Pressure pain thresholds and thermal nociceptive thresholds in chronic tension-type headache

The nociceptive thresholds to mechanical and thermal stimuli in patients with chronic tension-type headache were compared. Palpation of pericranial tenderness was performed in 50 patients and a total tenderness score (TTS) was calculated. Palpation was repeated, and pressure pain thresholds (PPTs) were determined with a pressure algometer in the temporal and occipital regions. In 32 of the patients, pain thresholds for heat and cold and limens for detection of non-painful temperature changes were determined in the hands and the temporal regions. Twenty-four healthy volunteers served as controls. Scores obtained by manual palpation (TTS) at the first and second visit were positively correlated. A negative correlation between headache severity and PPT was found in the temporal region. A positive correlation between PPT in the temporal and occipital region was found, and PPT and TTS were negatively correlated. Thermal pain thresholds were consistently less extreme in patients compared to controls, and patients reporting severe headache on the examination day were those most sensitive to thermal pain. No difference was found between patients and controls with respect to detection of temperature changes. A correlation was found between PPT and the corresponding cold pain thresholds, but no correlation could be demonstrated between TTS and thermal pain thresholds. In conclusion, headache patients had decreased pain perception thresholds. Chronic tension-type headache might be a result of dysmodulation of nociceptive impulses, but it is likely that sensitized nociceptors also play a role.     

Muscular Factors are of Importance in Tension-Type Headache

Recent studies have indicated that muscular disorders may be of importance for the development of increased pain sensitivity in patients with chronic tension-type headache. The objective of the present study was to investigate this hypothesis by examining the pain perception in tension-type headache with and without muscular disorders defined as increased tenderness. We examined 28 patients with episodic tension-type headache, 28 patients with chronic tension-type headache, and 30 healthy controls. Pericranial myofascial tenderness was recorded with manual palpation, and pressure pain detection and tolerances in cephalic and extracephalic locations with an electronic pressure algometer. In addition, thermal pain sensitivity and electromyographic activity were recorded. The main result was significantly lower pressure pain detection thresholds and tolerances in all the examined locations in patients with chronic tension-type headache with a muscular disorder compared to those without a muscular disorder. There were no such differences in any of the examined locations when the two subgroups of patients with episodic tension-type headache were compared. Thermal pain sensitivity did not differ between patients with and without a muscular disorder, while electromyographic activity levels were significantly higher in patients with chronic tension-type headache with than in those without a muscular disorder. Our results strongly indicate that prolonged nociceptive stimuli from the pericranial myofascial tissue sensitize the central nervous system and, thereby, lead to an increased general pain sensitivity. Muscular factors may, therefore, be of major importance for the conversion of episodic into chronic tension-type headache. The present study complements the understanding of the important interactions between peripheral and central factors in tension-type headache and may lead to a better prevention and treatment of the most prevalent type of headache.     

Central sensitization in tension-type headache--possible pathophysiological mechanisms

The aim of the present thesis was to investigate the pathophysiology of chronic tension-type headache with special reference to central mechanisms. Increased tenderness to palpation of pericranial myofascial tissues is the most apparent abnormality in patients with tension-type headache. A new piece of equipment, a so-called palpometer, that makes it possible to control the pressure intensity exerted during palpation, was developed. Thereafter, it was demonstrated that the measurement of tenderness could be compared between two observers if the palpation pressure was controlled, and that the Total Tenderness Scoring system was well suited for the scoring of tenderness during manual palpation. Subsequently, it was found that pressure pain detection and tolerance thresholds were significantly decreased in the finger and tended to be decreased in the temporal region in chronic tension-type headache patients compared with controls. In addition, the electrical pain threshold in the cephalic region was significantly decreased in patients. It was concluded that the central pain sensitivity was increased in the patients probably due to sensitization of supraspinal neurones. The stimulus-response function for palpation pressure vs. pain was found to be qualitatively altered in chronic tension-type headache patients compared with controls. The abnormality was related to the degree of tenderness and not to the diagnosis of tension-type headache. In support of this, the stimulus-response function was found to be qualitatively altered also in patients with fibromyalgia. It was concluded that the qualitatively altered nociception was probably due to central sensitization at the level of the spinal dorsal horn/trigeminal nucleus. Thereafter, the prophylactic effect of amitriptyline, a non-selective serotonin (5-HT) reuptake inhibitor, and of citalopram, a highly selective 5-HT reuptake inhibitor, was examined in patients with chronic tension-type headache. Amitriptyline reduced headache significantly more than placebo, while citalopram had only a slight and insignificant effect. It was concluded that the blockade of 5-HT reuptake could only partly explain the efficacy of amitriptyline in tension-type headache, and that also other actions of amitriptyline, e.g. reduction of central sensitization, were involved. Finally, the plasma 5-HT level, the platelet 5-HT level and the number of platelet 5-HT transporters were found to be normal in chronic tension-type headache. On the basis of the present and previous studies, a pathophysiological model for tension-type headache is presented. According to the model, the main problem in chronic tension-type headache is central sensitization at the level of the spinal dorsal horn/trigeminal nucleus due to prolonged nociceptive inputs from pericranial myofascial tissues. The increased nociceptive input to supraspinal structures may in turn result in supraspinal sensitization. The central neuroplastic changes may affect the regulation of peripheral mechanisms and thereby lead to, for example, increased pericranial muscle activity or release of neurotransmitters in the myofascial tissues. By such mechanisms the central sensitization may be maintained even after the initial eliciting factors have been normalized, resulting in the conversion of episodic into chronic tension-type headache. Future basic and clinical research should aim at identifying the source of peripheral nociception in order to prevent the development of central sensitization and at ways of reducing established sensitization. This may lead to a much needed improvement in the treatment of chronic tension-type headache and other chronic myofascial pain conditions.     

Multiple clinical and paraclinical analyses of chronic tension-type headache associated or unassociated with disorder of pericranial muscles

Thirty-two female patients fulfilling the diagnostic criteria of chronic tension-type headache underwent multiple clinical (severity index before and after biofeedback therapy; anxiety score) and paraclinical (pericranial EMG levels and pressure-pain thresholds, temporalis exteroceptive silent period) assessments. Twenty-three patients (72%) had at least one increased EMG level and/or at least one decreased pain threshold and qualified for the subgroup" associated with disorder of pericranial muscles" (code 2.2.1). Nine patients (28%) were within the normal range for both investigations and would have been classified in the subgroup "unassociated with such disorder" (code 2.2.2). No significant differences were found between these two groups of patients for headache severity, anxiety, response to biofeedback therapy or duration of temporalis second exteroceptive silent period. The various clinical and paraclinical parameters were not significantly correlated to each other. It is therefore suggested that the subdivision of chronic tension-type headache in two subgroups based on pericranial EMG levels and/or pain sensitivity might be artificial. Since both of the latter and temporalis silent periods vary independently, they appear complementary in the study of tension-type headache patients and probably represent peripheral abnormalities, which are induced to varying intensities by a common central nervous system dysfunction.     

Increased muscle pain sensitivity in patients with tension-type headache

Nociceptive mechanisms in tension-type headache are poorly understood. The aim was to investigate the pain sensitivity of pericranial muscles and a limb muscle in patients with tension-type headache. Experimental muscle pain was induced by standardized infusions of 0.5 ml of 1 M hypertonic saline into two craniofacial muscles (anterior temporalis (TPA) and masseter (MAS)) and a limb muscle (anterior tibial (TA)) in 24 frequent episodic tension-type headache patients (FETTH), 22 chronic tension-type headache patients (CTTH) and 26 age and gender matched healthy subjects. Headache patients were examined twice, both on days with and on days without headache. The pressure pain thresholds (PPTs) were determined before and after infusions. The subjects continuously reported intensity of saline-induced pain on an electronic visual analogue scale (VAS) and the perceived area of pain was drawn on anatomical maps. Headache patients demonstrated significantly lower PPTs, higher saline-evoked VAS pain scores and greater pain areas than healthy subjects at all the tested muscle sites (P<0.05). There was a significant gender difference for the PPTs in all three groups of participants (P<0.05) and for VAS pain scores in the CTTH patients (P<0.05). There was no difference in pain sensitivity between FETTH and CTTH or between patients with or without headache. In conclusion, the present study demonstrates the presence of generalized pain hypersensitivity both in FETTH and CTTH compared to controls which is unrelated to actual headache status and extends to include responses to longer-lasting stimuli which are clinically highly relevant. Gender differences in deep pain sensitivity seem to be a consistent finding both in healthy controls and patients with tension-type headache.     

Pathophysiological mechanisms of tension-type headache: a review of epidemiological and experimental studies

In this present thesis I have discussed the epidemiology and possible pathophysiological mechanisms of tension-type headache. A population-based study of 1000 subjects randomly selected from a general population, two clinical studies, and a method study of EMG recordings, were conducted. Tension-type headache was the most prevalent form of headache, with a life-time prevalence of 78% in a general adult population. Thirty percent were affected more than 14 days per year and 3% were chronically affected, i.e. had headache at least every other day. Females were more frequently affected than males, and young subjects more frequently affected than older subjects. Females were more sensitive to mechanical pressure pain and revealed more tenderness from pericranial muscles and tendon insertions than males, and young subjects were more pain-sensitive than older subjects. Significantly higher tenderness in pericranial muscles was found in subjects with tension-type headache compared to migraineurs and to subjects without any experience of headache. Tenderness increased significantly with increasing frequency of tension-type headache in both males and females, whereas no such relation was found for mechanical pain thresholds. The applied EMG methodology was fairly reliable and nonpainful, but due to intersubject variability paired studies should be preferred. Subjects with chronic tension-type headache had slightly increased EMG levels during resting conditions and decreased levels during maximal voluntary contraction compared with headache-free subjects, indicating insufficient relaxation at rest and impaired recruitment at maximal activity. In a subsequent clinical, controlled study, the effect of 30 min of sustained tooth clenching was studied. Within 24 h, 69% of patients and 17% of controls developed a tension-type headache. Shortly after clenching, tenderness was increased in the group who subsequently developed headache, whereas tenderness was stable in the group of patients who remained headache-free, indicating that tenderness might be a causative factor of the headache. Likewise, psychophysical and EMG parameters were studied in 28 patients with tension-type headache, both during and outside of a spontaneous episode of tension-type headache. It was concluded that a peripheral mechanism of tension-type headache is most likely in the episodic subform, whereas a secondary, segmental central sensitization and/or an impaired supraspinal modulation of incoming stimuli seems to be involved in subjects with chronic tension-type headache. Prolonged nociceptive stimuli from myofascial tissue may be of importance for the conversion of episodic into chronic tension-type headache. The author emphasizes that tension-type headache is a multifactorial disorder with several concurrent pathophysiological mechanisms, and that extracranial myofascial nociception may constitute only one of them. The present thesis supplements the understanding of the balance between peripheral and central components in tension-type headache, and thereby, hopefully, leads us to a better prevention and treatment of the most prevalent type of headache.     

Dynamic assessment of abnormalities in central pain transmission and modulation in tension-type headache sufferers

OBJECTIVE: To examine and compare central pain processing and modulation in young tension-type headache sufferers with that of matched healthy controls using an induced headache "challenge" paradigm. BACKGROUND: Recent research has suggested that abnormalities in central pain processing and descending pain modulation may contribute to chronic tension-type headache. These abnormalities, if they contribute to headache pathogenesis, should be present in young adult tension-type headache sufferers. Recent research using static measures of physiological variables, such as muscle tenderness and exteroceptive suppression, has identified chronic muscle tenderness as a characteristic of young tension-type headache sufferers, but other central nervous system functional abnormalities may require a dynamic "challenge" to be observed. METHODS: Twenty-four young women meeting the International Headache Society diagnostic criteria for tension-type headache (headache-prone) and a matched group of 24 healthy women who reported fewer than 10 problem headaches per year (control) participated in a double-blind, placebo-controlled, crossover study. Subjects completed jaw clenching and a placebo condition on different days in counterbalanced order. Pericranial muscle tenderness, pressure-pain thresholds on the temporalis, and exteroceptive suppression periods were assessed before and after each procedure. Head pain was recorded for 12 to16 hours following each condition. RESULTS: Headache-prone subjects were more likely than controls to experience headaches after both the jaw clenching and placebo procedures, but neither group was significantly more likely to experience headaches following jaw clenching than placebo. In pretreatment measurements, headache-prone subjects exhibited greater muscle tenderness than controls, but pressure-pain detection thresholds and exteroceptive suppression periods did not differ in the two groups. Control subjects showed increases in muscle tenderness and exteroceptive suppression periods following both the clenching and placebo procedures, whereas headache-prone subjects exhibited no significant changes in any of the physiological measures following either experimental manipulation. CONCLUSIONS: These results confirm previous findings indicating abnormally high pericranial muscle tenderness in young tension headache sufferers even in the headache-free state. In addition, the results suggest that the development of headaches following noxious stimulation is more strongly related to headache proneness and associated abnormalities in central pain transmission or modulation (indexed by pericranial muscle tenderness and exteroceptive suppression responses) than muscle strain induced by jaw clenching.     

Pain sensitivity and pain reactivity of pericranial muscles in migraine and tension-type headache

We investigated whether experimentally determined, suprathreshold pain sensitivity of pericranial musculature in patients with tension-type headache differs from that of migraine patients or from that of healthy subjects. Furthermore, we looked to see whether differences could be found in the effects of experimental pain induction on EMG activity of pericranial musculature and whether subgroups could be discovered with higher and lower pericranial pain sensitivity within the three diagnostic groups in terms of neurophysiological, psychological and clinical variables. In 20 patients with tension-type headache, 23 patients with migraine without aura, and 29 healthy individuals experimental pain was induced in the temporal muscle by mechanical pressure; pain sensitivity in the entire metrically subdivided suprathreshold pain sensitivity range was measured. Surface EMG activity of pericranial muscles was determined before, during and after experimental pain induction. In addition, headache characteristics as well as personality and mood states were determined and recorded in a standardized fashion. There were no significant differences in pain sensitivity of pericranial musculature between the three groups. Patients with tension-type headache showed significantly higher EMG scores during suprathreshold pain stimulation than did migraine patients. EMG scores of healthy subjects fell between these two groups. With respect to pericranial tenderness significant differences in clinical, neurophysiological and psychological variables were found only between subgroups within the group of patients with tension-type headache. The results indicate that significant differences in the examined groups are found not in pain perception but in the processing or reaction to experimental headache stimuli. In patients with tension-type headache subgroups evolve based on pericranial pain sensitivity with quantitatively and/or qualitatively impaired reactions; for this reason diagnostic grouping according to the IHS classification seems to be pathophysiologically relevant. The intraindividual phasic comparison of pain reactions appears to be more important than the absolute interindividual tonic comparison.     

Comparative study with EMG, pressure algometry and manual palpation in tension-type headache and migraine

According to International Headache Society classification criteria, the presence of pericranial muscle disorder in tension-type headache should be evaluated using one of the following methods: EMG, pressure algometry or manual palpation. The purpose of this study was to compare the results of these three methods in 15 patients with episodic tension-type headache, 29 with chronic tension-type headache and 22 presenting migraine without aura compared to those obtained in healthy individuals. Algometric and EMG recordings at the frontalis muscle during mental arithmetic were more impaired in episodic and chronic tension headache patients than in controls and migraine patients. Chronic tension headache patients were significantly impaired at the trapezius muscle in all three tests compared to controls. Our data indicate that when two or three tests were carried out the diagnostic capacity was significantly improved in comparison to only one test. Moreover, since a different pattern could be seen with pain and without pain, the existence of headache at the time of testing should be taken into consideration.     

Possible mechanisms of glyceryl-trinitrate-induced immediate headache in patients with chronic tension-type headache

Nitric oxide (NO) plays an important role in the pathophysiology of primary headaches including chronic tension-type headache (CTTH). Thus, a NO synthase inhibitor reduces headache and muscle hardness while the NO donor glyceryl trinitrate (GTN) causes more headache in patients than in healthy controls. Sensitization of myofascial pain pathways is important in CTTH, and the aim of the present study was to investigate if such mechanisms may also explain GTN-induced immediate headache in patients with CTTH. In a randomized, double-blind, crossover study 16 patients with CTTH and 16 healthy subjects received intravenous infusion of GTN (0.5 microg/kg per min for 20 min) or placebo on two headache-free days separated by at least 1 week. Muscle hardness, myofascial tenderness, mechanical and heat pain thresholds were measured at baseline and at 60 min and 120 min after start of infusion. In patients, GTN infusion resulted in a biphasic response with immediate headache and more pronounced delayed headache. A similar but less pronounced response was seen in controls. There was no difference between GTN and placebo regarding muscle hardness, myofascial tenderness or pressure and heat pain thresholds in either patients or controls (P>0.05). The unchanged sensitivity of pericranial myofascial pain pathways indicates that peripheral and central sensitization is not involved in the mechanisms of GTN-induced immediate headache.     

Heat pain thresholds and cerebral event-related potentials following painful CO2 laser stimulation in chronic tension-type headache

Current opinion concerning the pathophysiology of tension-type headache (TTH) and its related pericranial muscle tenderness proposes a primary role of central sensitization at the level of dorsalhorn/trigeminal nucleus as well as the supraspinal level. Investigation of these phenomena can be conducted using laser-evoked potentials (LEPs), which are objective and quantitative neurophysiological tools for the assessment of pain perception. In the present study we examined features of LEPs, as well as cutaneous heat-pain thresholds to laser stimulation, in relation to the tenderness of pericranial muscles in chronic TTH resulting from pericranial muscle disorder, during a pain-free phase. Twelve patients with TTH and 11 healthy controls were examined using the Total Tenderness Scoring (TTS) system. The stimulus was a laser pulse generated by a CO(2) laser. The dorsum of the hand and the cutaneous zones corresponding to pericranial muscles were stimulated. Subjective perception of stimulus intensity was assessed by a visual analogue scale. Two responses, the earlier named N2a and the last named P2, were considered; the absolute latency was measured at the highest peak of each response. The N2a-P2 components' peak-to-peak amplitude was detected. The heat pain threshold was similar in TTH patients and controls at the level of both the hand and pericranial skin. The TTS scores at almost all pericranial sites were higher in TTH patients than in normal controls. The amplitude of the N2a-P2 complex elicited by stimulation of the pericranial zone was greater in TTH patients than in controls; the amplitude increase was significantly associated with the TTS score. Our findings suggest that pericranial tenderness may be a primary phenomenon that precedes headache, and is mediated by a greater pain-specific hypervigilance at the cortical level.     

Muscle tenderness in pericranial and neck-shoulder region in children with headache. A controlled study

Increased pericranial muscle tenderness is connected with tension-type headache in adults. In children, the importance of muscle tenderness in the pericranial or neck-shoulder region in the pathogenesis of different types of headache is unknown. The present study evaluated muscle tenderness in the pericranial and neck-shoulder region in children with migraine, those with tension-type headache and those without headache. An unselected population-based questionnaire study concerning headache was carried out in 1135 Finnish schoolchildren aged 12 years. Of them, 183 children were randomly selected for a face-to-face interview and a clinical examination. Muscle tenderness was recorded by manual palpation and dolorimeter. Children with migraine had increased overall tenderness, recorded by manual palpation, compared with those without headache. They also self-reported tenderness in the neck-shoulder region during daily activities more often than the children of the other groups. Muscle tenderness was not associated with paediatric tension-type headache. The mean pressure pain thresholds did not differ among the three groups. However, a negative correlation between the total tenderness score and the dolorimeter score was found in each group. In conclusion, children with migraine had increased muscle tenderness at palpation of the pericranial and neck-shoulder muscles and they also reported pain symptoms in the neck-shoulder region most frequently. Instead, increased pericranial and neck-shoulder muscle tenderness was not associated with tension-type headache in children.     

Exteroceptive suppression of temporal muscle activity is normal in chronic tension-type headache and not related to actual headache state

The aim of the present study was to compare the late exteroceptive suppression period (ES₂) of temporalis muscle activity between patients with chronic tension-type headache and healthy controls, and to investigate the influence, if any, of actual headache on ES₂. ES₂ was recorded in 55 patients and in 55 controls with a previously evaluated methodology and analysed by a blinded observer. The first 20 patients were randomly studied on 2 additional days, 1 day with and 1 day without headache. The duration of ES₂ did not differ between patients and controls and did not differ on days with headache compared with days without headache. ES₂ duration was not related to the frequency of headache, headache intensity, age, pericranial muscle tenderness or electrical pain threshold. Our results strongly indicate that ES₂ is normal in chronic tension-type headache and therefore may not be related to the pathophysiology of this disorder.     

Increased pericranial tenderness, decreased pressure pain threshold, and headache clinical parameters in chronic tension-type headache patients

OBJECTIVE: The aim was to investigate whether increased pericranial tenderness or decreased pressure pain threshold (PPT) was related to headache intensity, duration, and frequency in chronic tension-type headache (CTTH). METHODS: Twenty-five CTTH patients and 25 matched controls were studied. A headache diary was kept for 4 weeks to substantiate the diagnosis and record the pain history. Three tenderness (total, cephalic, and neck) scores and PPT at both cephalic and neck points were objectively and blinded assessed. Bodily pain perceived by the patients was assessed with the Short Form-36 questionnaire. RESULTS: CTTH patients showed decreased PPT and increased tenderness as compared with controls (P<0.001). Negative correlations were found between PPT on each point and their respective tenderness scores. Within the CTTH group, neither increased tenderness nor decreased PPT seemed to directly influence headache intensity, frequency or duration; or vice versa. DISCUSSION: Increased tenderness may predispose the patients to other perpetuating factors in inducing headache attacks. Further research is needed to clearly define the role of pericranial tender tissues or other factors in the genesis and maintenance of CTTH.     

Amitriptyline reduces myofascial tenderness in patients with chronic tension-type headache

The tricyclic anti-depressant amitriptyline is widely used in the treatment of chronic tension-type headache. The aim of the present study was to investigate whether the analgesic effect is caused by a reduction of muscle pain or by a general reduction of pain sensitivity. Thirty-three non-depressed patients with chronic tension-type headache were treated with amitriptyline 75 mg/day and with the highly selective serotonin reuptake inhibitor citalopram 20 mg/day in a 32-week, double-blind, placebo-controlled, three-way crossover study. At the end of each treatment period, actual headache intensity and pericranial myofascial tenderness were recorded, pressure pain detection and tolerance thresholds were measured in the finger and in the temporal region and the electrical pain threshold was measured at the labial commissure. Amitriptyline reduced tenderness and headache intensity significantly more than placebo (P=0.01 and P=0.04, respectively). The reduction in tenderness could be ascribed solely to the group of patients who responded to amitriptyline treatment by at least 30% reduction in headache while tenderness was unchanged in non-responders. Amitriptyline did not affect pressure or electrical pain thresholds at any of the examined locations. Citalopram had no significant effect on any of the examined parameters. These findings indicate that amitriptyline elicits its analgesic effect in chronic myofascial pain by reducing the transmission of painful stimuli from myofascial tissues rather than by reducing overall pain sensitivity. We suggest that this effect is caused by a segmental reduction of central sensitization in combination with a peripheral anti-nociceptive action.     

Photophobia and phonophobia in tension-type and cervicogenic headache

Light and sound-induced discomfort and pain thresholds were measured in 26 patients with cervicogenic headache, in 40 patients with tension-type headache, and in 100 headache-free controls. Neither headache group was significantly different as to photophobia and phonophobia, but both were significantly more sensitive to light and sound than controls ( p <0.0001), even when patients were tested in the headache-tree period ( p <0.05). Episodic and chronic tension-type headache had similar photo- and phonophobia thresholds ( p ≥0.7). Tension-type headache patients were more photo- and phonophobic during headache than outside attack ( p <0.05), but this was not true for cervicogenic headache ( p ≥0.56). In cervicogenic headache patients, photophobia ( p <0.05) but not phonophohia ( p =0.28) was greater on the symptomatic side than on the non-symptomatic side.     

Muscular disorders in tension-type headache

In order to evaluate the diagnostic criteria for muscular disorders in tension-type headache, pericranial muscle tenderness and pressure pain thresholds were studied in a random sample population of 735 adults aged 25–64. In addition, quantitative EMGs were recorded in 547 of these subjects. The correlation between the three diagnostic tests was assessed and the discriminality and cut-off points were analysed using Receiver Operating Characteristics analysis. Local tenderness from the temporal muscles was closely related to the total tenderness scores from 14 pairs of muscles. In chronic tension-type headache, tenderness was positively related to EMG and inversely related to pain thresholds. In the episodic form the total tenderness score was inversely related to pain thresholds, whereas no significant relation to EMG was noted. The Receiver Operating Characteristics curves indicated that tenderness recorded by manual palpation was the most specific and sensitive test, whereas EMG and pain thresholds were of limited diagnostic value. Eighty-seven percent of subjects with the chronic, and 66% of subjects with the episodic form were found to have a "muscular disorder" defined as increased tenderness recorded by either manual palpation or pressure algometry and/or increased EMG levels. However, muscle tenderness increased significantly during pain, so the headache state should be considered in future studies. Suggestions for revision of the present diagnostic criteria for muscular disorders are given.     

EMG Activity in Pericranial Muscles During Postural Variation and Mental Activity in Healthy Volunteers and Patients With Chronic Tension Type Headache

EMG activity was recorded over frontalis, temporalis and trapezius muscles in a supine position, a standing position and during a mental task in 32 female patients suffering from chronic tension-type headache and in 20 healthy volunteers. Measurements in patients were made before and after biofeedback therapy. All EMG levels were on average significantly higher in patients than in controls. 62.5% of patients had at least one abnormal EMG level, but only 34% were beyond the normal range, if 1 muscle and 1 recording condition was considered. EMG levels were not correlated with headache severity, anxiety or response to biofeedback treatment. It is therefore suggested that pericranial EMG activity is not pathogenetic in chronic tension type headache, but merely one of several pathophysiologic changes, that are produced by a central dysfunction.     

Clinical features of headache patients with fibromyalgia comorbidity

Our previous study assessed the prevalence of fibromyalgia (FM) syndrome in migraine and tension-type headache. We aimed to update our previous results, considering a larger cohort of primary headache patients who came for the first time at our tertiary headache ambulatory. A consecutive sample of 1,123 patients was screened. Frequency of FM in the main groups and types of primary headaches; discriminating factor for FM comorbidity derived from headache frequency and duration, age, anxiety, depression, headache disability, allodynia, pericranial tenderness, fatigue, quality of life and sleep, and probability of FM membership in groups; and types of primary headaches were assessed. FM was present in 174 among a total of 889 included patients. It prevailed in the tension-type headache main group (35%, p < 0.0001) and chronic tension-type headache subtype (44.3%, p < 0.0001). Headache frequency, anxiety, pericranial tenderness, poor sleep quality, and physical disability were the best discriminating variables for FM comorbidity, with 81.2% sensitivity. Patients presenting with chronic migraine and chronic tension-type headache had a higher probability of sharing the FM profile (Bonferroni test, p < 0.01). A phenotypic profile where headache frequency concurs with anxiety, sleep disturbance, and pericranial tenderness should be individuated to detect the development of diffuse pain in headache patients.     

Initiating mechanisms of experimentally induced tension-type headache

To elucidate possible myofascial mechanisms of tension-type headache, the effect of 30 min of sustained tooth clenching (10% of maximal EMG-signal) was studied in 58 patients with tension-type headache and in 30 age- and sex-matched controls. Pericranial tenderness, mechanical and thermal pain detection and tolerance thresholds and FMG levels were recorded before and after the clenching procedure. Within 24 h, 69% of patients and 17% of controls developed a tension-type headache. Shortly after clenching, tenderness was increased in the group who subsequently developed headache, whereas tenderness was stable in the group of patients who remained headache free. Mechanical pain thresholds evaluated by pressure algometry remained unchanged in the group which developed headache, whereas thresholds increased in the group which did not develop headache Thermal pain detection and tolerance thresholds remained unchanged in both groups. These findings indicate that, though there may be several different mechanisms of tension-type headache, one of them is sustained muscle contraction. A peripheral mechanism of tension-type headache is therefore possible, whereas a secondary segmental central sensitization seems to be involved in subjects with frequent, tension-type headache. Finally, the increase in pressure pain thresholds in patients who did not develop headache suggested that clenching activated their antinociceptive system, whereas those developing headache were, unable to do so.