Pain sensitivity and pain reactivity of pericranial muscles in migraine and tension-type headache
Hartmut Göbel, Lars Weigle, Peter Kropp, Dieter Soyka
Neurological Clinic, University of Kiel, Kiel, Germany Cephalalgia
Göbel H, Weigle L, Kropp P, Soyka D. Pain sensitivity and pain reactivity of pericranial muscles in migraine and tension-type headache. Cephalalgia 1992;12:142-51. Oslo. ISSN 0333-I024 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. • Experimental pain measurement, headache classification, migraine, pericranial muscle tenderness, tension -type headache Hartmut Göbel, Neurological Clinic, University of Kiel, Niemannsweg 147, 2300 Kiel I Germany. Received 14 December 1991, accepted 5 March 1992
For many decades the significance of abnormal muscle contraction to the cause of headache has been investigated and discussed, but conclusive studies documenting this tension factor as a cause have failed to appear (cf. Headache Classification Committee 1988 (I)). Even EMG biofeedback, which aims to reduce muscle tension in view of the assumed etiology, was unconvincing (2). With respect to this, the Headache Classification Committee of the International Headache Society makes reference not to the cause, which ultimately is unknown, but rather to the phenomonology of headache as a basis for the classification. No longer is the term "muscle contraction headache" used, but rather the purely descriptive term "tension-type headache", thus no assumption about a particular cause. Phenomenologically, two types of tension-type headache can be differentiated: one type with muscular factors and another without. This factor, however, does not refer primarily to muscle tension, but rather to the pain sensitivity of pericranial muscles. Accordingly, a differentiation is made between tension-type headache with increased pain sensitivity and headache with normal pain sensitivity of the pericranial muscles. The main problem with this classification, however, is that until now there is insufficient knowledge of the limits of normal tension and pain sensitivity of pericranial musculature. Further, it has not been satisfactorily shown if the classification is relevant with respect to cause, clinical differences or treatment outcome. This study set out to investigate whether experimentally determined pain sensitivity of pericranial musculature in patients with tension-type headache differed from that of migraine patients and healthy individuals. Second, we investigated whether differences in the effect of experimental suprathreshold pain induction on EMG activity of pericranial musculature could be established, and, third, whether subgroups with higher and lower pericranial pain sensitivity within the three diagnostic groups could be found in terms of neurophysiological, psychological and clinical variables. The pain threshold and also the pain sensitivity of pericranial musculature in the entire metrically divided suprathreshold pain sensitivity range was investigated.
Methods
Subjects Twenty-nine healthy individuals, 23 patients with migraine without aura and 20 patients with episodic tension-type headache participated in the study. Particular attention was given to comparability and representation of the groups in recruiting the samples (Table 1). Only in rare instances could patients of the university neurological outpatient department participate in the study because as a rule this patient group consisted of problem patients taking drugs over years and patients with additional concomitant physical or psychical disorders. For this reason a Table 1. Sample characteristics of the three groups examined. The chi-square test was used for nominally scaled variables for testing of significance; variables scaled at intervals were tested using variance analysis. The data of headache symptoms relate to prospective data collected using a headache calendar during the baseline phase of 14 days. They do not present a statistical mean over a long time period, or allow a diagnostical evaluation but they do capacitate a comparison of the groups. NS = not significant. Healthy Migraine Tension-type Significance Basis variables age (years) x 26.2 28.6 23.5 NS s 2.5 10.4 6.4 sex female 18 17 15 NS male 11 6 5 height cm 171.2 172.8 172.4 NS weight kg 65.2 64.3 65. 1 NS Headache symptoms intensity (scale x 26.0 14.8 p = 0.0013 units) s 8.3 6.0 attacks/month x 10.6 14.2 NS s 11.1 12.1 attack duration (h) x 6.2 7.0 NS s 3.7 6.6 Personality satisfaction with life 5.0 4.4 5.3 NS social orientation 6.2 6.3 6.5 NS ambition 5.1 4.5 5.5 NS inhibition 5.0 5.3 4.8 NS excitability 5.7 5.1 5.8 NS aggression 5.7 4.1 4.4 p = 0.0025 stress 4.8 5.5 5.3 NS physical complaints 5.2 5.9 5.6 NS worries about health 3.9 4.6 4.7 NS openness 6.2 5.2 5.5 NS extraversion 5.4 4.4 5.3 NS emotionality 5.6 5.7 5.1 NS Momentary well-being activation 3.9 4.5 6.3 p = 0.009 concentration 5.7 6.6 7.7 p = 0.012 desactivation 3.2 3.2 2.5 NS tiredness 2.4 3.3 2.7 NS numbness 2.0 1.5 1.0 NS extroversion 5.5 5.5 6.9 NS introversion 1.9 1.7 1.9 NS self-confidence 5.8 5.3 6.8 NS elevated mood 5.2 4.4 5.7 NS agitation 2.0 1.7 2.5 NS sensitivity 2.9 3.3 4.0 NS anger .3 .3 1.1 NS fearfulness .6 .9 .7 NS depression .8 1.8 1.6 NS dreaminess 3.2 3.6 2.1 NS Physical symptoms well-being complaints
.
1.6 .40
.
1.6 43
1.8 .49
NS NS
headache screening questionnaire was distributed among students in which students could mark the presence of relevant operationalized diagnostic criteria (9). If these data pointed to a relevant headache disorder, then the students were invited to a neurological examination, on the basis of which the headache was diagnosed. The data in Table I show prospectively collected headache characteristics using a headache calendar for a period of 14 days. The diagnosis of episodic tension-type headache was based not upon these data, but rather on anamnestic, retrospective, statements. Examinations were performed in the headache interval. The 29 healthy subjects were also randomly chosen from the student population. Experimental pain induction at the head Constant pressure measuring 2.9378 megapascal was exerted bilaterally to the temporo-parietal muscle and the temporal muscle. The device used to exert pressure consisted of two individually adjustable circular surface areas of 1.77 mm2 with a blockable spring. At the beginning of stimulus application pressure application was not perceived as painful by the subjects. In the course of time, however, a continual or rather, in terms of its intensity, increasing pain developed, which was scaled from threshold to tolerance point by the subjects (Figs. 1 and 2). The pain was not induced directly by the pressure during this procedure, but probably through a local ischaemia with increasing metabolic disturbance. This constant stimulus causes a progressively increasing pain, the intensity of which covers the entire pain sensitivity range.
Experimental algesimetry During the measurements the participants were seated on a chair with an adjustable headrest and armrest. The laboratory was completely closed off to outside acoustic and visual stimuli. The scaling unit (s, Fig. 2) was placed on a tray mounted on the armrests. The scale, the same as for assessing clinical headache intensity using the headache calendar, was divided into five decades (0: no pain; 1-10: very weak pain; 21-30: medium pain; 31-40: severe pain; 41-50: very severe pain). Patients used a pointer fastened to the scale to indicate the induced pain sensitivity. Movement of the pointer was registered on a three-lead recorder simultaneously with the EMG signals. A 1-min baseline measurement was made preceding stimulus application; the beginning of pain induction was marked by the start of pointer movement. At a pain intensity of 50 (end point) stimulus application was broken off and EMG was registered during a I min post-pain period (3-9). Operationalization of pain sensitivity in the suprathreshold sensitivity range As a measure of pain sensitivity the number of pain scale units per second induced by the pressure algesimeter were computed for each pain intensity category. Since each of the five pain intensity categories contained ten scale units (decades) these were divided by the experimental stimulus time necessary for pain induction of the corresponding decade. This procedure makes it possible to determine an independent variable for each pain intensity category in the entire pain perception range. The greater the parameter the faster the pain intensity units were induced, the greater the pain sensitivity. Summation of the individual parameters produces a total score which gives overall information about the supra-threshold pain sensitivity of pericranial musculature in the entire suprathreshold pain intensity area. Electromyography The electrical activity of selected pericranial muscles was measured, at rest, during experimental pain induction and relaxation, with the Myometer MM2501 (Biometer, Odense, Denmark). In addition, EMG activity was registered during maximal voluntary contraction (without pain induction). When using two independent input channels it was possible to use one channel to register the EMG of the frontal muscle at the right and left of the forehead above the eyes. One electrode each of the above-mentioned channels was localized at the site stated. The second channel was used to register the electrical activity of the right and left masseter and superficial muscles by placing the electrodes below the
zygomatic arc. A neutral electrode was placed on the left ear lobe. These electrode positions were chosen on the basis of experience gathered in comprehensive preliminary tests. These sites produced the strongest reactions during application of experimental pain stimuli. No EMG artifacts due to pointer positioning during scaling were seen. Nuchal musculature proved to be unsuitable because of physical movements (i.e. movement of the shoulders during scaling) and, in particular, voluntary or rather involuntary corrections of the head position. The electrodes used were silver/silver chloride and impregnated with electrode gel. The mean EMG signal was evaluated. This was integrated with a time constant of 0.3 seconds and thereby adapted accordingly. The frequency range was set at 20-1000 Hz. Computing pain-category specific EMG scores For analysis of EMG activity in relation to suprathreshold pain induction the consecutive time periods were considered separately, namely the base-line phase to the start of pain induction, the five suprathreshold pain intensity categories, as well as the relaxation phase following termination of the stimulus application (Fig. 2). To evaluate the data the integral was calculated using the EMG measurement, between the phase duration and the electrical muscle activity. This value was divided by the corresponding time duration in seconds. In this way a pain-category specific mean EMG score was computed that characterizes EMG activity independently of the phase duration (Unit: µV/sec2 x pain unit). Standardized measurement of psychological characteristics and headache-related variables Preceding the experiment, momentary psychological and physical state-of-being were registered quantitatively using the adjective list (10) and the multi-dimensional physical symptom list (11). Following completion of the experiment, the subject's personality traits were registered using the Freiburg Personality Inventory (12). Headache patients also filled out the multi-dimensional Kiel Pain Questionnaire which registered headache-related variables in a standardized fashion on the basis of the IHS headache criteria 9). Results
Comparison of pericranial pain sensitivity Fig. 3 shows the intensity specific pain sensitivity parameters of the pericranial muscles in healthy individuals, patients with migraine without aura and patients with tension-type headache. Patients with
tension-type headache and migraine patients had a tendency toward reduced pain sensitivity of pericranial musculature in comparison to healthy controls. The differences, however, were not significant upon variance analysis. The variability of pain sensitivity of pericranial musculature was elevated in patients with tension-type headache as compared to both other groups. Comparison of electrical skin resistance at rest EMG activity of pericranial musculature at rest, and during maximal contraction The electrical skin resistance at all electrode positions as well as EMG activity at rest and under maximal strain between the three groups showed no significant differences (Table 2). Effects of suprathreshold pain induction at the head on EMG activity of pericranial musculature During experimental pain stimulation by mechanical pressure on the temporal muscle (Figs. 4 and 5), all three groups showed a significant increase in EMG scores between the baseline score and following measurements in the frontal as well as the masseter and superficial muscles (analysis of variance: masseter muscle and superficial muscles: p
Hartmut Göbel, Lars Weigle, Peter Kropp, Dieter Soyka
Neurological Clinic, University of Kiel, Kiel, Germany Cephalalgia
Göbel H, Weigle L, Kropp P, Soyka D. Pain sensitivity and pain reactivity of pericranial muscles in migraine and tension-type headache. Cephalalgia 1992;12:142-51. Oslo. ISSN 0333-I024 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. • Experimental pain measurement, headache classification, migraine, pericranial muscle tenderness, tension -type headache Hartmut Göbel, Neurological Clinic, University of Kiel, Niemannsweg 147, 2300 Kiel I Germany. Received 14 December 1991, accepted 5 March 1992
For many decades the significance of abnormal muscle contraction to the cause of headache has been investigated and discussed, but conclusive studies documenting this tension factor as a cause have failed to appear (cf. Headache Classification Committee 1988 (I)). Even EMG biofeedback, which aims to reduce muscle tension in view of the assumed etiology, was unconvincing (2). With respect to this, the Headache Classification Committee of the International Headache Society makes reference not to the cause, which ultimately is unknown, but rather to the phenomonology of headache as a basis for the classification. No longer is the term "muscle contraction headache" used, but rather the purely descriptive term "tension-type headache", thus no assumption about a particular cause. Phenomenologically, two types of tension-type headache can be differentiated: one type with muscular factors and another without. This factor, however, does not refer primarily to muscle tension, but rather to the pain sensitivity of pericranial muscles. Accordingly, a differentiation is made between tension-type headache with increased pain sensitivity and headache with normal pain sensitivity of the pericranial muscles. The main problem with this classification, however, is that until now there is insufficient knowledge of the limits of normal tension and pain sensitivity of pericranial musculature. Further, it has not been satisfactorily shown if the classification is relevant with respect to cause, clinical differences or treatment outcome. This study set out to investigate whether experimentally determined pain sensitivity of pericranial musculature in patients with tension-type headache differed from that of migraine patients and healthy individuals. Second, we investigated whether differences in the effect of experimental suprathreshold pain induction on EMG activity of pericranial musculature could be established, and, third, whether subgroups with higher and lower pericranial pain sensitivity within the three diagnostic groups could be found in terms of neurophysiological, psychological and clinical variables. The pain threshold and also the pain sensitivity of pericranial musculature in the entire metrically divided suprathreshold pain sensitivity range was investigated.
Methods
Subjects Twenty-nine healthy individuals, 23 patients with migraine without aura and 20 patients with episodic tension-type headache participated in the study. Particular attention was given to comparability and representation of the groups in recruiting the samples (Table 1). Only in rare instances could patients of the university neurological outpatient department participate in the study because as a rule this patient group consisted of problem patients taking drugs over years and patients with additional concomitant physical or psychical disorders. For this reason a Table 1. Sample characteristics of the three groups examined. The chi-square test was used for nominally scaled variables for testing of significance; variables scaled at intervals were tested using variance analysis. The data of headache symptoms relate to prospective data collected using a headache calendar during the baseline phase of 14 days. They do not present a statistical mean over a long time period, or allow a diagnostical evaluation but they do capacitate a comparison of the groups. NS = not significant. Healthy Migraine Tension-type Significance Basis variables age (years) x 26.2 28.6 23.5 NS s 2.5 10.4 6.4 sex female 18 17 15 NS male 11 6 5 height cm 171.2 172.8 172.4 NS weight kg 65.2 64.3 65. 1 NS Headache symptoms intensity (scale x 26.0 14.8 p = 0.0013 units) s 8.3 6.0 attacks/month x 10.6 14.2 NS s 11.1 12.1 attack duration (h) x 6.2 7.0 NS s 3.7 6.6 Personality satisfaction with life 5.0 4.4 5.3 NS social orientation 6.2 6.3 6.5 NS ambition 5.1 4.5 5.5 NS inhibition 5.0 5.3 4.8 NS excitability 5.7 5.1 5.8 NS aggression 5.7 4.1 4.4 p = 0.0025 stress 4.8 5.5 5.3 NS physical complaints 5.2 5.9 5.6 NS worries about health 3.9 4.6 4.7 NS openness 6.2 5.2 5.5 NS extraversion 5.4 4.4 5.3 NS emotionality 5.6 5.7 5.1 NS Momentary well-being activation 3.9 4.5 6.3 p = 0.009 concentration 5.7 6.6 7.7 p = 0.012 desactivation 3.2 3.2 2.5 NS tiredness 2.4 3.3 2.7 NS numbness 2.0 1.5 1.0 NS extroversion 5.5 5.5 6.9 NS introversion 1.9 1.7 1.9 NS self-confidence 5.8 5.3 6.8 NS elevated mood 5.2 4.4 5.7 NS agitation 2.0 1.7 2.5 NS sensitivity 2.9 3.3 4.0 NS anger .3 .3 1.1 NS fearfulness .6 .9 .7 NS depression .8 1.8 1.6 NS dreaminess 3.2 3.6 2.1 NS Physical symptoms well-being complaints
.
1.6 .40
.
1.6 43
1.8 .49
NS NS
headache screening questionnaire was distributed among students in which students could mark the presence of relevant operationalized diagnostic criteria (9). If these data pointed to a relevant headache disorder, then the students were invited to a neurological examination, on the basis of which the headache was diagnosed. The data in Table I show prospectively collected headache characteristics using a headache calendar for a period of 14 days. The diagnosis of episodic tension-type headache was based not upon these data, but rather on anamnestic, retrospective, statements. Examinations were performed in the headache interval. The 29 healthy subjects were also randomly chosen from the student population. Experimental pain induction at the head Constant pressure measuring 2.9378 megapascal was exerted bilaterally to the temporo-parietal muscle and the temporal muscle. The device used to exert pressure consisted of two individually adjustable circular surface areas of 1.77 mm2 with a blockable spring. At the beginning of stimulus application pressure application was not perceived as painful by the subjects. In the course of time, however, a continual or rather, in terms of its intensity, increasing pain developed, which was scaled from threshold to tolerance point by the subjects (Figs. 1 and 2). The pain was not induced directly by the pressure during this procedure, but probably through a local ischaemia with increasing metabolic disturbance. This constant stimulus causes a progressively increasing pain, the intensity of which covers the entire pain sensitivity range.
Experimental algesimetry During the measurements the participants were seated on a chair with an adjustable headrest and armrest. The laboratory was completely closed off to outside acoustic and visual stimuli. The scaling unit (s, Fig. 2) was placed on a tray mounted on the armrests. The scale, the same as for assessing clinical headache intensity using the headache calendar, was divided into five decades (0: no pain; 1-10: very weak pain; 21-30: medium pain; 31-40: severe pain; 41-50: very severe pain). Patients used a pointer fastened to the scale to indicate the induced pain sensitivity. Movement of the pointer was registered on a three-lead recorder simultaneously with the EMG signals. A 1-min baseline measurement was made preceding stimulus application; the beginning of pain induction was marked by the start of pointer movement. At a pain intensity of 50 (end point) stimulus application was broken off and EMG was registered during a I min post-pain period (3-9). Operationalization of pain sensitivity in the suprathreshold sensitivity range As a measure of pain sensitivity the number of pain scale units per second induced by the pressure algesimeter were computed for each pain intensity category. Since each of the five pain intensity categories contained ten scale units (decades) these were divided by the experimental stimulus time necessary for pain induction of the corresponding decade. This procedure makes it possible to determine an independent variable for each pain intensity category in the entire pain perception range. The greater the parameter the faster the pain intensity units were induced, the greater the pain sensitivity. Summation of the individual parameters produces a total score which gives overall information about the supra-threshold pain sensitivity of pericranial musculature in the entire suprathreshold pain intensity area. Electromyography The electrical activity of selected pericranial muscles was measured, at rest, during experimental pain induction and relaxation, with the Myometer MM2501 (Biometer, Odense, Denmark). In addition, EMG activity was registered during maximal voluntary contraction (without pain induction). When using two independent input channels it was possible to use one channel to register the EMG of the frontal muscle at the right and left of the forehead above the eyes. One electrode each of the above-mentioned channels was localized at the site stated. The second channel was used to register the electrical activity of the right and left masseter and superficial muscles by placing the electrodes below the
zygomatic arc. A neutral electrode was placed on the left ear lobe. These electrode positions were chosen on the basis of experience gathered in comprehensive preliminary tests. These sites produced the strongest reactions during application of experimental pain stimuli. No EMG artifacts due to pointer positioning during scaling were seen. Nuchal musculature proved to be unsuitable because of physical movements (i.e. movement of the shoulders during scaling) and, in particular, voluntary or rather involuntary corrections of the head position. The electrodes used were silver/silver chloride and impregnated with electrode gel. The mean EMG signal was evaluated. This was integrated with a time constant of 0.3 seconds and thereby adapted accordingly. The frequency range was set at 20-1000 Hz. Computing pain-category specific EMG scores For analysis of EMG activity in relation to suprathreshold pain induction the consecutive time periods were considered separately, namely the base-line phase to the start of pain induction, the five suprathreshold pain intensity categories, as well as the relaxation phase following termination of the stimulus application (Fig. 2). To evaluate the data the integral was calculated using the EMG measurement, between the phase duration and the electrical muscle activity. This value was divided by the corresponding time duration in seconds. In this way a pain-category specific mean EMG score was computed that characterizes EMG activity independently of the phase duration (Unit: µV/sec2 x pain unit). Standardized measurement of psychological characteristics and headache-related variables Preceding the experiment, momentary psychological and physical state-of-being were registered quantitatively using the adjective list (10) and the multi-dimensional physical symptom list (11). Following completion of the experiment, the subject's personality traits were registered using the Freiburg Personality Inventory (12). Headache patients also filled out the multi-dimensional Kiel Pain Questionnaire which registered headache-related variables in a standardized fashion on the basis of the IHS headache criteria 9). Results
Comparison of pericranial pain sensitivity Fig. 3 shows the intensity specific pain sensitivity parameters of the pericranial muscles in healthy individuals, patients with migraine without aura and patients with tension-type headache. Patients with
tension-type headache and migraine patients had a tendency toward reduced pain sensitivity of pericranial musculature in comparison to healthy controls. The differences, however, were not significant upon variance analysis. The variability of pain sensitivity of pericranial musculature was elevated in patients with tension-type headache as compared to both other groups. Comparison of electrical skin resistance at rest EMG activity of pericranial musculature at rest, and during maximal contraction The electrical skin resistance at all electrode positions as well as EMG activity at rest and under maximal strain between the three groups showed no significant differences (Table 2). Effects of suprathreshold pain induction at the head on EMG activity of pericranial musculature During experimental pain stimulation by mechanical pressure on the temporal muscle (Figs. 4 and 5), all three groups showed a significant increase in EMG scores between the baseline score and following measurements in the frontal as well as the masseter and superficial muscles (analysis of variance: masseter muscle and superficial muscles: p
