Dural neurogenic inflammation induced by neuropathic pain is specific to cranial region

Neuromodulatory effects of leukotriene receptor antagonists: A comprehensive review

Cysteinyl leukotrienes (CysLTs) are central to the pathophysiology of asthma and various inflammatory disorders. Leukotriene receptor antagonists (LTRAs) effectively treat respiratory conditions by targeting cysteinyl leukotriene receptors, CysLT1 and CysLT2 subtypes. This review explores the multifaceted effects of LTs, extending beyond bronchoconstriction. CysLT receptors are not only present in the respiratory system but are also crucial in neuronal signaling pathways. LTRAs modulate these receptors, influencing downstream signaling, calcium levels, inflammation, and oxidative stress (OS) within neurons hinting at broader implications. Recent studies identify novel molecular targets, sparking interest in repurposing LTRAs for therapeutic use. Clinical trials are investigating their potential in neuroinflammation control, particularly in Alzheimer's disease (AD) and Parkinson's diseases (PD). However, montelukast, a long-standing LTRA since 1998, raises concerns due to neuropsychiatric adverse drug reactions (ADRs). Despite widespread use, understanding montelukast's metabolism and underlying ADR mechanisms remains limited. This review comprehensively examines LTRAs' diverse biological effects, emphasizing non-bronchoconstrictive activities. It also analyses plausible mechanisms behind LTRAs' neuronal effects, offering insights into their potential as neurodegenerative disease modulators. The aim is to inform clinicians, researchers, and pharmaceutical developers about LTRAs' expanding roles, particularly in neuroinflammation control and their promising repurposing for neurodegenerative disease management.

Peripheral and central neurobiological effects of botulinum toxin A (BoNT/A) in neuropathic pain: a systematic review

ABSTRACT

Botulinum toxin (BoNT), a presynaptic inhibitor of acetylcholine (Ach) release at the neuromuscular junction (NMJ), is a successful and safe drug for the treatment of several neurological disorders. However, a wide and recent literature review has demonstrated that BoNT exerts its effects not only at the "periphery" but also within the central nervous system (CNS). Studies from animal models, in fact, have shown a retrograde transport to the CNS, thus modulating synaptic function. The increasing number of articles reporting efficacy of BoNT on chronic neuropathic pain (CNP), a complex disease of the CNS, demonstrates that the central mechanisms of BoNT are far from being completely elucidated. In this new light, BoNT might interfere with the activity of spinal, brain stem, and cortical circuitry, modulating excitability and the functional organization of CNS in healthy conditions. Botulinum toxins efficacy on CNP is the result of a wide and complex action on many and diverse mechanisms at the basis of the maladaptive plasticity, the core of the pathogenesis of CNP. This systematic review aims to discuss in detail the BoNT's mechanisms and effects on peripheral and central neuroplasticity, at the basis for the clinical efficacy in CNP syndromes.

Nerve blocks for occipital headaches: A systematic review and meta-analysis

Migraine surgeons have identified six "trigger sites" where cranial nerve compression may trigger a migraine. This study investigates the change in headache severity and frequency following nerve block of the occipital trigger site. This PRISMA-compliant systematic review of five databases searched from database inception through May 2020 is registered under the PROSPERO ID: CRD42020199369. Only randomized controlled trials utilizing injection treatments for headaches with pain or tenderness in the occipital scalp were included. Pain severity was scored from 0 to 10. Headache frequency was reported as days per week. Included were 12 RCTs treating 586 patients of mean ages ranging from 33.7 to 55.8 years. Meta-analyses of pain severity comparing nerve blocks to baseline showed statistically significant reductions of 2.88 points at 5 to 20 min, 3.74 points at 1 to 6 weeks, and 1.07 points at 12 to 24 weeks. Meta-analyses of pain severity of nerve blocks compared with treatment groups of neurolysis, pulsed radiofrequency, and botulinum toxin type A showed similar headache pain severity at 1 to 2 weeks, and inferior improvements compared with the treatment groups after 2 weeks. Meta-analyses of headache frequency showed statistically significant reductions at 1 to 6-week follow-ups as compared with baseline and at 1 to 6 weeks as compared with inactive control injections. The severity and frequency of occipital headaches are reduced following occipital nerve blocks. This improvement is used to predict the success of migraine surgery. Future research should investigate spinous process injections with longer follow-up.

Chronic craniomandibular pain after craniotomy: A long-term clinical study

OBJECTIVE

Chronic craniomandibular/cervical pain and temporomandibular disorders have not been studied in patients who had a craniotomy several years previously. The aim of the current clinical work was to address these issues.

METHODS

A total group of 150 ambulant patients who had a previous craniotomy was subclassified according to whether or not the temporalis muscle was manipulated.

RESULTS

The average incidence of multiple subsite regional head and neck pain was 69.3% a number of years after a craniotomy. Evidence of internal derangement of the temporomandibular joint was significantly higher in the group that required manipulation of the temporalis muscle during the procedure.

CONCLUSION

The pattern of chronic craniomandibular/cervical pain experienced years after a craniotomy supports the brain neuromatrix theory of pain.

Outcomes of transcutaneous nerve stimulation for migraine headaches: a systematic review and meta-analysis

BACKGROUND

Implanted and transcutaneous nerve stimulators have shown promise as novel non-pharmacologic treatment for episodic and chronic migraines. The purpose of this study was to summarize the reported efficacy of transcutaneous single nerve stimulators in management of migraine frequency and severity.

METHODS

A systematic review of five databases identified studies treating migraines with transcutaneous stimulation of a single nerve. Random effects model meta-analyses were conducted to establish the effect of preventive transcutaneous nerve stimulation on headache days per month and 0-10 numeric rating scale pain severity of headaches for both individuals with episodic and chronic migraines.

RESULTS

Fourteen studies, which treated 995 patients, met inclusion criteria, including 7 randomized controlled trials and 7 uncontrolled clinical trials. Transcutaneous nerve stimulators reduced headache frequency in episodic migraines (2.81 fewer headache days per month, 95% CI 2.18-3.43, I² = 21%) and chronic migraines (2.97 fewer headache days per month, 95% CI 1.66-4.28, I² = 0%). Transcutaneous nerve stimulators reduced headache severity in episodic headaches (2.23 fewer pain scale points, 95% CI 1.64-2.81, I² = 88%).

CONCLUSIONS

Preventive use of transcutaneous nerve stimulators provided clinically significant reductions in headache frequency in individuals with chronic or episodic migraines. Individuals with episodic migraines also experienced a reduction in headache pain severity following preventive transcutaneous nerve stimulation.

Association of Intranasal and Neurogenic Dural Inflammation in Experimental Acute Rhinosinusitis

Background

Nasal cavity and sinus disorders, such as allergic rhinitis, rhinosinusitis, or certain anatomical defects, are often associated with transient or ongoing headaches. On the other hand, migraine headache patients often exhibit pain referral over the area of nasal sinuses and typical nasal autonomic symptoms involving congestion and rhinorrhea. Mechanism for convergence of nasal or sinus disorders and headaches is unknown. Herein, we examined the association of sino-nasal inflammatory pain with common preclinical indicators of trigeminovascular system activation such as dural neurogenic inflammation (DNI) and neuronal activation in brainstem nociceptive nuclei.

Methods

Nasal and paranasal cavity inflammation and pain was induced by formalin (2.5%/10 μl) or capsaicin (0.1%/10 μl) instillation at the border of maxillary sinus and nasal cavity in rats. Quantification of inflammation of nasal mucosa and DNI was performed by spectrophotometric measurement of Evans blue - plasma protein complex extravasation. Pain behavior was quantified by rat grimace scale (RGS). Nociceptive neuronal activation in caudal part of spinal trigeminal nucleus (TNC) was assessed by c-Fos protein immunohistochemistry.

Results

Capsaicin and formalin administered into rat nasal cavity increased plasma protein extravasation in the nasal mucosa and dura mater. Intensity of plasma protein extravasation in nasal mucosa correlated with extravasation in dura. Similarly, facial pain intensity correlated with nociceptive neuronal c-Fos activation in the TNC.

Conclusion

Present data show that inflammatory stimuli in deep nasal and paranasal structures provoke distant intracranial changes related to trigeminovascular system activation. We hypothesize that this phenomenon could explain overlapping symptoms and comorbidity of nasal/paranasal inflammatory disorders with migraine.

New analgesic: Focus on botulinum toxin

In 2010, Kissin concluded pessimistically that of the 59 new drugs introduced in the fifty-year period between 1960 and 2009 and still in use, only seven had new molecular targets. Of these, only one, sumatriptan, was effective enough to lead to the introduction of multiple drugs targeting the same target molecules (triptans) (Kissin, 2010). Morphine and acetylsalicylic acid (aspirin), introduced for the treatment of pain more than a century ago, continue to dominate biomedical publications despite their limited effectiveness in many areas (e.g., neuropathic pain) and serious adverse effects. Today, are we really closer to ideal analgesics that would work hard enough, long enough, and did not have unwanted side effects? The purpose of the present article is to analyze where we are now. Several drugs, like long-acting opioids or botulinum toxins open some hope. Advantage of botulinum toxin A is unique duration of action (months). New discoveries showed that after peripheral application botulinum toxin by axonal transport reaches the CNS. Major analgesic mechanism of action seems to be of central origin. Will botulinum toxin in the CNS bring new indications and or/adverse effects? Much more basic and clinical research should be in front of us. Although relatively safe as a drug, botulinum toxin is not without adverse effect. Policy makers, clinicians and all those applying botulinum toxin should be aware of that. Unfortunately the life without the pain is still not possible.

Botulinum Toxin and Pain

This chapter is focused on analgesic mechanism of action of botulinum toxin type A (BoNT-A) including the action beyond peripheral nerve endings. With the exception of the meninges and possibly urinary bladder, the presence of BoNT-A activity in the periphery, cleaving SNAP25 as a target molecule, up to now was not convincingly shown. In contrast many reports demonstrated BoNT-A activity and the presence of cleaved SNAP25 in the brain and spinal cord. In a model of mirror pain BoNT-A analgesic effect can be achieved even without participation of peripheral nerve ending. Thus generalized hypothesis central or peripheral mechanism of action belongs to history, and there is a need to confirm or dispute the results with meninges, urinary bladder, and possibly with other, especially visceral organs.There are two general options for the central actions of BoNT-A: 1. The activity ends by silencing primary sensory neuron thereby stopping the pain information further in the CNS. 2. Or thereafter, indirectly or transsynaptically, BoNT-A triggers smaller or larger neural loops, forming memory of pain in the CNS that could explain the bilateral effects after unilateral peripheral administration, similar effect in mirror image allodynia and the like Intensive research has shown that peripherally administered BoNT-A reaches the CNS by axonal transport. There is increasing evidence that BoNT-A is preventing pain in a growing range of disorders. In the absence of unexpected findings, or an increase in the uncontrolled use of illicit preparations by uneducated persons, BoNT-A is emerging as a new long-lasting and relatively safe analgesic.

Treatment of Frontal Secondary Headache Attributed to Supratrochlear and Supraorbital Nerve Entrapment With Oral Medication or Botulinum Toxin Type A vs Endoscopic Decompression Surgery

Importance

Endoscopic surgical decompression of the supratrochlear nerve (STN) and supraorbital nerve (SON) is a new treatment for patients with frontal chronic headache who are refractory to standard treatment options.

Objective

To evaluate and compare treatment outcomes of oral medication, botulinum toxin type A (BoNT/A) injections, and endoscopic decompression surgery in frontal secondary headache attributed to STN and supraorbital SON entrapment.

Design, Setting, and Participants

Prospective cohort study of 22 patients from a single institution (Diakonessen Hospital Utrecht) with frontal headache of moderate-to-severe intensity (visual analog scale [VAS] score, 7-10), frontally located, experienced more than 15 days per month, and described as pressure or tension that intensifies with pressure on the area of STN and SON. A screening algorithm was used that included examination, questionnaire, computed tomography of the sinus, injections of local anesthetic, and BoNT/A in the corrugator muscle.

Interventions

Different oral medication therapy for headache encountered in the study cohort, as well as BoNT/A injections (15 IU) into the corrugator muscle. Surgical procedures were performed by a single surgeon using an endoscopic surgical approach to release the supraorbital ridge periosteum and to bluntly dissect the glabellar muscle group.

Main Outcomes and Measures

Headache VAS intensity after oral medication and BoNT/A injections. Additionally, early postoperative follow-up consisted of a daily headache questionnaire that was evaluated after 1 year.

Results

In total, 22 patients (mean [SD] age, 42.0 [15.3] years; 7 men and 15 women) were included in this cohort study. Oral medication therapy reduced the headache intensity significantly (mean [standard error of the mean {SEM}] VAS score, 6.45 [0.20] [95% CI, 0.34-3.02; P < .001] compared with mean [SEM] pretreatment VAS score, 8.13 [0.22]). Botulinum toxin type A decreased the mean (SEM) headache intensity VAS scores significantly as well (pretreatment, 8.1 [0.22] vs posttreatment, 2.9 [0.42]; 95% CI, 3.89-6.56; P < .001). The mean (SEM) pretreatment headache intensity VAS score (8.10 [0.22]) decreased significantly after surgery at 3 months (1.30 [0.55]; 95% CI, 5.48-8.16; P < .001) and 12 months (1.09 [0.50]; 95% CI, 5.71-8.38; P < .001). There was a significant decrease of headache intensity VAS score in the surgical group over the BoNT/A group (mean [SEM] VAS score, 2.90 [0.42]) after 3 months (mean [SEM] VAS score, 1.30 [0.55]; 95% CI, 0.25-2.93; P < .001) and 12 months (mean [SEM] VAS score, 1.09 [0.50]; 95% CI, 0.48-3.16; P < .001) after surgery.

Conclusions and Relevance

Endoscopic decompression surgery had a long-lasting successful outcome in this type of frontal secondary headache. Even though BoNT/A had a positive effect, the effect of surgery was significantly higher.

Level of Evidence

3.

Entrapment Neuropathy: A Concept for Pathogenesis and Treatment of Headaches-A Narrative Review

Entrapment neuropathy is a known cause of neurological disorders. In the head and neck area, this pathophysiological mechanism could be a trigger for headache. Over the last few decades, injection of botulinum toxin type A in the muscles that are causing the compression as well as surgical decompression have proved to be effective treatment methods worldwide for large numbers of patients with daily headaches. In particular the entrapment of the supraorbital nerves in the glabellar musculature and the occipital nerves in the neck musculature are triggers for headache disorders for which many patients are still seeking an effective treatment. This article reviews the literature and aims to bring the concept of neural entrapment to the attention of a wider audience. By doing so, we hope to give more exposure to an effective and relatively safe headache treatment.

Preliminary Study on the Relationship Between Inflammation and Hemifacial Spasm

BACKGROUND

Complete pathogenesis of hemifacial spasm (HFS) is unknown. In some patients with HFS, thickened, opaque, and sticky arachnoid membranes have been found during microvascular decompression procedures. This phenomenon indicates a possible relationship between inflammation and HFS. The aim of this study was to explore the role of inflammation in pathogenesis of HFS.

METHODS

Levels of interferon-γ, interleukin-2 receptor, interleukin-6 (IL-6), interleukin-8, interleukin-10, and tumor necrosis factor α and white blood cell (WBC), neutrophil, and lymphocyte counts were compared between patients with HFS, patients with lumbar disc herniation, and healthy control subjects. A receiver operating characteristic curve analysis was performed to evaluate the diagnostic significance of peripheral blood inflammatory markers for HFS. All the inflammatory markers were further analyzed by single and multiple logistic regression analysis.

RESULTS

Patients with HFS had greater IL-6, interleukin-8, white blood cell count, and neutrophil count than patients with lumbar disc herniation and healthy control subjects. Area under curve values of IL-6, white blood cell count, and neutrophil count were >0.8. Multiple logistic regression analysis indicated that only interleukin-2 receptor and IL-6 were relevant to HFS.

CONCLUSIONS

Inflammation is relative to HFS. IL-6 may be 1 of many factors involved in pathogenesis of HFS.

A novel large animal model of recurrent migraine established by repeated administration of inflammatory soup into the dura mater of the rhesus monkey

Several animal models of migraine have been established, and those based on trigeminovascular system activation are widely accepted. However, most of these models have been established on lower animals, such as rodents, and involve only a single administration of a noxious stimulus. In this study, an inflammatory soup (10 μL), consisting of prostaglandin E2 (0.2 mM), serotonin (2 mM), bradykinin (2 mM) and histamine (2 mM), was injected into the dura mater of conscious rhesus monkeys through an indwelling catheter. The infusion started on day 8 and was repeated every 3 days, for a total of six administrations, to induce neurogenic inflammation. We performed behavioral assessments and measured the expression of the oncogene c-fos, neuronal nitric oxide synthase (nNOS) and calcitonin gene related peptide (CGRP) in the trigeminal system and in multiple brain regions involved in pain processing by immunohistochemical staining. Compared with monkeys in the control group, three of the four animals in the inflammatory soup group displayed decreased motor behaviors, and two showed increased ipsilateral nose and mouth secretions during the stimulus period. Higher expression levels of c-fos, nNOS and CGRP were found in various brain areas of experimental animals compared with controls, including the trigeminal nucleus caudalis, thalamus, hypothalamus, midbrain, pons and other areas involved in pain perception. These results suggest that repeated inflammatory soup stimulation of the dura activates the trigeminovascular system and produces migraine-like pathological changes and abnormal behaviors in conscious rhesus monkeys.

Activity of botulinum toxin type A in cranial dura: implications for treatment of migraine and other headaches

BACKGROUND AND PURPOSE

Although botulinum toxin type A (BoNT/A) is approved for chronic migraine treatment, its mechanism of action is still unknown. Dural neurogenic inflammation (DNI) commonly used to investigate migraine pathophysiology can be evoked by trigeminal pain. Here, we investigated the reactivity of cranial dura to trigeminal pain and the mechanism of BoNT/A action on DNI.

EXPERIMENTAL APPROACH

Because temporomandibular disorders are highly comorbid with migraine, we employed a rat model of inflammation induced by complete Freund's adjuvant, followed by treatment with BoNT/A injections or sumatriptan p.o. DNI was assessed by Evans blue-plasma protein extravasation, cell histology and RIA for CGRP. BoNT/A enzymatic activity in dura was assessed by immunohistochemistry for cleaved synaptosomal-associated protein 25 (SNAP-25).

KEY RESULTS

BoNT/A and sumatriptan reduced the mechanical allodynia and DNI, evoked by complete Freund's adjuvant. BoNT/A prevented inflammatory cell infiltration and inhibited the increase of CGRP levels in dura. After peripheral application, BoNT/A-cleaved SNAP-25 colocalized with CGRP in intracranial dural nerve endings. Injection of the axonal transport blocker colchicine into the trigeminal ganglion prevented the formation of cleaved SNAP-25 in dura.

CONCLUSIONS AND IMPLICATIONS

Pericranially injected BoNT/A was taken up by local sensory nerve endings, axonally transported to the trigeminal ganglion and transcytosed to dural afferents. Colocalization of cleaved SNAP-25 and the migraine mediator CGRP in dura suggests that BoNT/A may prevent DNI by suppressing transmission by CGRP. This might explain the effects of BoNT/A in temporomandibular joint inflammation and in migraine and some other headaches.

Fathoming the kynurenine pathway in migraine: why understanding the enzymatic cascades is still critically important

Kynurenine pathway, the quantitatively main branch of tryptophan metabolism, has been long been considered a source of nicotinamide adenine dinucleotide, although several of its products, the so-called kynurenines, are endowed with the capacity to activate glutamate receptors, thus potentially influencing a large group of functions in the central nervous system (CNS). Migraine, a largely unknown pathology, is strictly related to the glutamate system in the CNS pathologic terms. Despite the large number of studies conducted on migraine etio-pathology, the kynurenine pathway has been only recently linked to this disease. Nonetheless, some evidence suggests an intriguing role for some kynurenines, and an exploratory study on the serum kynurenine level might be helpful to better understand possible alterations of the kynurenine pathway in patients suffering from migraine.

Botulinum toxin A, brain and pain

Botulinum neurotoxin type A (BoNT/A) is one of the most potent toxins known and a potential biological threat. At the same time, it is among the most widely used therapeutic proteins used yearly by millions of people, especially for cosmetic purposes. Currently, its clinical use in certain types of pain is increasing, and its long-term duration of effects represents a special clinical value. Efficacy of BoNT/A in different types of pain has been found in numerous clinical trials and case reports, as well as in animal pain models. However, sites and mechanisms of BoNT/A actions involved in nociception are a matter of controversy. In analogy with well known neuroparalytic effects in peripheral cholinergic synapses, presently dominant opinion is that BoNT/A exerts pain reduction by inhibiting peripheral neurotransmitter/inflammatory mediator release from sensory nerves. On the other hand, growing number of behavioral and immunohistochemical studies demonstrated the requirement of axonal transport for BoNT/A's antinociceptive action. In addition, toxin's enzymatic activity in central sensory regions was clearly identified after its peripheral application. Apart from general pharmacology, this review summarizes the clinical and experimental evidence for BoNT/A antinociceptive activity and compares the data in favor of peripheral vs. central site and mechanism of action. Based on literature review and published results from our laboratory we propose that the hypothesis of peripheral site of BoNT/A action is not sufficient to explain the experimental data collected up to now.