Trigeminofacial reflexes in primary headaches

The neurobiology of cluster headache

Cluster headache is a primary headache form occurring in paroxysmal excruciatingly severe unilateral head pain attacks usually grouped in periods lasting 1-2months, the cluster periods. A genetic component is suggested by the familial occurrence of the disease but a genetic linkage is yet to be identified. Contemporary activation of trigeminal and cranial parasympathetic systems-the so-called trigemino-parasympathetic reflex-during the headache attacks seem to cause the pain and accompanying oculo-facial autonomic phenomena respectively. At peripheral level, the increased calcitonin gene related peptide (CGRP) plasma levels suggests trigeminal system activation during cluster headache attacks. The temporal pattern of the disease both in terms of circadian rhythmicity and seasonal recurrence has suggested involvement of the hypothalamic biological clock in the pathophysiology of cluster headache. The posterior hypothalamus was investigate as the cluster generator leading to activation of the trigemino-parasympathetic reflex, but the accumulated experience after 20 years of hypothalamic electrical stimulation to treat the condition indicate that this brain region rather acts as pain modulator. Efficacy of monoclonal antibodies to treat episodic cluster headache points to a key role of CGRP in the pathophysiology of the condition.

Impairment of Inhibition of Trigeminal Nociception via Conditioned Pain Modulation in Persons with Migraine Headaches

OBJECTIVE

To assess conditioned pain modulation efficiency in persons with and without migraine headaches.

DESIGN

Cross-sectional assessment of experimental pain.

SETTING

University campus and surrounding community in a large Midwestern US city.

SUBJECTS

Twenty-three adults with and 32 without a history of migraine headaches participated in the study. Participants were mostly female (N = 40) with an average age of 23 years.

METHODS

Four electrocutaneous stimulations of the supraorbital branch of the left trigeminal nerve were delivered at 150% of an individually determined pain threshold. Conditioned pain modulation was assessed by applying a noxious counterstimulus (forearm ischemia) and delivering four more electrocutaneous stimulations. After each stimulation, pain and the nociceptive blink reflex were assessed. Depression and pain catastrophizing were assessed to control for the potential influence of these variables on pain modulation.

RESULTS

Participants with and without migraine headaches had similar baseline pain responsivity, without significant differences in pain report or nociceptive blink reflexes. Pain report was inhibited by conditioned pain modulation in both the migraine and control groups. However, unlike nonmigraine controls, participants with migraines did not exhibit an inhibition of nociceptive blink reflexes during the ischemia task. This pattern persisted after controlling for level of pain catastrophizing and depression.

CONCLUSIONS

Migraine sufferers exhibited impaired conditioned pain modulation of the nociceptive blink reflex, suggesting a deficiency in inhibition of trigeminal nociception, which may contribute to the development of migraine headaches.

The power features of Masseter muscle activity in tension-type and migraine without aura headache during open-close clench cycles

Introduction

Different types of headaches and TMJ click influence the masseter muscle activity. The aim of this study was to assess the trend of energy level of the electromyography (EMG) activity of the masseter muscle during open-close clench cycles in migraine without aura (MOA) and tension-type headache (TTH) with or without TMJ click.

Methods

Twenty-five women with MOA and twenty four women with TTH participated in the study. They matched with 25 healthy subjects, in terms of class of occlusion and prevalence of temporomandibular joint (TMJ) with click. The EMG of both masseter muscles were recorded during open-close clench cycles at a rate of 80 cycles per minute for 15 seconds. The mouth opening was restricted to two centimeters by mandibular motion frame. Signal processing steps have been done on the EMG as: noise removing, smoothing, feature extraction, and statistical analyzing. The six statistical parameters of energy computed were mean, Variance, Skewness, Kurtosis, and first and second half energy over all signal energy.

Results

A three-way ANOVA indicated that during all the cycles, the mean of energy was more and there was a delay in showing the peak of energy in the masseter of the left side with clicked TMJ in MOA group compared to the two other groups, while this pattern occurred inversely in the side with no-clicked TMJ (P < 0.009). The variation of energy was significantly less in MOA group compared to the two other groups in the no-clicked TMJ (P < 0.003). However, the proportion of the first or second part of signal energy to all energy showed that TTH group had less energy in the first part and more energy in the second part in comparison to the two other groups (P < 0.05).

Conclusion

The study showed different changes in the energy distribution of masseter muscle activity during cycles in MOA and TTH. MOA, in contrast to TTH, had lateralization effect on EMG and interacted with TMJ click.

The role of the trigeminal sensory nuclear complex in the pathophysiology of craniocervical dystonia

Isolated focal dystonia is a neurological disorder that manifests as repetitive involuntary spasms and/or aberrant postures of the affected body part. Craniocervical dystonia involves muscles of the eye, jaw, larynx, or neck. The pathophysiology is unclear, and effective therapies are limited. One mechanism for increased muscle activity in craniocervical dystonia is loss of inhibition involving the trigeminal sensory nuclear complex (TSNC). The TSNC is tightly integrated into functionally connected regions subserving sensorimotor control of the neck and face. It mediates both excitatory and inhibitory reflexes of the jaw, face, and neck. These reflexes are often aberrant in craniocervical dystonia, leading to our hypothesis that the TSNC may play a central role in these particular focal dystonias. In this review, we present a hypothetical extended brain network model that includes the TSNC in describing the pathophysiology of craniocervical dystonia. Our model suggests the TSNC may become hyperexcitable due to loss of tonic inhibition by functionally connected motor nuclei such as the motor cortex, basal ganglia, and cerebellum. Disordered sensory input from trigeminal nerve afferents, such as aberrant feedback from dystonic muscles, may continue to potentiate brainstem circuits subserving craniocervical muscle control. We suggest that potentiation of the TSNC may also contribute to disordered sensorimotor control of face and neck muscles via ascending and cortical descending projections. Better understanding of the role of the TSNC within the extended neural network contributing to the pathophysiology of craniocervical dystonia may facilitate the development of new therapies such as noninvasive brain stimulation.

Assessment of the wind-up phenomenon in the equine nociceptive trigeminal system

Repeated sub-threshold nociceptive electrical stimulation resulting in temporal summation of the limb nociceptive withdrawal reflex is a well-established non-invasive model to investigate the wind-up phenomenon in horses. Due to structural similarities of the trigeminal sensory nucleus to the dorsal horn of the spinal cord, temporal summation should be evoked by repeated transcutaneous electrical stimulation of trigeminal afferents. To evaluate this hypothesis repeated transcutaneous electrical stimulation was applied to the supraorbital and infraorbital nerves of 10 horses. Stimulation intensities varied between 0.5 and 1.3 times the trigemino-cervical reflex threshold defined for single stimulation. Evoked electromyographic activity of the orbicularis oculi, splenius and cleidomastoideus muscles was recorded and the signals analysed in the previously established epochs typical to the early and late component of the blink reflex and to the trigemino-cervical reflex. Behavioural reactions were evaluated with the aid of numerical rating scale. The nociceptive late component and the trigemino-cervical reflex were not elicited by sub-threshold intensity repeated transcutaneous electrical stimulation. Furthermore, the median reflex amplitude for the 10 horses showed a tendency to decline over the stimulation train so temporal summation of afferent trigeminal inputs could not be observed. Therefore, the modulation of trigeminal nociceptive processing attributable to repeated Aδ fibre stimulations seems to differ from spinal processing of similar inputs as it seems to have an inhibitory rather than facilitatory effect. Further evaluation is necessary to highlight the underlying mechanism.

Numbness matters: a clinical review of trigeminal neuropathy

AIM

Trigeminal neuropathies are a group of clinical disorders that involve injury to primary first-order neurons within the trigeminal nerve. We review the spectrum of etiologies underlying both painful and non-painful trigeminal neuropathies, with attention to particularly dangerous processes that may elude the clinician in the absence of a meticulous evaluation. Complications and management issues specific to patients with trigeminal neuropathy are discussed.

METHODS

Retrospective literature review.

RESULTS

Facial or intraoral numbness, the hallmark of trigeminal neuropathy, may represent the earliest symptomology of malignancy or autoimmune connective tissue disease as sensory neurons are destroyed. Such numbness, especially if progressive, necessitates periodic evaluation and vigilance even years after presentation if no diagnosis can be made.

CONCLUSIONS

In the routine evaluation of patients with facial pain, the clinician will inevitably be confronted with secondary pathology of the trigeminal nerves and nuclei. The appearance of numbness, even when pain continues to be the most pressing complaint, necessitates clinical assessment of the integrity of all aspects of the trigeminal pathways, which may also include neurophysiologic, radiographic, and laboratory evaluation.

Stress and tension-type headache mechanisms

Stress is widely demonstrated as a contributing factor in tension-type headache (TTH). The mechanisms underlying this remain unclear at present. Recent research indicates the importance of central pain processes in tension-type headache (TTH) pathophysiology. Concurrently, research with animals and healthy humans has begun to elucidate the relationship between stress and pain processing in the central nervous system, including central pain processes putatively dysfunctional in TTH. Combined, these two fields of research present new insights and hypotheses into possible mechanisms by which stress may contribute to TTH. To date, however, there has been no comprehensive review of this literature. The present paper provides such a review, which may be valuable in facilitating a broader understanding of the central mechanisms by which stress may contribute to TTH.

Imaging CNS Modulation of Pain in Humans

Pain is a highly complex and subjective experience that is not linearly related to the nociceptive input. What is clear from anecdotal reports over the centuries and more recently from animal and human experimentation is that nociceptive information processing and consequent pain perception is subject to significant pro- and anti-nociceptive modulations. These modulations can be initiated reflexively or by contextual manipulations of the pain experience including cognitive and emotional factors. This provides a necessary survival function since it allows the pain experience to be altered according to the situation rather than having pain always dominate. The so-called descending pain modulatory network involving predominantly medial and frontal cortical areas, in combination with specific subcortical and brain stem nuclei appears to be one key system for the endogenous modulation of pain. Furthermore, recent findings from functional and anatomical neuroimaging support the notion that an altered interaction of pro- and anti-nociceptive mechanisms may contribute to the development or maintenance of chronic pain states. Research on the involved circuitry and implemented mechanisms is a major focus of contemporary neuroscientific research in the field of pain and should provide new insights to prevent and treat chronic pain states.

Evidence of persistent central sensitization in chronic headaches: a multi-method study

The aim of this study was to investigate central sensitization (CS) in chronic headaches and compare this phenomenon between chronic migraine (CM) and chronic tension-type headache (CTTH). We recruited 69 patients with chronic headaches and 18 control subjects. Questionnaires of headache history, allodynia and the Hospital Anxiety and Depression scale were administered. We recorded thresholds for pinprick and pressure pain, blink (BR) and nociceptive flexion reflex (NFR) R3 component coupled with wind-up ratios. Thresholds for pressure and pinprick pain, BR and NFR R3 were lower and wind-up ratios higher in patients. No differences of CS parameters between CM and CTTH were observed. CS is persistent and prevalent in patients with various types of chronic headache. CS levels are unrelated to the predominant side of pain, disease duration or depression. Neither is CS related to the headache type, suggesting similar mechanisms of headache chronification and chronicity maintaining and possibly explaining clinical similarity of various forms of chronic headache.

Supraspinal modulation of trigeminal nociception and pain

OBJECTIVE

This study examined modulation of trigeminal pain/nociception by 2 supraspinal mechanisms: emotional controls of nociception and diffuse noxious inhibitory controls.

BACKGROUND

Prior research suggests emotional picture viewing (emotional controls) and tonic noxious stimuli (diffuse noxious inhibitory controls) engage supraspinal mechanisms to modulate pain and nociceptive processes. It is currently unknown, however, whether emotional controls modulate trigeminal pain and nociception. Additionally, the influences of emotional controls and diffuse noxious inhibitory controls have not been compared in the same group of participants.

METHODS

Noxious electrodermal stimuli were delivered to the trigeminal nerve using a concentric electrode designed to selectively activate nociceptive fibers. Trigeminal nociception and pain were assessed (34 participants) from the nociceptive blink reflex and pain ratings, respectively. Emotional controls were engaged by presentation of standardized picture stimuli (pleasant, neutral, and unpleasant) shown to reliably evoke pleasure-induced inhibition and displeasure-induced facilitation of pain and nociception. Diffuse noxious inhibitory controls were engaged with a forearm ischemia task.

RESULTS

Trigeminal pain (self-report ratings) and nociception (blinks) were facilitated by unpleasant pictures and inhibited by pleasant pictures. Emotion induction (as assessed from trend analysis) explained 51% of the variance in trigeminal pain and 25% of the variance in trigeminal nociception. Additionally, forearm ischemia inhibited trigeminal pain but not nociception. The baseline vs ischemia comparison explained 17% of the variance in pain report and 0.1% of the variance in blinks. Supraspinal modulation by emotional controls and diffuse noxious inhibitory controls were uncorrelated.

CONCLUSIONS

Emotional controls and diffuse noxious inhibitory controls modulated trigeminal pain and emotional controls modulated trigeminal nociception. These procedures can be used to study supraspinal modulation of nociceptive processing in disorders of the trigeminal pain system, including headache.

Effects of induced stress on experimental pain sensitivity in chronic tension-type headache sufferers

BACKGROUND AND PURPOSE

It has been proposed that stress may contribute to chronic tension-type headache (CTH) through hyperalgesic effects on already sensitized pain pathways in CTH sufferers. This hypothesis could be partially tested by examining effects of stress on mechanical and thermal pain sensitivity in CTH sufferers. Such examinations have not been reported to date.

MATERIALS AND METHODS

In the present study, we measured cephalic and extra-cephalic pressure [pressure-pain threshold (PPT)] and cold-pain thresholds (CPT) in CTH sufferers (n = 8 females, n = 8 males) and healthy control subjects (n = 8 males, n = 7 females) recruited from the general population before and after exposure to a 15-min stressful mental task.

RESULTS

Results indicated that PPT's at head and hand were lower in the CTH compared with control group both before and after task exposure. PPT's and CPT's decreased from pre- to post-task in both groups, with a significantly greater pre- to post-task reduction in cephalic PPT in the CTH compared with control group. Subjective stress increased from pre- to post-task in both groups and did not differ between groups. In the CTH group, stress reactivity was negatively correlated with PPT's, whilst absolute stress levels were positively correlated with pre- to post-task decrease in PPT's.

CONCLUSIONS

The main finding is an enhanced hyperalgesic effect of stress on cephalic pressure-pain sensitivity in the CTH sufferers compared with the healthy controls. The results support the hypothesis that stress may contribute to CTH through hyperalgesic effects on already sensitized pain pathways in CTH sufferers.

Imaging pain modulation in health and disease

PURPOSE OF REVIEW

In this review, we discuss recent advances in pain imaging research. We focus on the involvement of endogenous pain control mechanisms in the healthy central nervous system and the potential contribution of failure within this system for chronic pain states.

RECENT FINDINGS

Nociceptive information processing and related pain perception is subject to substantial pro and antinociceptive modulation. Recent studies demonstrate that this modulation can take place at any stage of ascending information processing. A network of cortical, predominantly mesial and frontal areas, in combination with specific brainstem nuclei, appear to be the key players in the context of endogenous pain modulation. Recent findings from functional and anatomical neuroimaging support the notion that an altered interaction of pro and antinociceptive mechanisms may contribute to the development or maintenance of chronic pain states. The additional use of pharmacological intervention in pain imaging research provides an alternative tool for investigating mechanisms of pain modulation.

SUMMARY

Top-down pain modulation relies on both cortical and subcortical structures. Research on the involved circuitry, including the implemented mechanisms, is a major focus of contemporary neuroscientific research in the field of pain and will provide new insights into the prevention and treatment of chronic pain states.

Habituation to painful stimulation involves the antinociceptive system

The perception of pain results from an interaction between nociceptive and antinociceptive mechanisms. A better understanding of the neural circuitry underlying these physiological interactions provides an important opportunity to develop better treatment strategies for and ultimately even prevent pain. Here, we investigated how repeated painful stimulation over several days is processed, perceived and finally modulated in the healthy human brain. Twenty healthy subjects were stimulated daily with a 20min pain paradigm for 8 consecutive days, and functional MRI performed on days 1, 8 and 22. Repeated painful stimulation over several days resulted in substantially decreased pain ratings to identical painful stimuli. The decreased perception of pain over time is reflected in decreased BOLD responses to nociceptive stimuli in classical pain areas, including thalamus, insula, SII and the putamen. In contrast to this finding, we found that pain-related responses in the rACC, specifically the subgenual anterior cingulate cortex (sgACC), significantly increased over time. Given this area's predominant role in endogenous pain control, this response pattern suggests that habituation to pain is at least in part mediated by increased antinociceptive activity.

Case Series of Four Different Headache Types Presenting as Tooth Pain

Case reports in the literature discuss various headache disorders that present as pain in the face. The current understanding of neuroanatomy and headache mechanisms suggests that headache pain originates within intracranial structures and is then referred to the face, jaws, and teeth. This case series describes four patients, one each with migraine headache, cluster headache, paroxysmal hemicrania, and hemicrania continua, all of which who presented to dentists with the chief complaint of tooth pain. This is the first report of hemicrania continua presenting as tooth pain. It is important that dentists be cognizant of headache disorders so that they may be able to identify headache pains masquerading as toothache.