Neuroimaging in headache

The Challenges in Clinical Diagnosis of Trigeminal Neuralgia: A Review

The lack of established laboratory tests or biomarkers for trigeminal neuralgia (TN) makes diagnosing this relatively rare condition extremely challenging. Trigeminal nerve compression observable on magnetic resonance imaging may indicate TN, but many patients do not have visible lesions or compression. In particular, TN may be confused with migraine, cluster headache, temporomandibular disorder, and other types of headache. An accurate diagnosis is imperative for proper treatment since these conditions do not respond to the same treatment. Many symptoms of these headaches can be vague or overlap, and clinicians depend in large measure on the subjective reports of their patients. Nevertheless, it is imperative to diagnose TN better, which can cause excruciating pain, reduce the quality of life, and even result in disability. It is possible that TN is underestimated.

Facial presentations of primary headache disorders

Background

Many patients with mid-face or lower face craniofacial pain are diagnosed, based on accompanying signs and symptoms and features other than location, as either atypical migraines or atypical TACs. Distinguishing features of headache disorders as a cause of facial pain include the temporal pattern of pain, associated symptoms including light and sound sensitivity and nausea, cranial autonomic symptoms, and the lack of local triggering among others.

Results

An intraoral neurovascular pain has been observed, and was termed neurovascular orofacial pain (NVOP). Due to its location, and signs imitating dental pulpitis, it has great diagnostic and therapeutic importance for differentiating NVOP from dental pathology. The hypothesized mechanism is neurogenic inflammatory activation within the space confined by dentine around the dental pulp, expressed in strong paroxysmal pain and typical allodynia to cold foods.

Conclusion

Facial manifestations of headache disorders and primary facial pain disorders share common trigeminal nerve input, yet they are highly distinct disorders. Somatotopic segregation may occur at the level of the trigeminal nucleus, thalamus, and somatosensory cortex, and distinct ionic or neurochemical signaling pathways may be involved. Further investigation of facial presentations of headache disorders has the potential to provide new insight into the interface between headache and facial pain.

Migraine is associated with altered processing of sensory stimuli

Migraine is associated with derangements in perception of multiple sensory modalities including vision, hearing, smell, and somatosensation. Compared to people without migraine, migraineurs have lower discomfort thresholds in response to special sensory stimuli as well as to mechanical and thermal noxious stimuli. Likewise, the environmental triggers of migraine attacks, such as odors and flashing lights, highlight basal abnormalities in sensory processing and integration. These alterations in sensory processing and perception in migraineurs have been investigated via physiological studies and functional brain imaging studies. Investigations have demonstrated that migraineurs during and between migraine attacks have atypical stimulus-induced activations of brainstem, subcortical, and cortical regions that participate in sensory processing. A lack of normal habituation to repetitive stimuli during the interictal state and a tendency towards development of sensitization likely contribute to migraine-related alterations in sensory processing.

Functional neuroimaging of primary headache disorders

Until recently, primary headache disorders, such as migraine and cluster headache were considered to be vascular in origin. However, advances in neuroimaging techniques, such as positron emission tomography, single photon emission computed tomography and functional magnetic resonance imaging have augmented the growing clinical evidence that these headaches are primarily driven from the brain. This review covers functional imaging studies in migraine, cluster headache, rarer headache syndromes and experimental head pain. Together with newer techniques, such as voxel-based morphometry and magnetic resonance spectrometry, functional imaging continues to play a role in elucidating and targeting the neural substrates in each of the primary headache syndromes.

Mid infrared microspectroscopic mapping and imaging: a bio-analytical tool for spatially and chemically resolved tissue characterization and evaluation of drug permeation within tissues

The combination of the two classical biophysical methods, microscopy and infrared spectroscopy, has led to the development of a potent analytical technology termed infrared microspectroscopy. It combines high lateral resolution as obtained by microscopy and the chemical identification of the sample components by infrared spectroscopy. The two approaches mainly utilized in microspectroscopy are the mapping and the imaging techniques, which are introduced and presented. Especially, since the development of so called focal plane array detectors, which are implemented in the imaging methods (microspectroscopic imaging) has become a promising bio-analytical tool for ultrastructural medical diagnostics, due to the fact that the time required for analyzing a sample has been reduced dramatically and the lateral resolution improved to approximately 4 microm. Mid infrared microscopy allows a direct access to spatially resolved molecular and structural information of the analyzed area. The image contrast is generated on the basis of the tissue's intrinsic biochemical composition. The current investigation shows how mid infrared microspectroscopic mapping and imaging is used for the bio-analytical characterization and identification of specific molecular components of a tissue sample at high lateral resolution of a few microns (approaching the mid infrared diffraction limit). Furthermore, the potential of these methods for monitoring the penetration and distribution of drugs within biological tissues are presented. Due to the fact, that mid infrared microspectroscopy is a noninvasive, nondestructive technique for the analyzed sample, requiring no complicated and time consuming staining procedures, it is a convenient method for histological and pathological investigations, allowing the generation of a huge amount of biochemical information not yet available with other nonvibrational techniques. The strength of the presented microscopic technique is the fact that the infrared images are directly comparable to outcomes of classical histological staining procedures and can be interpreted by nonspectroscopists.

Brain activity during stimulation of the trigeminal nerve with noxious heat

OBJECTIVE

The aim of this study was to observe areas of brain activation with painful hot stimulation to the trigeminal nerve.

STUDY DESIGN

Nine healthy pain-free women (mean age 26.2 +/- 6.9 yrs) with a natural, regular menstrual cycle participated in the study. Whole-brain functional magnetic resonance imaging (fMRI) data were acquired for each participant on day 2 or 3 after the onset of menses using echo-planar imaging at 1.5T with near-isotropic spatial resolution and a temporal resolution of 4 s.

RESULTS

Whole-brain fMRI with a Peltier thermode inside the head coil yielded a feasible imaging protocol with little disturbance from the thermode. Painful thermal stimulation of the left trigeminal system activated discrete brain regions within the insula, cingulate gyrus, thalamus, inferior parietal lobe/postcentral gyrus, right middle and inferior frontal gyri, cuneus, precuneus, and precentral gyrus.

CONCLUSION

Painful stimulation of the trigeminal nerve resulted in activation of similar brain areas generally known for pain processing of painful peripheral stimulation.

The contribution of neuroimaging techniques to the understanding of supraspinal pain circuits: implications for orofacial pain

The aim of this article was to give an overview of the current knowledge of supraspinal pain mechanisms derived from neuroimaging studies, and to present data related to chronic orofacial pain disorders. The available studies implied that the anterior cingulate cortex plays a role in the emotional-affective component of pain, as well as in pain-related attention and anxiety. The somatosensory cortices may be involved in encoding spatial, temporal, and intensity aspects of noxious input. The insula may mediate both affective and sensory-discriminative aspects of the pain experience. The thalamus appears to be a multifunctional relay system. The prefrontal cortex has been implied in the pain-related attention processing; it does not have intensity encoding properties. Chronic pain conditions were associated with increased activity in the somatosensory cortices, anterior cingulate cortex, and the prefrontal cortex, and with decreased activity in the thalamus. Few neuroimaging studies used experimental stimuli to the trigeminal system or included orofacial pain patients. However, the available studies appeared to be in agreement with those using stimuli to other body parts and those concerning other chronic pain conditions. Overall, the available data suggest that chronic (orofacial) pain states may be related to a dysfunctional brain network and may involve a compromised descending inhibitory control system. The somatosensory cortices, anterior cingulate cortex, thalamus, and prefrontal cortex may play a vital role in the pathophysiology of chronic pain and should be the main focus of future neuroimaging studies in chronic pain patients.

Functional brain imaging in hemicrania continua: implications for nosology and pathophysiology

Hemicrania continua is a strictly unilateral, continuous headache of mild to moderate intensity, with superimposed exacerbations of moderate to severe intensity that are accompanied by trigeminal autonomic features and migrainous symptoms. The syndrome is exquisitely responsive to indomethacin. Its clinical phenotype overlaps with that of the trigeminal autonomic cephalalgias and migraine, in which the hypothalamus and the brain stem, respectively, have been postulated to play central pathophysiologic roles. A recent positron-emission tomography study of a cohort of patients with hemicrania continua demonstrated significant activation of the contralateral posterior hypothalamus and ipsilateral dorsal rostral pons in association with the headache of hemicrania continua. In addition, there was activation of the ipsilateral ventrolateral midbrain, which extended over the red nucleus and the substantia nigra and bilateral pontomedullary junction. No intracranial vessel dilatation was obvious.

Functional neuroimaging of primary headache disorders

Until recently, primary headache disorders such as migraine and cluster headache were considered to be vascular in origin. However, advances in neuroimaging techniques, such as positron emission tomography, single photon emission computerized tomography, and functional magnetic resonance imaging, have augmented the growing clinical evidence that these headaches are primarily driven from the brain. This review covers functional imaging studies in migraine, cluster headache, rarer headache syndromes, and experimental head pain. Together with newer techniques, such as voxel-based morphometry and magnetic resonance spectrometry, functional imaging continues to play a role in elucidating and targeting the neural substrates in each of the primary headache syndromes.

Role of neuroimaging in our understanding of the pathogenesis of primary headaches

This article reviews new advances in neuroimaging of primary headaches. Imaging of the brain is reaching a new stage of maturity as the basic neural systems that participate in the pathogenesis of headaches are identified. Given the rapid advances in functional neuroimaging, it is no surprise that recent studies have supported the neurovascular theory of migraine and cluster headache. It is clear that functional neuroimaging will continue to be of paramount importance and ultimately may serve as the bridge between molecular and clinical domains in the field of headache research.

Functional neuroimaging of primary headache disorders

Until recently, primary headache disorders such as migraine and cluster headache were considered to be vascular in origin. However, advances in neuroimaging techniques, such as positron emission tomography, single photon emission computerized tomography, and functional magnetic resonance imaging, have augmented the growing clinical evidence that these headaches are primarily driven from the brain. This review covers functional imaging studies in migraine, cluster headache, rarer headache syndromes, and experimental head pain. Together with newer techniques, such as voxel-based morphometry and magnetic resonance spectrometry, functional imaging continues to play a role in elucidating and targeting the neural substrates in each of the primary headache syndromes.

Pain mechanisms and their disorders

The purpose of this article is to summarise how functional imaging techniques have changed our understanding of normal and abnormal pain mechanisms, how they inform a change in clinical practice and to speculate on possible future clinical uses.

Molecular Mechanisms of Migraine

Migraine is a common complex disorder that affects a large portion of the population and thus incurs a substantial economic burden on society. The disorder is characterized by recurrent headaches that are unilateral and usually accompanied by nausea, vomiting, photophobia, and phonophobia. The range of clinical characteristics is broad and there is evidence of comorbidity with other neurological diseases, complicating both the diagnosis and management of the disorder. Although the class of drugs known as the triptans (serotonin 5-HT(1B/1D) agonists) has been shown to be effective in treating a significant number of patients with migraine, treatment may in the future be further enhanced by identifying drugs that selectively target molecular mechanisms causing susceptibility to the disease.Genetically, migraine is a complex familial disorder in which the severity and susceptibility of individuals is most likely governed by several genes that may be different among families. Identification of the genomic variants involved in genetic predisposition to migraine should facilitate the development of more effective diagnostic and therapeutic applications. Genetic profiling, combined with our knowledge of therapeutic response to drugs, should enable the development of specific, individually-tailored treatment.

Facial migraine in a rhinological setting

This study aims to investigate the incidence of migraine involving the face in a rhinology clinic and to describe its characteristics. It is a study of a cohort of 973 patients consecutively presenting to the outpatient clinic with symptoms of facial pain and/or rhinosinusitis. The study subgroup consisted of patients with facial pain and migraine excluding cluster headache and paroxysmal hemicrania. We studied the features of 51 patients who had facial pain with migraine. The diagnosis was based on the criteria used by the International Headache Society and was also supported by the outcome and response to treatment after a mean of 2 years and 2 months. Of the 973 consecutive patients, 409 (42%) had symptoms of facial pain and/or head pain or pressure. Fifty-one (12%) had migraine. Of these, 39 (76%) had unilateral pain and, in 12 (24%), it was bilateral. The distribution affected the forehead and/or eye or cheek in 32 (63%) patients. Twenty-four (47%) had migraine isolated to the second division of the trigeminal nerve. Twelve per cent of patients attending a rhinology clinic with facial pain had migraine. Of particular interest were the 6% of patients with facial pain who had migraine confined to the second division of the trigeminal nerve. This entity is not widely recognized and has rarely been described in the literature.

Paroxysmal hemicrania and cluster headache: two discrete entities or is there an overlap?

Paroxysmal hemicrania has been described as an excruciating unilateral pain, which is usually ocular and frontotemporal with short-lasting (2-45 min), frequent attacks (usually more than five per day); with marked autonomic features (rhinorrhoea, nasal congestion, conjunctival injection, lacrimation) and unilateral to the pain. A response to indomethacin is essential using the current criteria for the diagnosis. It is a rare condition but when it occurs it is misdiagnosed as being due to sinusitis. A retrospective analysis of 11 patients seen in the period 1995-2001 suggests that there is an overlap between paroxysmal hemicrania and cluster headache. Four patients had all the characteristics of paroxysmal hemicrania and responded to indomethacin. Four other patients fulfilled the criteria except for the frequency and length of the attacks. They only had one attack per day and these lasted more than 2 h. Another patient had all the symptoms of paroxysmal hemicrania and did not respond to indomethacin, but responded to triptans and pizotifen. Patients with cluster headache typically respond to these. Two patients were unable to continue taking indomethacin owing to severe gastrointestinal upset. In the same period, we also had 30 patients with cluster headaches. There is increasing evidence that paroxysmal hemicrania and cluster headache share a similar pathogenesis and that they may not always be so discrete in either their response to indomethacin or their periodicity.

Functional imaging of pain perception

The application of functional imaging techniques has revolutionized the field of human pain physiology and has elaborated the understanding of mechanisms involved in pain processing at the cortical and subcortical levels. With these insights, new therapeutic interventions are being developed in the treatment of acute and chronic pain conditions.

Electrophysiological evidence for trigeminal neuron sensitization in patients with migraine

The electrically elicited corneal reflex is a useful tool for exploring the trigeminal system in humans and it may provide additional evidence pointing to a dysfunction of this system in migrainous patients. Tactile perception, corneal reflex and pain thresholds were studied in 48 migraine without aura patients during pain-free periods and compared with those observed in 24 controls. Twenty-eight of the patients had strictly unilateral headache, while the other 20 had bilateral or side-shifting pain during attacks. Both migraine subgroups (bilateral and unilateral) showed significantly lower thresholds compared with controls. The lowest values were observed on the symptomatic side of unilateral migraine patients. These findings suggest that sensorimotor mechanisms and/or pain control systems at the trigeminal level are impaired in migraine. The bilateral location of these abnormalities seems to point to a centrally located dysfunction.