A fMRI evaluation of lamotrigine for the treatment of trigeminal neuropathic pain: pilot study

Connexin 36 Mediates Orofacial Pain Hypersensitivity Through GluK2 and TRPA1

Trigeminal neuralgia is a debilitating condition, and the pain easily spreads to other parts of the face. Here, we established a mouse model of partial transection of the infraorbital nerve (pT-ION) and found that the Connexin 36 (Cx36) inhibitor mefloquine caused greater alleviation of pT-ION-induced cold allodynia compared to the reduction of mechanical allodynia. Mefloquine reversed the pT-ION-induced upregulation of Cx36, glutamate receptor ionotropic kainate 2 (GluK2), transient receptor potential ankyrin 1 (TRPA1), and phosphorylated extracellular signal regulated kinase (p-ERK) in the trigeminal ganglion. Cold allodynia but not mechanical allodynia induced by pT-ION or by virus-mediated overexpression of Cx36 in the trigeminal ganglion was reversed by the GluK2 antagonist NS102, and knocking down Cx36 expression in Nav1.8-expressing nociceptors by injecting virus into the orofacial skin area of Nav1.8-Cre mice attenuated cold allodynia but not mechanical allodynia. In conclusion, we show that Cx36 contributes greatly to the development of orofacial pain hypersensitivity through GluK2, TRPA1, and p-ERK signaling.

Neuromodulators for Atypical Facial Pain and Neuralgias: A Systematic Review and Meta-Analysis

OBJECTIVE

To evaluate the effectiveness of neuromodulating agents for the management of atypical facial pain and primary facial neuralgias.

METHODS

We searched MEDLINE, Embase, CINAHL, and ClinicalTrials.gov databases for original research articles that examine the effectiveness and adverse reactions of pharmacologic therapy for the treatment of trigeminal neuralgia and atypical facial pain. Studies that included surgical interventions for atypical facial pain or facial pain secondary to other causes were excluded. Meta-analysis was conducted for reductions in symptom scores and adverse effects.

RESULTS

Of 3,409 articles screened, 73 full-text articles were included, consisting of 45 observational studies and 29 randomized controlled trials. Twenty-four different pharmacological agents were assessed; carbamazepine was the most frequently studied while botulinum toxin A demonstrated the highest consistency in reduction of symptom scores. Pooled estimate of three randomized controlled trials revealed that patients with trigeminal neuralgia who received botulinum toxin A had higher odds (odds ratio 7.46; 95% CI 3.53-15.78) of achieving a ≥50% reduction in visual analogue scale scores compared to controls. Pooled estimate of 15 observational studies showed that three-fourths of patients with trigeminal neuralgia who received carbamazepine experienced clinically significant pain reduction (prevalence proportion 0.75; 95% CI 0.66-0.83).

CONCLUSIONS

Patients receiving botulinum toxin A for trigeminal neuralgia had higher odds of achieving ≥50% reduction in pain scores. A significant proportion of patients with trigeminal neuralgia experienced positive response to carbamazepine. There was moderate evidence for amitriptyline in patients with atypical facial pain. Standardization of outcome reporting would facilitate future quantitative comparisons of therapeutic effectiveness. Laryngoscope, 131:1235-1253, 2021.

Targeting migraine treatment with neuroimaging-Pharmacological neuroimaging in headaches

PURPOSE

The current review provides a recapitulation of recent advances in pharmacological neuroimaging in headache, a promising tool to understanding of how a drug works in the brain and how it may lead to new insights of disease mechanisms of headache.

RESULTS

Pharmacological positron emission tomography with radioligand-labeled medication may provide evidence whether and where a medication binds in the brain but is still mostly restricted to animal work. Pharmacological functional MRI using task-specific approaches identified central modulation patterns as a consequence of attack and preventative headache medication, which may be distinct to a specific drug mechanism. Pharmacological neuroimaging and specifically in combination with functional imaging is a promising tool to better understand not only certain medications but also certain disease mechanisms.

SUMMARY

Pharmacological imaging techniques have advanced over the last few years and showed great potential of providing new insights into drug pharmacodynamics and disease mechanism. There are still limitations and challenges to be overcome.

Altered structure and functional connection in patients with classical trigeminal neuralgia

Classical trigeminal neuralgia (TN) is a specific type of neuropathic orofacial pain of which the plasticity of brain structure and connectivity have remained largely unknown. A total of 62 TN patients were included and referred to MRI scans. Voxel-based morphometry was used to analyze the change of gray matter volume. Resting-state functional imaging was used to analyze the connectivity between brain regions. The results showed gray matter volume reduction in components of the prefrontal cortex, precentral gyrus, cerebellar tonsil, thalamus, hypothalamus, and nucleus accumbens among right TN patient and in the inferior frontal gyrus, precentral gyrus, cerebellum, thalamus, ventral striatum, and putamen among left TN patients. The connections between the right superior frontal gyrus and right middle frontal gyrus were lower in right TN patients. The connection between the left precentral gyrus and the left superior frontal gyrus was lower while the connection between bilateral thalamus was higher in left TN patients. The changes of volume in bilateral thalamus of right TN patients and left ventral striatum of left TN patients, and the connectivity between bilateral thalamus of left TN patients were moderately correlated with pain duration. These findings suggest that brain regions such as the thalamus may not only be involved in processing of pain stimuli but also be important for the development of TN. The left hemisphere may be dominant in processing and modulation of TN pain signal. Chronification of TN induces volume changes in brain regions which are associated with emotional or cognitive modulation of pain. Hum Brain Mapp 39:609-621, 2018. © 2017 Wiley Periodicals, Inc.

A critical evaluation of validity and utility of translational imaging in pain and analgesia: Utilizing functional imaging to enhance the process

Assessing clinical pain and metrics related to function or quality of life predominantly relies on patient reported subjective measures. These outcome measures are generally not applicable to the preclinical setting where early signs pointing to analgesic value of a therapy are sought, thus introducing difficulties in animal to human translation in pain research. Evaluating brain function in patients and respective animal model(s) has the potential to characterize mechanisms associated with pain or pain-related phenotypes and thereby provide a means of laboratory to clinic translation. This review summarizes the progress made towards understanding of brain function in clinical and preclinical pain states elucidated using an imaging approach as well as the current level of validity of translational pain imaging. We hypothesize that neuroimaging can describe the central representation of pain or pain phenotypes and yields a basis for the development and selection of clinically relevant animal assays. This approach may increase the probability of finding meaningful new analgesics that can help satisfy the significant unmet medical needs of patients.

The enigma of site of action of migraine preventives: no effect of metoprolol on trigeminal pain processing in patients and healthy controls

Background

Beta-blockers are a first choice migraine preventive medication. So far it is unknown how they exert their therapeutic effect in migraine. To this end we examined the neural effect of metoprolol on trigeminal pain processing in 19 migraine patients and 26 healthy controls. All participants underwent functional magnetic resonance imaging (fMRI) during trigeminal pain twice: Healthy subjects took part in a placebo-controlled, randomized and double-blind study, receiving a single dose of metoprolol and placebo. Patients were examined with a baseline scan before starting the preventive medication and 3 months later whilst treated with metoprolol.

Results

Mean pain intensity ratings were not significantly altered under metoprolol. Functional imaging revealed no significant differences in nociceptive processing in both groups. Contrary to earlier findings from animal studies, we did not find an effect of metoprolol on the thalamus in either group. However, using a more liberal and exploratory threshold, hypothalamic activity was slightly increased under metoprolol in patients and migraineurs.

Conclusions

No significant effect of metoprolol on trigeminal pain processing was observed, suggesting a peripheral effect of metoprolol. Exploratory analyses revealed slightly enhanced hypothalamic activity under metoprolol in both groups. Given the emerging role of the hypothalamus in migraine attack generation, these data need further examination.

The usefulness of diagnostic imaging for the assessment of pain symptoms in temporomandibular disorders

The causes of pain symptoms in the temporomandibular joint (TMJ) and masticatory muscle (MM) regions may not be determined by clinical examination alone. In this review, we document that pain symptoms of the TMJ and MM regions in patients with temporomandibular disorders (TMDs) are associated with computed tomography and magnetic resonance (MR) findings of internal derangement, joint effusion, osteoarthritis, and bone marrow edema. However, it is emphasized that these imaging findings must not be regarded as the unique and dominant factors in defining TMJ pain. High signal intensity and prominent enhancement of the posterior disk attachment on fat saturation T2-weighted imaging and dynamic MR imaging with contrast material are closely correlated with the severity of TMJ pain. Magnetic transfer contrast, MR spectroscopy, diffusion tensor imaging, and ultrasonography findings have helped identify intramuscular edema and contracture as one of the causes of MM pain and fatigue. Recently, changes in brain as detected by functional MR neuroimaging have been associated with changes in the TMJ and MM regions. The thalamus, the primary somatosensory cortex, the insula, and the anterior and mid-cinglate cortices are most frequently associated with TMD pain.

Distinct BOLD fMRI Responses of Capsaicin-Induced Thermal Sensation Reveal Pain-Related Brain Activation in Nonhuman Primates

Background

Approximately 20% of the adult population suffer from chronic pain that is not adequately treated by current therapies, highlighting a great need for improved treatment options. To develop effective analgesics, experimental human and animal models of pain are critical. Topically/intra-dermally applied capsaicin induces hyperalgesia and allodynia to thermal and tactile stimuli that mimics chronic pain and is a useful translation from preclinical research to clinical investigation. Many behavioral and self-report studies of pain have exploited the use of the capsaicin pain model, but objective biomarker correlates of the capsaicin augmented nociceptive response in nonhuman primates remains to be explored.

Methodology

Here we establish an aversive capsaicin-induced fMRI model using non-noxious heat stimuli in Cynomolgus monkeys (n = 8). BOLD fMRI data were collected during thermal challenge (ON:20 s/42°C; OFF:40 s/35°C, 4-cycle) at baseline and 30 min post-capsaicin (0.1 mg, topical, forearm) application. Tail withdrawal behavioral studies were also conducted in the same animals using 42°C or 48°C water bath pre- and post- capsaicin application (0.1 mg, subcutaneous, tail).

Principal Findings

Group comparisons between pre- and post-capsaicin application revealed significant BOLD signal increases in brain regions associated with the ‘pain matrix’, including somatosensory, frontal, and cingulate cortices, as well as the cerebellum (paired t-test, p<0.02, n = 8), while no significant change was found after the vehicle application. The tail withdrawal behavioral study demonstrated a significant main effect of temperature and a trend towards capsaicin induced reduction of latency at both temperatures.

Conclusions

These findings provide insights into the specific brain regions involved with aversive, ‘pain-like’, responses in a nonhuman primate model. Future studies may employ both behavioral and fMRI measures as translational biomarkers to gain deeper understanding of pain processing and evaluate the preclinical efficacy of novel analgesics.

Pharmacologic modulation of hand pain in osteoarthritis: a double-blind placebo-controlled functional magnetic resonance imaging study using naproxen

OBJECTIVE

In an attempt to shed light on management of chronic pain conditions, there has long been a desire to complement behavioral measures of pain perception with measures of underlying brain mechanisms. Using functional magnetic resonance imaging (fMRI), we undertook this study to investigate changes in brain activity following the administration of naproxen or placebo in patients with pain related to osteoarthritis (OA) of the carpometacarpal (CMC) joint.

METHODS

A placebo-controlled, double-blind, 2-period crossover study was performed in 19 individuals with painful OA of the CMC joint of the right hand. Following placebo or naproxen treatment periods, a functionally relevant task was performed, and behavioral measures of the pain experience were collected in identical fMRI examinations. Voxelwise and a priori region of interest analyses were performed to detect between-period differences in brain activity.

RESULTS

Significant reductions in brain activity following treatment with naproxen, compared to placebo, were observed in brain regions commonly associated with pain perception, including the bilateral primary somatosensory cortex, thalamus, and amygdala. Significant relationships between changes in perceived pain intensity and changes in brain activity were also observed in brain regions previously associated with pain intensity.

CONCLUSION

This study demonstrates the sensitivity of fMRI to detect the mechanisms underlying treatments of known efficacy. The data illustrate the enticing potential of fMRI as an adjunct to self-report for detecting early signals of efficacy of novel therapies, both pharmacologic and nonpharmacologic, in small numbers of individuals with persistent pain.

A new electronic diary tool for mapping and tracking spatial and temporal head pain patterns in migraine

AIM

We present an electronic tool for collecting data on the patterns of migraine headache onset and progression.

METHODS

A digitized map consisting of 44 color-coded segments was defined based on previous reports of migraine pain and the distribution of nerves in the face, head and neck. The map was overlaid on a schematic map of the face, head and neck nerves. Thirty-six patients (N = 36, 28 female/eight male), who met ICDH-II criteria for episodic migraine and had headaches for at least three years, identified all regions where pain typically started and how pain spread and subsequently progressed.

RESULTS

Consistent with previous findings, throbbing was the most prevalent quality of migraine pain, always present in 70% of patients surveyed. For the 70% of the patients with throbbing pain, the temple was the onset site of throbbing pain, with no significant difference in the laterality of onset site (58.3% on the right vs. 55.6% on the left hemisphere). The tool was able to capture patterns of pain distribution for throbbing and pressure headache pain and also may be used to assess the change in the pattern of the pain distribution as the disease progresses.

DISCUSSION

The pain map survey may be a useful tool for recording and tracking the temporal pattern of migraine onset both for clinical and research purposes. The tool could be used to create maps of pain locations on a large population scale and thus will be a very useful tool in correlating the temporal nature of headache symptoms with potential mechanisms of disease evolution.

Brain signature of chronic orofacial pain: a systematic review and meta-analysis on neuroimaging research of trigeminal neuropathic pain and temporomandibular joint disorders

Brain neuroimaging has been widely used to investigate the bran signature of chronic orofacial pain, including trigeminal neuropathic pain (TNP) and pain related to temporomandibular joint disorders (TMD). We here systematically reviewed the neuroimaging literature regarding the functional and structural changes in the brain of TNP and TMD pain patients, using a computerized search of journal articles via PubMed. Ten TNP studies and 14 TMD studies were reviewed. Study quality and risk of bias were assessed based on the criteria of patient selection, the history of medication, the use of standardized pain/psychological assessments, and the model and statistics of imaging analyses. Qualitative meta-analysis was performed by examining the brain regions which showed significant changes in either brain functions (including the blood-oxygen-level dependent signal, cerebral blood flow and the magnetic resonance spectroscopy signal) or brain structure (including gray matter and white matter anatomy). We hypothesized that the neuroimaging findings would display a common pattern as well as distinct patterns of brain signature in the disorders. This major hypothesis was supported by the following findings: (1) TNP and TMD patients showed consistent functional/structural changes in the thalamus and the primary somatosensory cortex, indicating the thalamocortical pathway as the major site of plasticity. (2) The TNP patients showed more alterations at the thalamocortical pathway, and the two disorders showed distinct patterns of thalamic and insular connectivity. Additionally, functional and structural changes were frequently reported in the prefrontal cortex and the basal ganglia, suggesting the role of cognitive modulation and reward processing in chronic orofacial pain. The findings highlight the potential for brain neuroimaging as an investigating tool for understanding chronic orofacial pain.

Pharmacological neuroimaging in headache and pain

PURPOSE OF REVIEW

The current review gives an overview about recent advances in neuroimaging studies with specific emphasis on pharmacological modulation of pain and headache. Further, we want to highlight how imaging methods have changed our understanding of chronic pain and discuss how pharmacological MRI could lead to new insights into underlying mechanisms of headache and pain.

RECENT FINDINGS

Several studies from different imaging laboratories have highlighted the outstanding role of imaging in getting a deeper insight regarding the central mechanisms of drugs. Neuroimaging techniques start to unravel how analgesic drugs, antidepressants or NSAIDs act on pain perception and in particular on central pain processes. Furthermore, the studies included in this review show how context dependent drugs act and how differently they reveal their action in the human brain.

SUMMARY

Imaging techniques give us the opportunity to gain a better understanding of drug processes in the central nervous system and help to understand where drugs reveal their therapeutic effect. While some substances work on the emotional-affective component of pain, others modulate sensory-discriminative pain pathways. Especially in the field of headache research, still a lot has to be done to understand how preventatives and acute medication modulate the human brain. Future studies should also replicate and extend recent findings.

Refractory trigeminal neuralgia. Non-surgical treatment options

The guidelines on trigeminal neuralgia management published by the American Academy of Neurology (AAN) and the European Federation of Neurological Societies (EFNS) recommended that patients unresponsive to carbamazepine or oxcarbazepine be offered the surgical option. However, because some patients may not be willing to resort to surgery, we searched the literature for treatment in refractory trigeminal neuralgia. We found other oral treatments, intranasal spray, subcutaneous injections, various kinds of peripheral nerve blocks and injections of botulinum toxin. On the basis of the available evidence we suggest that no oral treatment other than carbamazepine or oxcarbazepine is useful. Among the other options, there is increasingly strong evidence that botulinum toxin injections are efficacious and may be offered before surgery or to those unwilling to undergo surgery.

Cyclotraxin-B, a new TrkB antagonist, and glial blockade by propentofylline, equally prevent and reverse cold allodynia induced by BDNF or partial infraorbital nerve constriction in mice

Several lines of evidence indicate that brain-derived neurotrophic factor (BDNF) plays a key role as a central pronociceptive modulator of pain, acting through postsynaptic TrkB receptors that trigger intracellular signaling cascades leading to central sensitization. The overall aim of this study was to investigate to what extent BDNF could participate in the generation and maintenance of trigeminal neuropathic pain. The results showed that acute intracisternal administration of nanogram doses of BDNF in naïve mice elicited long-lasting, dose-related, cold allodynic responses to topical application of acetone onto vibrissal pad skin. The systemic administration of cyclotraxin-B (CTX-B), a new TrkB receptor antagonist, or propentofylline, an inhibitor of glial activation, was able to either prevent or reverse the effects of intracisternal BDNF on cold nociception. In addition, the blockade of TrkB receptor by CTX-B inhibited the mechanisms that either initiate or maintain cold allodynia in the ipsilateral vibrissal pad skin after unilateral constriction of the infraorbital nerve. These observations raise the possibility that BDNF is capable on its own of conveying many features of the signaling mechanisms that underlie central sensitization caused by nerve constriction.

PERSPECTIVE

Although further studies are necessary to examine in detail the mechanisms underlying the strong anti-allodynic action of CTX-B, this compound may represent an interesting lead for the development of novel therapeutic strategies aimed at preventing and/or suppressing central sensitization associated with neuropathic pain.