ≥4 days. Statistics: Paired t-test, Mann-Whitney U-test, χ² test. Results: A temporary weak paresis in one case was clinically verified. The QST -parameters remained unchanged, but patients with more frequent hyperalgesia signs reported less analgesia (p = .04). The pBONT-A injection prompted pain relief by 24.8% (NRS: 6.0 ± 1.7 vs. 4.5 ± 2.1; p < .0001); 57% (n = 34) were responders (NRS: 6.0 ± 1.6 vs. 3.4 ± 1.6, relief of 43.4%; p < .0001). Based on these results, we suggest that future parallel design trials on pBONT-A need to include at least 84 patients. Discussion: Ultrasound-guided pBONT-A injection seems to be a safe treatment leading to a sufficient pain relief for some months without sensory changes. Surprisingly, pBONT-A showed a pronounced analgesic effect also in patients without signs of hyperalgesia.

Factors affecting the therapeutic effect of botulinum toxin A on trigeminal neuralgia: A follow-up retrospective study of 152 patients

Botulinum toxin A (BTX-A) is a promising therapeutic modality against trigeminal neuralgia (TN) with certain controversies pertaining to its application. To provide further information on factors influencing the treatment outcomes of BTX-A, a retrospective study with 152 patients with TN treated with BTX-A was performed. The starting time and duration of the therapeutic effect, as well as side effects, of BTX-A in the treatment of TN were analyzed by sex, age, course of disease, number of branches and injected dose. A total of 136 patients exhibited symptom improvement within 2 weeks following BTX-A treatment as evaluated using a visual analog scale (VAS). The effect of BTX-A was sustained throughout the initial 6 months of the follow-up and was demonstrated to persist for as long as 28 months. Female sex, short disease course and high injection dose (>70 units) were associated with lower long-term VAS scores. Patients receiving short-term medium-(50–70 units) or high-dose injections were more likely to be completely cured. Patients with a median disease course (1–10 years) or multiple branches were more likely to exhibit facial asymmetry. Based on the stratified analysis, female patients with a median disease course (1–10 years) exhibited a higher incidence of side effects and male patients achieved better treatment outcomes with high BTX-A doses. BTX-A effectively alleviated patients with TN in both short or long term, although the treatment efficacy may depend on patient characteristics.

Exploring the effects of extracranial injections of botulinum toxin type A on prolonged intracranial meningeal nociceptors responses to cortical spreading depression in female rats

Background

Botulinum neurotoxin type A, an FDA-approved prophylactic drug for chronic migraine, is thought to achieve its therapeutic effect through blocking activation of unmyelinated meningeal nociceptors and their downstream communications with myelinated nociceptors and potentially the vasculature and immune cells. Prior investigations to determine botulinum neurotoxin type A effects on meningeal nociceptors were carried out in male rats and tested with stimuli that act outside the blood brain barrier. Here, we sought to explore the effects of extracranial injections of botulinum neurotoxin type A on activation of meningeal nociceptors by cortical spreading depression, an event which occurs inside the blood brain barrier, in female rats.

Material and methods

Using single-unit recording, we studied myelinated C- and unmyelinated Aδ-meningeal nociceptors' responses to cortical spreading depression 7–14 days after injection of botulinum neurotoxin type A or saline along calvarial sutures.

Results

In female rats, responses to cortical spreading depression were typically more prolonged and, in some cases, began at relatively longer latencies post-cortical spreading depression, than had been observed in previous studies in male rats. Extracranial administration of botulinum neurotoxin type A reduced significantly the prolonged firing of the meningeal nociceptors, in the combined sample of Aδ- and C-fiber, but not their response probability.

Discussion

The findings suggest that the mechanism of action by which botulinum neurotoxin type A prevents migraine differ from the one by which calcitonin gene-related peptide monoclonal antibodies prevent migraine and that even when the origin of migraine is central (i.e. in the cortex), a peripherally acting drug can intercept/prevent the headache.

Botulinum Toxin a Valuable Prophylactic Agent for Migraines and a Possible Future Option for the Prevention of Hormonal Variations-Triggered Migraines

BACKGROUND

In 1989, Botulinum toxin (BoNT) was accepted by the FDA for the management of some ophthalmic disorders. Although it was initially considered a lethal toxin, in recent times, Botulinum toxin A (BoNT-A), which is the more used serotype, has expanded to cover different clinical conditions, primarily characterized by neuropathic pain, including migraines and headaches. Evidence suggests that migraines are influenced by hormonal factors, particularly by estrogen levels, but very few studies have investigated the prevalence and management strategies for migraines according to the hormonal status. The effects of several therapeutic regimens on migraines have been investigated, but the medications used varied widely in proven efficacies and mechanisms of action. BoNT-A is increasingly used in the management of migraine and several placebo-controlled trials of episodic and chronic migraine are currently underway. This paper is a review of the recently published data concerning the administration of BoNT-A in the prevention of chronic migraines. Considering the lack of population-based studies about the effectiveness of BoNT-A in the alleviation of premenstrual and perimenopausal migraines, this study proposes a new perspective of the therapeutic approach of migraine syndrome associated with menopausal transition and the premenstrual period.

METHODS

We selected the reviewed papers from CrossRef, PubMed, Medline, and GoogleScholar, and a total of 21 studies met our inclusion criteria.

RESULTS

To date, no specific preventive measures have been recommended for menopausal women with migraines. BoNT-A often reduces the frequency and intensity of migraine attacks per month; the treatment is well tolerated and does not exhibit a significantly higher rate of treatment-related side effects. No population-based studies were conducted in order to highlight the role of BoNT-A in menopause-related migraines, neither in menstrual migraines.

CONCLUSION

There is a need for further research in order to quantify the real burden of menstrual and perimenopausal migraines and to clarify if BoNT-A could be used in the treatment of refractory postmenopausal and premenstrual migraines.

Mechanisms of Botulinum Toxin Type A Action on Pain

Already a well-established treatment for different autonomic and movement disorders, the use of botulinum toxin type A (BoNT/A) in pain conditions is now continuously expanding. Currently, the only approved use of BoNT/A in relation to pain is the treatment of chronic migraines. However, controlled clinical studies show promising results in neuropathic and other chronic pain disorders. In comparison with other conventional and non-conventional analgesic drugs, the greatest advantages of BoNT/A use are its sustained effect after a single application and its safety. Its efficacy in certain therapy-resistant pain conditions is of special importance. Novel results in recent years has led to a better understanding of its actions, although further experimental and clinical research is warranted. Here, we summarize the effects contributing to these advantageous properties of BoNT/A in pain therapy, specific actions along the nociceptive pathway, consequences of its central activities, the molecular mechanisms of actions in neurons, and general pharmacokinetic parameters.

OnabotulinumtoxinA wear-off in chronic migraine, observational cohort study

INTRODUCTION

The current standard-of-care protocol for OnabotulinumtoxinA (BoNTA) injections consists of fixed-site injections every 12 weeks. This pattern is based on clinical practice and extrapolated from BoNTA injections for other, non-migraine-related indications. It is unclear if this protocol is optimal for chronic migraine. In clinical practice, migraine patients frequently describe a period of increased headache frequency and intensity in the few weeks preceding their next injections. In order to evaluate the duration of the clinical effect of BoNTA injections in chronic migraine, we studied the variation in headache frequency on a weekly basis during the 12-week period following treatment in a cohort of migraine patients.

METHOD

38 consecutive subjects were enrolled from an outpatient headache clinic, and asked to keep daily headache journals. 24 completed headache journals were analyzed. Headache frequency, duration and severity, as well as intake of symptomatic headache medications were recorded and compared among the different weeks.

RESULTS

The time-response plot following BoNTA injection was roughly U-shaped, with 3 distinct phases: an induction phase, a maximum efficacy phase, and a wear-off phase. The time-response plot revealed that the wear-off commenced around the eighth week post injection. The mean difference in the number of headache days per week between the first and the eighth week was 1.8 (95% CI [0.670-2.830], p = 0.003).

CONCLUSION

The effect of BoNTA injections on chronic migraines was not uniform throughout a 12-week period. A window of vulnerability to migraine attacks exist in the beginning and end of each cycle.

Studies on the Activity of Selected Highly Lipophilic Compounds toward hGAT1 Inhibition. Part II

In this paper, we describe the latest results involving molecular modeling and pharmacodynamic studies of the selected highly lipophilic compounds acting by human GABA transporter 1 (hGAT1) inhibition. The chemical interaction of 17 GABA analogues with a model of hGAT1 is described using the molecular docking method. The biological role of GAT1 is related to the regulation of GABA level in the central nervous system and GAT1 inhibition plays an important role in the control of seizure threshold. To confirm that GAT1 can be also a molecular target for drugs used to treat other neurological and psychiatric diseases (e.g., pain and anxiety), in the in vivo part of this study, potential antinociceptive and anxiolytic-like properties of tiagabine, a selective GAT1 inhibitor, are described.

Botulinum neurotoxin type A combined with functional electrical stimulation for upper-limb poststroke spasticity with pain

Stroke is a complicated condition that leaves stroke survivors with prolonged disability. Common poststroke conditions are spasticity and pain, which directly affect daily activities and quality of life in these patients. Botulinum neurotoxin type A is an effective and well-tolerated treatment option for upper-limb spasticity. It reduces muscle tone and improves basic upper-limb activities. Functional electrical stimulation is also used widely as a therapeutic modality in the upper-limb muscle rehabilitation. Here, we present a case in which Botulinum neurotoxin type A injections combined with functional electrical stimulation were applied for upper-limb spasticity accompanied with pain in a poststroke patient.

Guideline on the use of onabotulinumtoxinA in chronic migraine: a consensus statement from the European Headache Federation

OnabotulinumtoxinA is being increasingly used in the management of chronic migraine (CM). Treatment with onabotulinumtoxinA poses challenges compared with traditional therapy with orally administered preventatives. The European Headache Federation identified an expert group that was asked to develop the present guideline to provide recommendations for the use of onabotulinumtoxinA in CM. The expert group recommend onabotulinumtoxinA as an effective and well-tolerated treatment of CM. Patients should preferably have tried two to three other migraine prophylactics before start of onabotulinumtoxinA. Patients with medication overuse should be withdrawn from the overused medication before initiation of onabotulinumtoxinA if feasible, if not onabotulinumtoxinA can be initiated from the start or before withdrawal. OnabotulinumtoxinA should be administered according to the PREEMPT injection protocol, i.e. injecting 155 U–195 U to 31–39 sites every 12-weeks. We recommend that patients are defined as non-responders, if they have less than 30% reduction in headache days per month during treatment with onabotulinumtoxinA. However other factors such as headache intensity, disability and patient preferences should also be considered when evaluating response. Treatment should be stopped, if the patient does not respond to the first two to three treatment cycles. Response to continued treatment with onabotulinumtoxinA should be evaluated by comparing the 4 weeks before with the 4 weeks after each treatment cycle. It is recommended that treatment is stopped in patients with a reduction to less than 10 headache days per month for 3 months and that patients are re-evaluated 4–5 months after stopping onabotulinumtoxinA to make sure that the patient has not returned to CM. Questions regarding efficacy and tolerability of onabotulinumtoxinA could be answered on the basis of scientific evidence. The other recommendations were mainly based on expert opinion. Future research on the treatment of CM with onabotulinumtoxinA may further improve the management of this highly disabling disorder.

TRPV1-Like Immunoreactivity in the Human Locus K, a Distinct Subregion of the Cuneate Nucleus

The presence of transient receptor potential vanilloid type-1 receptor (TRPV1)-like immunoreactivity (LI), in the form of nerve fibres and terminals, is shown in a set of discrete gray matter subregions placed in the territory of the human cuneate nucleus. We showed previously that those subregions share neurochemical and structural features with the protopathic nuclei and, after the ancient name of our town, collectively call them Locus Karalis, and briefly Locus K. TRPV1-LI in the Locus K is codistributed, though not perfectly overlapped, with that of the neuropeptides calcitonin gene-related peptide and substance P, the topography of the elements immunoreactive to the three markers, in relation to each other, reflecting that previously described in the caudal spinal trigeminal nucleus. Myelin stainings show that myelinated fibres, abundant in the cuneate, gracile and trigeminal magnocellular nuclei, are scarce in the Locus K as in the trigeminal substantia gelatinosa. Morphometric analysis shows that cell size and density of Locus K neurons are consistent with those of the trigeminal substantia gelatinosa and significantly different from those of the magnocellular trigeminal, solitary and dorsal column nuclei. We propose that Locus K is a special component of the human dorsal column nuclei. Its functional role remains to be determined, but TRPV1 appears to play a part in it.

Evaluation of OnabotulinumtoxinA Treatment in Patients with Concomitant Chronic Migraine and Temporomandibular Disorders

Introduction

Migraine and temporomandibular disorders (TMD) are both common diseases and TMD are reported as a risk factor in migraine progression. OnabotulinumtoxinA is used in the treatment of chronic migraine (CM), and also has a potential role in TMD treatment. In this study, it is aimed to compare the efficacy of onabotulinumtoxinA treatment in CM patients with and without TMD.

Methods

In this retrospective study, 30 CM patients (age range: 18-65 years), satisfying the inclusion and follow-up criteria in their medical records were investigated. The PREEMPT injection protocol was taken as reference and onabotulinumtoxinA 155-195 U with fixed-dose has been administered into 31 specific sites within the head/neck muscles in included subjects. Two cycles of treatment were assessed in all patients at the baseline and 12 weeks later. The headache diaries, which were completed routinely one month before, and during 6 months follow-up after the treatment, were assessed. The effect of onabotulinumtoxinA treatment was compared between CM patients with and without TMD/bruxism.

Results

Of 30 female patients, 17 had concomitant TMD. In week 24, there were significant improvement in the groups with and without TMD regarding to the mean change of frequencies in the days with migraine compared to the initial findings (p<0.001). However, there was no significant difference between the two groups.

Conclusions

OnabotulinumtoxinA is an effective and safe treatment for CM. Its efficacy appears to be similar in CM patients with and without TM, speculating that the comorbidity of TMD did not play a role for the treatment response.

Botulinum toxin: A review of the mode of action in migraine

Botulinum toxin serotype A (BoNT/A) was originally used in neurology for the treatment of dystonia and blepharospasms, but is now clinically used worldwide for the treatment of chronic migraine. Still, the possible mode of action of BoNT/A in migraine is not fully known. However, the mode of action of BoNT/A has been investigated in experimental pain as well as migraine models, which may elucidate the underlying mechanisms in migraine. The aim of this study was to review studies on the possible mode of action of BoNT/A in relation to chronic migraine treatment. Observations suggest that the mode of action of BoNT/A may not be limited to the injection site, but also includes anatomically connected sites due to axonal transport. The mechanisms behind the effect of BoNT/A in chronic migraine may also include modulation of neurotransmitter release, changes in surface expression of receptors and cytokines as well as enhancement of opioidergic transmission. Clinical and experimental studies with botulinum toxin in the last decade have advanced our understanding of headache and other pain states. More research into botulinum toxin as treatment for headache is warranted as it can be an attractive alternative for patients who do not respond positively to other drugs.

Current Prophylactic Medications for Migraine and Their Potential Mechanisms of Action

A relatively high number of different medications is currently used for migraine prevention in clinical practice. Although these compounds were initially developed for other indications and differ in their mechanisms of action, some general themes can be identified from the mechanisms at play. Efficacious preventive drugs seem to either suppress excitatory nervous signaling via sodium and/or calcium receptors, facilitate GABAergic inhibition, reduce neuronal sensitization, block cortical spreading depression and/or reduce circulating levels of CGRP. We here review such mechanisms for the different compounds.

Antipruritic Effects of Botulinum Neurotoxins

This review explores current evidence to demonstrate that botulinum neurotoxins (BoNTs) exert antipruritic effects. Both experimental and clinical conditions in which botulinum neurotoxins have been applied for pruritus relief will be presented and significant findings will be highlighted. Potential mechanisms underlying antipruritic effects will also be discussed and ongoing challenges and unmet needs will be addressed.

Botulinum Toxin Type A Injection for Neuropathic Pain in a Patient With a Brain Tumor: A Case Report

Neuropathic pain is usually managed pharmacologically, rather than with botulinum toxin type A (BTX-A). However, medications commonly fail to relieve pain effectively or have intolerable side effects. We present the case of a 62-year-old man diagnosed with an intracranial chondrosarcoma, which was removed surgically and treated with radiation therapy. He suffered from neuropathic pain despite combined pharmacological therapy with gabapentin, amitriptyline, tramadol, diazepam, and duloxetine because of adverse effects. BTX-A (100 units) was injected subcutaneously in the most painful area in the posterior left thigh. Immediately after the injection, his pain decreased significantly from 6/10 to 2/10 on a visual analogue scale. Pain relief lasted for 12 weeks. This case report describes intractable neuropathic pain caused by a brain tumor that was treated with subcutaneous BTX-A, which is a useful addition for the management of neuropathic pain related to a brain tumor.

Botulinum Toxin in the Field of Dermatology: Novel Indications

Since its approval by the US Food and Drug Administration in 2002 for glabellar wrinkles, botulinum toxin (BTX) has been widely used to correct facial wrinkles. As a result, many consider BTX synonymous with cosmetic dermatology. Recent studies indicate that BTX elicits biological effects on various skin cell types via the modulation of neurotransmitter release, and it seems that BTX has a wider zone of dermatologic influence than originally understood. Clinicians and researchers are now beginning to explore the potential of BTX beyond the amelioration of facial lines and encouraging results are seen with BTX in a variety of skin conditions. In this paper, we review novel dermatological indications of BTX which includes (but not limited to) scar prevention, facial flushing, post-herpetic neuralgia and itch. These areas show great promise, but there is definite need for larger, double-blinded, randomized control trials against established treatments before BTX becomes a clinical reality.

Botulinum neurotoxin type-A when utilized in animals with trigeminal sensitization induced a antinociceptive effect

METHOD

Neuropathic pain was induced by surgical constriction of the infraorbital nerve in rats. A control group underwent a sham procedure consisting of surgical exposure of the nerve. Subgroups of each group received either BoNT/A or isotonic saline solution. The clinical response was assessed with the -20°C test. Animals that underwent nerve constriction developed sensitization; the sham group did not.

RESULTS

The sensitization was reversed by BoNT/A treatment evident 24 hours following application. Pronociceptive effect was observed in the sham group following BoNT/A.

CONCLUSION

BoNT/A has an antinociceptive effect in sensitized animals and a pronociceptive effect in non-sensitized animals.

[Botulinum toxin type A in headache treatment : Established and experimental indications]

In recent years botulinum toxin type A has been used increasingly more in the treatment of specific headache disorders. Especially regarding chronic migraine with and without combined medication overuse, convincing randomized studies have proven the efficacy of this treatment option and have led to approval for this indication. Regarding other headache entities, such as episodic migraine, tension-type headache, trigeminal autonomic cephalalgia (TAC), neuralgic, neuropathic and myofascial pain, currently available scientific data on the efficacy of botulinum toxin type A are scarce and often ambiguous. The exact underlying mechanisms of the influence of botulinum toxin type A on the pathophysiology of headache are not completely clear but an influence on the release of calcitonin gene-related peptide (CGRP) seems to play a crucial role. This article summarizes the most important studies as well as experiences of treatment with botulinum toxin type A regarding different headache entities.

Nonparalytic botulinum molecules for the control of pain

BiTox attenuated A-nociceptor-mediated mechanosensitivity in rat models of chronic pain. Plasma extravasation and keratinocyte proliferation were also inhibited but C-fiber nociception was not impaired.

Local injections of botulinum toxins have been reported to be useful not only for the treatment of peripheral neuropathic pain and migraine but also to cause long-lasting muscle paralysis, a potentially serious side effect. Recently, a botulinum A-based molecule (“BiTox”) has been synthesized that retains neuronal silencing capacity without triggering muscle paralysis. In this study, we examined whether BiTox delivered peripherally was able to reduce or prevent the increased nociceptive sensitivity found in animal models of inflammatory, surgical, and neuropathic pain. Plasma extravasation and edema were also measured as well as keratinocyte proliferation. No motor deficits were seen and acute thermal and mechanical nociceptive thresholds were unimpaired by BiTox injections. We found reduced plasma extravasation and inflammatory edema as well as lower levels of keratinocyte proliferation in cutaneous tissue after local BiTox injection. However, we found no evidence that BiTox was transported to the dorsal root ganglia or dorsal horn and no deficits in formalin-elicited behaviors or capsaicin or formalin-induced c-Fos expression within the dorsal horn. In contrast, Bitox treatment strongly reduced A-nociceptor-mediated secondary mechanical hyperalgesia associated with either complete Freund’s adjuvant (CFA)-induced joint inflammation or capsaicin injection and the hypersensitivity associated with spared nerve injury. These results imply that although local release of neuromodulators from C-fibers was inhibited by BiTox injection, C-nociceptive signaling function was not impaired. Taken together with recent clinical data the results suggest that BiTox should be considered for treatment of pain conditions in which A-nociceptors are thought to play a significant role.

Abobotulinum Toxin A in the Treatment of Chronic Low Back Pain

Chronic low back pain is a debilitating condition with a complex and multifactorial pathophysiology. Botulinum neurotoxins (BoNTs) have strong analgesic effects, as shown in both animal models of pain and in human beings. A randomized, double-blind, placebo-controlled, parallel format study to investigate the efficacy of abobotulinum toxin A (aboA) in chronic low back pain was conducted. The study cohort consisted of 18 patients who received 100 units of aboA into each of the five lumbar extensor spinae muscles unilaterally or bilaterally (total dose 500 to 1000 units), and 19 who received normal saline of the same volume. The level of pain and quality of life were assessed using the visual analogue scale (VAS) and three questionnaires including the Oswestry Low Back Pain Disability Questionnaire (OLBPDQ). Patients’ perception of improvement was recorded via patient global impression of change (PGIC). The primary outcome measure, the proportion of responders with VAS of <4 at 6 weeks, was not met, but the data was significantly in favor of aboA at 4 weeks (p = 0.008). The total Oswestry score representing quality of life improved in the aboA group compared to the placebo group (p = 0.0448). Moreover, significantly more patients reported their low back pain as “much improved” in the abobotulinum toxin A group (0.0293).

Chronic Migraine: An Update on Physiology, Imaging, and the Mechanism of Action of Two Available Pharmacologic Therapies

Several lines of research support the hypothesis that migraine is a spectrum of illness, with clinical symptoms that vary along a continuum from episodic migraine to chronic migraine. Physiologic changes may result in episodic migraine evolving into chronic migraine over months to years in susceptible individuals. With chronification, headache frequency increases, becoming more disabling and less responsive to therapy. Neurophysiologic and functional imaging research has reported that chronic migraine may be associated with severity‐specific metabolic, functional, and structural abnormalities in the brainstem. Without longitudinal studies, it is unclear whether these changes may represent a continuum of individual progression and/or are reversible. Furthermore, chronic migraine is associated with larger impairments in cortical processing of sensory stimuli when compared with episodic migraine, possibly caused by more pronounced cortical hyperexcitability.

Progressive changes in nociceptive thresholds and subsequent central sensitization due to recurrent migraine attacks in vulnerable individuals contribute to the chronic migraine state. This may result in changes to baseline neurologic function between headache attacks, evident in both electrophysiological and functional imaging research. Patients experiencing migraine chronification may report increased non‐headache pain, fatigue, psychiatric disorders (eg, depression, anxiety), gastrointestinal complaints, and other somatic conditions associated with their long‐term experience with migraine pain.

Recent research provides a foundation for differentiating episodic and chronic migraine based on neurophysiologic and neuroimaging tools. In this literature review, we consider these findings in the context of models designed to explain the physiology and progression of episodic migraine into chronic migraine, and consider treatment of chronic migraine in susceptible individuals. Advances in pharmacotherapy provide treatment options for chronic migraine. Of the currently available treatment options, only onabotulinumtoxinA and topiramate have received regulatory approval and have demonstrated efficacy in patients with chronic migraine, although the exact mechanisms of action are not fully elucidated.