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Exteroceptive suppression of temporalis muscle activity in patients with fibromyalgia, tension-type headache, and normal controls
Electroencephalography and clinical Neurophysiology 107 (1998) 196–199
Short communication
Exteroceptive suppression of temporalis muscle activity in patients with fibromyalgia, tension-type headache, and normal controls K. Schepelmann a ,*, M. Dannhausen a, I. Ko¨tter b, M. Schabet a, J. Dichgans a a b
Department of Neurology, University of Tu¨bingen, Hoppe-Seyler-Str. 10, D-72076 Tu¨bingen, Germany Department of Internal Medicine II (Rheumatology and Clinical Immunology), University of Tu¨bingen, Ottfried-Mu¨ller-Str. 10, D-72076 Tu¨bingen, Germany Accepted for publication: 18 March 1998
Abstract Changes of the second suppressive period (ES2) of the exteroceptive suppression of the temporalis muscle activity are found in patients with chronic tension-type headache (TTH) and are suggested to reflect an abnormal endogenous pain control system. We investigated whether similar changes are found in patients with the fibromyalgia syndrome (FMS) that is also believed to result from disturbed central pain processing. The ES2 values of 27 patients with FMS were compared with those of 18 patients with TTH and 40 healthy volunteers. The duration of ES2 (±SD) in FMS patients was 30.6 ± 7.5 ms and was not significantly different from the control group (33.1 ± 7.8 ms), whereas it was significantly shortened in TTH patients (22.9 ± 11.5 ms). Our results indicate that, despite similar concepts on the pathophysiology of the two chronic pain disorders, there are no comparable changes of this brain stem reflex activity in FMS. 1998 Elsevier Science Ireland Ltd. All rights reserved Keywords: Pain; Fibromyalgia; Tension-type headache; Exteroceptive suppression
1. Introduction The fibromyalgia syndrome (FMS) is a clinical syndrome of widespread myofascial pain, muscle stiffness, fatigue, sleep disturbances and, often, psychological distress. The diagnosis is entirely clinical and depends on the identification of tender points (Wolfe et al., 1990). The pathophysiology of FMS is not known. Abnormalities in muscle metabolism (Drewes et al., 1993), alterations of the immune system (Goldenberg, 1989a), and a defect in endogenous pain modulating systems (Yunus, 1992) are suggested to be involved, but yet no unifying theory has been elaborated. Since clinical studies have shown the usefulness of tricyclic antidepressants that block the reuptake of serotonin (Goldenberg, 1989b) and levels of serotonin are decreased in serum and cerebrospinal fluid of FMS patients (Russell et al., 1992), it has been suggested that a relative serotonin deficiency leads to central nervous changes that lower the * Corresponding author. Tel.: +49 7071 2982141; fax: +49 7071 296507.
0013-4694/98/$19.00 1998 Elsevier Science Ireland Ltd. All rights reserved PII S0013-4694 (98 )0 0059-5
pain threshold in these patients. FMS shares some aspects with tension-type headache (TTH). Abnormal endogenous pain control has been suggested to be an important pathophysiological factor also in TTH, in addition to increased nociceptive input from pericranial tissue (Olesen, 1991). Furthermore, the most efficient drugs for treatment are serotonin and noradrenalin reuptake inhibiting antidepressants both in TTH (Olesen and Diener, 1996) and in FMS. Since patients with FMS often suffer from headache and the pathophysiological concepts of the two disorders are, in part, similar, we wondered whether a neurophysiologic test that is sensitive for TTH may also be pathologic in FMS patients. The exteroceptive suppression of temporalis muscle activity is a nocifensive reflex consisting of a biphasic inhibition of voluntary contraction of the masticatory muscles (Godaux and Desmedt, 1975). As shown for the masseter muscle, it can be evoked by innocuous stimuli (Cruccu et al., 1989) and by selective activation of nociceptors (Ellrich et al., 1997). The second suppression period (ES2) has been shown to be markedly reduced in TTH (Schoenen et
EEG 97723
K. Schepelmann et al. / Electroencephalography and clinical Neurophysiology 107 (1998) 196–199
al., 1987; Nakashima and Takahashi, 1991; Wallasch and Go¨bel, 1993). It has been suggested that abnormalities of the exteroceptive suppression of temporalis muscle activity reflect disturbances of the endogenous antinociceptive system (Schoenen, 1993), provided by serotonergic neurotransmission in the brain-stem. We therefore measured the ES2 in patients suffering from FMS and compared these values with data from healthy subjects and from patients with chronic TTH.
2. Methods
197
Signals were amplified, filtered (band pass 20 Hz–15 kHz) and rectified. For analysis, 20 full wave rectified recordings were averaged. ES2 was measured between the beginning and the end of an at least 80% decrease of EMG activity/compared to mean pre-stimulus EMG according to previous reports (Schoenen, 1993). 2.3. Statistics The differences in mean ES2 duration between the 3 groups were compared using ANOVA and the Tukey–Kramer test.
2.1. Subjects 3. Results The study was performed on 27 patients (25 female and 2 male) with FMS, 18 patients (11 female and 7 male) with chronic TTH and 40 healthy volunteers (27 female and 13 male). The average age was 49.4 years (range: 29–69) in the FMS group, 37 years (range: 19–57) in the headache group and 45.5 years (range: 24–90) in the control group. FMS patients were seen as outpatients by the Department of Internal Medicine. FMS was diagnosed according to the diagnostic criteria of the American College of Rheumatology (Wolfe et al., 1990). All patients had tenderness at 11 or more of 18 specific tender points and had otherwise normal laboratory test results. None had other chronic illnesses, but 24 patients also suffered from headache that showed the characteristics of TTH. The headache patients were outpatients at the Department of Neurology. Chronic TTH was diagnosed according to the diagnostic criteria of the International Headache Society (IHS, 1988). Neurological examination did not reveal any other neurological disorders. Healthy subjects were voluntary students, their relatives and members of the department, in whom history as well as internal and neurological examination did not reveal any current health disturbances.None of the subjects was taking any kind of medication at the time of examination. Analgesic and/or antidepressive medication was discontinued at least four weeks before.
3.1. Exteroceptive suppression in healthy subjects Since there is no standardized method yet for measuring the duration of the ES2, we decided to establish control values for our laboratory. To rule out systematic errors and influences from situative events we evaluated the effects of gender, age and individual intensity of voluntary contraction of the temporalis muscle. Fig. 1 shows no difference of ES2 duration between male and female volunteers. The age of the volunteers also did not influence the duration of the ES2 systematically (Fig. 2A). The individual intensity of voluntary contraction of the temporalis muscle, given by the mean maximal amplitude of the prestimulus EMG, did not show any impact (Fig. 2B). The mean latency of the ES2 in the control group was 54.2 ± 7.4 ms and the mean duration of ES2 was 33.1 ± 7.8 ms. 3.2. Exteroceptive suppression in TTH and in FMS The mean latency of the ES2 in the TTH group was 56.0 ± 10.5 ms and the mean duration of ES2 was 22.9 ± 11.5 ms. In the FSM group, the mean latency was 53.1 ± 9.4 ms and the mean duration 30.6 ± 7.5 ms. Fig. 3 shows the mean values of ES2 duration for the control group and the
2.2. Recording procedure The exteroceptive suppression of temporalis muscle activity was registered using a standard electrodiagnostic device (Nicolet Viking 1). Surface EMG of the temporal muscle was recorded with self-adhesive silver/silver chloride electrodes on the cleansed skin, impregnated with electrode gel. The recording electrode was placed over the belly of the temporalis muscle, the reference electrode in front of the tragus. During maximal voluntary tooth-clenching, an electrical stimulus of at least 20 mA and 0.2 ms duration was applied to the ipsilateral skin overlying the mental nerve. Intervals between the stimuli of at least 15 s were observed.
Fig. 1. Mean duration of ES2 (±SD) in female (n = 27) and male (n = 13) healthy subjects.
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K. Schepelmann et al. / Electroencephalography and clinical Neurophysiology 107 (1998) 196–199
two groups of patients. Values are significantly (P , 0.0005) reduced in the TTH group, whereas FMS patients show no difference in controls.
4. Discussion The present study provides an electrophysiological examination of a nocifensive brain stem reflex in FMS patients compared with patients with chronic TTH. Furthermore, we examined the influence of age, gender and voluntary effort on test results in order to rule out systematical errors. In our study we could not find any abnormality of the brain-stem reflex in patients with FMS. This is in accordance with data from a small sample of 6 patients previously reported by Schoenen (Schoenen, 1993). However, since the individual values of this test vary considerably, an examination of a greater sample was mandatory. The suppression of the ES2 is well documented in patients with chronic TTH (Schoenen et al., 1987; Nakashima and Takahashi, 1991; Wallasch and Go¨bel, 1993), which was confirmed in our study. An alteration of the ES2 that is hypothetically due to a disturbance of descending inhibition of the trigeminal system could not be found in our patients with FMS. The changes of ES2 therefore seem to be rather specific for TTH. This may be due to the selective trigeminal approach of the brain stem reflex
Fig. 3. Mean duration of ES2 (±SD) in healthy subjects (controls, n = 40), patients with TTH (n = 18), and patients with FMS (n = 27) *P , 0.0005.
investigation. Disturbance of descending inhibition of nociception in FMS may take place solely at the level of the spinal cord. However, since most of our patients complained of generalized pain, including chronic headache, trigeminal involvement is likely. Thus, if the ES2 reflects inhibitory neurotransmission in the brain-stem, our results indicate that the supposed disturbance of endogenous pain control in TTH and FMS may differ in some aspects. So far, no test has been detected, that gives specific pathological results indicating FMS. Blood tests are usually normal, muscular biopsy shows unspecific changes, and routine EMG examination shows no abnormalities. Also the exteroceptive suppression of temporalis muscle activity is of no use as a diagnostic test in FMS patients. However, an abnormal EEG pattern during sleep has been found, that may correspond to the sleep disturbances (Drewes et al., 1995), and evoked potentials after painful laser stimulation suggest an abnormal nociceptive activation (Gibson et al., 1994; Lorenz et al., 1996) in these patients.
Acknowledgements The authors would like to thank Professor Dr. K. Dietz, Institute for Medical Biometry, University of Tu¨bingen, for help with the statistics. References
Fig. 2. Duration of ES2 (ms) depending on age (A) and mean maximal amplitude of prestimulus EMG (B) in healthy subjects.
Cruccu, G., Agostino, R., Inghilleri, M., Manfredi, M. and Ongerboer de Visser, B.W. The masseter inhibitory reflex is evoked by innocuous stimuli and mediated by Ab afferent fibres. Exp. Brain Res., 1989, 77: 447–450. Drewes, A.M., Andreasen, A., Schroder, H.D., Hogsaa, B. and Jennum, P. Pathology of skeletal muscle in fibromyalgia: a histoimmunochemical and ultrastructural study. Br. J. Rheumatol., 1993, 32: 479–483. Drewes, A.M., Gade, K., Nielsen, K.D., Bjerregard, K., Taagholt, S.J. and Svendsen, L. Clustering of sleep electroencephalographic patterns in patients with the fibromyalgia syndrome. Br. J. Rheumatol., 1995, 34: 1151–1156. Ellrich, J., Hopf, H.C. and Treede, R.-D. Nociceptive masseter inhibitory
K. Schepelmann et al. / Electroencephalography and clinical Neurophysiology 107 (1998) 196–199 reflexes evoked by laser radiant heat and electrical stimuli. Brain Res., 1997, 764: 214–220. Gibson, S.J., Littlejohn, G.O., Gorman, M.M., Helme, R.D. and Granges, G. Altered heat pain thresholds and cerebral event-related potentials following painful CO2 laser stimulation in subjects with fibromyalgia syndrome. Pain, 1994, 58: 185–193. Godaux, E. and Desmedt, J.E. Exteroceptive suppression and motor control of the masseter and temporalis muscles in normal man. Brain Res., 1975, 85: 447–458. Goldenberg, D.L. Fibromyalgia and its relation to chronic fatigue syndrome, viral illness and immune abnormalities. J. Rheumatol., 1989a, Suppl. 19: 91–93. Goldenberg, D.L. A review of the role of tricyclic medications in the treatment of fibromyalgia syndrome. J. Rheumatol., 1989b, Suppl. 19: 137–139. IHS (International Headache Society) Classification and diagnostic criteria for headache disorders, cranial neuralgias and facial pain. Cephalalgia, 1988, 8 (Suppl. 7): 1–96. Lorenz, J., Grasedyck, K. and Bromm, B. Middle and long latency somatosensory evoked potentials after painful laser stimulation in patients with fibromyalgia syndrome. Electroenceph. clin. Neurophysiol., 1996, 100: 165–168. Nakashima, K. and Takahashi, K. Exteroceptive suppression of the masseter, temporalis and trapezius muscles produced by mental nerve stimulation in patients with chronic headaches. Cephalalgia, 1991, 11: 23–28. Olesen, J. Clinical and pathophysiological observations in migraine and
199
tension-type headache explained by integration of vascular, supraspinal and myofascial inputs. Pain, 1991, 46: 125–132. Olesen, J. and Diener, H.-C. Tension-type and cervicogenic headache. In: T. Brandt, L. R. Caplan, J. Dichgans, H.-C. Diener and C. Kennard (Eds.), Neurological Disorders. Course and Treatment. Academic Press, San Diego, CA, 1996: 29–35. Russell, I.J., Vaeroy, H., Javors, M.A. and Nyberg, F. Cerebrospinal fluid biogenic amine metabolites in fibromyalgia/fibrositis syndrome and rheumatoid arthritis. Arthritis Rheum., 1992, 35: 550–556. Schoenen, J. Exteroceptive suppression of temporalis muscle activity in patients with chronic headache and in normal volunteers: methodology, clinical and pathophysiological relevance. Headache, 1993, 33: 3–17. Schoenen, J., Jamart, B., Gerard, P., Lenarduzzi, P. and Delwaide, P.J. Exteroceptive suppression of temporalis muscle activity in chronic headache. Neurology, 1987, 37: 1834–1836. Wallasch, T.-M. and Go¨bel, H. Exteroceptive suppression of temporalis muscle activity: findings in headache. Cephalalgia, 1993, 13: 11–14. Wolfe, F., Smythe, H.A., Yunus, M.B., Bennett, R.M., Bombardier, C., Goldenberg, D.L., Tugwell, P., Campbell, S.M., Abeles, M. and Clark, P. The American College of Rheumatology 1990. Criteria for the Classification of Fibromyalgia. Report of the Multicenter Criteria Committee. Arthritis Rheum., 1990, 33: 160–172. Yunus, M.B. Towards a model of pathophysiology of fibromyalgia: aberrant central pain mechanisms with peripheral modulation. J. Rheumatol., 1992, 19: 846–850.
Short communication
Exteroceptive suppression of temporalis muscle activity in patients with fibromyalgia, tension-type headache, and normal controls K. Schepelmann a ,*, M. Dannhausen a, I. Ko¨tter b, M. Schabet a, J. Dichgans a a b
Department of Neurology, University of Tu¨bingen, Hoppe-Seyler-Str. 10, D-72076 Tu¨bingen, Germany Department of Internal Medicine II (Rheumatology and Clinical Immunology), University of Tu¨bingen, Ottfried-Mu¨ller-Str. 10, D-72076 Tu¨bingen, Germany Accepted for publication: 18 March 1998
Abstract Changes of the second suppressive period (ES2) of the exteroceptive suppression of the temporalis muscle activity are found in patients with chronic tension-type headache (TTH) and are suggested to reflect an abnormal endogenous pain control system. We investigated whether similar changes are found in patients with the fibromyalgia syndrome (FMS) that is also believed to result from disturbed central pain processing. The ES2 values of 27 patients with FMS were compared with those of 18 patients with TTH and 40 healthy volunteers. The duration of ES2 (±SD) in FMS patients was 30.6 ± 7.5 ms and was not significantly different from the control group (33.1 ± 7.8 ms), whereas it was significantly shortened in TTH patients (22.9 ± 11.5 ms). Our results indicate that, despite similar concepts on the pathophysiology of the two chronic pain disorders, there are no comparable changes of this brain stem reflex activity in FMS. 1998 Elsevier Science Ireland Ltd. All rights reserved Keywords: Pain; Fibromyalgia; Tension-type headache; Exteroceptive suppression
1. Introduction The fibromyalgia syndrome (FMS) is a clinical syndrome of widespread myofascial pain, muscle stiffness, fatigue, sleep disturbances and, often, psychological distress. The diagnosis is entirely clinical and depends on the identification of tender points (Wolfe et al., 1990). The pathophysiology of FMS is not known. Abnormalities in muscle metabolism (Drewes et al., 1993), alterations of the immune system (Goldenberg, 1989a), and a defect in endogenous pain modulating systems (Yunus, 1992) are suggested to be involved, but yet no unifying theory has been elaborated. Since clinical studies have shown the usefulness of tricyclic antidepressants that block the reuptake of serotonin (Goldenberg, 1989b) and levels of serotonin are decreased in serum and cerebrospinal fluid of FMS patients (Russell et al., 1992), it has been suggested that a relative serotonin deficiency leads to central nervous changes that lower the * Corresponding author. Tel.: +49 7071 2982141; fax: +49 7071 296507.
0013-4694/98/$19.00 1998 Elsevier Science Ireland Ltd. All rights reserved PII S0013-4694 (98 )0 0059-5
pain threshold in these patients. FMS shares some aspects with tension-type headache (TTH). Abnormal endogenous pain control has been suggested to be an important pathophysiological factor also in TTH, in addition to increased nociceptive input from pericranial tissue (Olesen, 1991). Furthermore, the most efficient drugs for treatment are serotonin and noradrenalin reuptake inhibiting antidepressants both in TTH (Olesen and Diener, 1996) and in FMS. Since patients with FMS often suffer from headache and the pathophysiological concepts of the two disorders are, in part, similar, we wondered whether a neurophysiologic test that is sensitive for TTH may also be pathologic in FMS patients. The exteroceptive suppression of temporalis muscle activity is a nocifensive reflex consisting of a biphasic inhibition of voluntary contraction of the masticatory muscles (Godaux and Desmedt, 1975). As shown for the masseter muscle, it can be evoked by innocuous stimuli (Cruccu et al., 1989) and by selective activation of nociceptors (Ellrich et al., 1997). The second suppression period (ES2) has been shown to be markedly reduced in TTH (Schoenen et
EEG 97723
K. Schepelmann et al. / Electroencephalography and clinical Neurophysiology 107 (1998) 196–199
al., 1987; Nakashima and Takahashi, 1991; Wallasch and Go¨bel, 1993). It has been suggested that abnormalities of the exteroceptive suppression of temporalis muscle activity reflect disturbances of the endogenous antinociceptive system (Schoenen, 1993), provided by serotonergic neurotransmission in the brain-stem. We therefore measured the ES2 in patients suffering from FMS and compared these values with data from healthy subjects and from patients with chronic TTH.
2. Methods
197
Signals were amplified, filtered (band pass 20 Hz–15 kHz) and rectified. For analysis, 20 full wave rectified recordings were averaged. ES2 was measured between the beginning and the end of an at least 80% decrease of EMG activity/compared to mean pre-stimulus EMG according to previous reports (Schoenen, 1993). 2.3. Statistics The differences in mean ES2 duration between the 3 groups were compared using ANOVA and the Tukey–Kramer test.
2.1. Subjects 3. Results The study was performed on 27 patients (25 female and 2 male) with FMS, 18 patients (11 female and 7 male) with chronic TTH and 40 healthy volunteers (27 female and 13 male). The average age was 49.4 years (range: 29–69) in the FMS group, 37 years (range: 19–57) in the headache group and 45.5 years (range: 24–90) in the control group. FMS patients were seen as outpatients by the Department of Internal Medicine. FMS was diagnosed according to the diagnostic criteria of the American College of Rheumatology (Wolfe et al., 1990). All patients had tenderness at 11 or more of 18 specific tender points and had otherwise normal laboratory test results. None had other chronic illnesses, but 24 patients also suffered from headache that showed the characteristics of TTH. The headache patients were outpatients at the Department of Neurology. Chronic TTH was diagnosed according to the diagnostic criteria of the International Headache Society (IHS, 1988). Neurological examination did not reveal any other neurological disorders. Healthy subjects were voluntary students, their relatives and members of the department, in whom history as well as internal and neurological examination did not reveal any current health disturbances.None of the subjects was taking any kind of medication at the time of examination. Analgesic and/or antidepressive medication was discontinued at least four weeks before.
3.1. Exteroceptive suppression in healthy subjects Since there is no standardized method yet for measuring the duration of the ES2, we decided to establish control values for our laboratory. To rule out systematic errors and influences from situative events we evaluated the effects of gender, age and individual intensity of voluntary contraction of the temporalis muscle. Fig. 1 shows no difference of ES2 duration between male and female volunteers. The age of the volunteers also did not influence the duration of the ES2 systematically (Fig. 2A). The individual intensity of voluntary contraction of the temporalis muscle, given by the mean maximal amplitude of the prestimulus EMG, did not show any impact (Fig. 2B). The mean latency of the ES2 in the control group was 54.2 ± 7.4 ms and the mean duration of ES2 was 33.1 ± 7.8 ms. 3.2. Exteroceptive suppression in TTH and in FMS The mean latency of the ES2 in the TTH group was 56.0 ± 10.5 ms and the mean duration of ES2 was 22.9 ± 11.5 ms. In the FSM group, the mean latency was 53.1 ± 9.4 ms and the mean duration 30.6 ± 7.5 ms. Fig. 3 shows the mean values of ES2 duration for the control group and the
2.2. Recording procedure The exteroceptive suppression of temporalis muscle activity was registered using a standard electrodiagnostic device (Nicolet Viking 1). Surface EMG of the temporal muscle was recorded with self-adhesive silver/silver chloride electrodes on the cleansed skin, impregnated with electrode gel. The recording electrode was placed over the belly of the temporalis muscle, the reference electrode in front of the tragus. During maximal voluntary tooth-clenching, an electrical stimulus of at least 20 mA and 0.2 ms duration was applied to the ipsilateral skin overlying the mental nerve. Intervals between the stimuli of at least 15 s were observed.
Fig. 1. Mean duration of ES2 (±SD) in female (n = 27) and male (n = 13) healthy subjects.
198
K. Schepelmann et al. / Electroencephalography and clinical Neurophysiology 107 (1998) 196–199
two groups of patients. Values are significantly (P , 0.0005) reduced in the TTH group, whereas FMS patients show no difference in controls.
4. Discussion The present study provides an electrophysiological examination of a nocifensive brain stem reflex in FMS patients compared with patients with chronic TTH. Furthermore, we examined the influence of age, gender and voluntary effort on test results in order to rule out systematical errors. In our study we could not find any abnormality of the brain-stem reflex in patients with FMS. This is in accordance with data from a small sample of 6 patients previously reported by Schoenen (Schoenen, 1993). However, since the individual values of this test vary considerably, an examination of a greater sample was mandatory. The suppression of the ES2 is well documented in patients with chronic TTH (Schoenen et al., 1987; Nakashima and Takahashi, 1991; Wallasch and Go¨bel, 1993), which was confirmed in our study. An alteration of the ES2 that is hypothetically due to a disturbance of descending inhibition of the trigeminal system could not be found in our patients with FMS. The changes of ES2 therefore seem to be rather specific for TTH. This may be due to the selective trigeminal approach of the brain stem reflex
Fig. 3. Mean duration of ES2 (±SD) in healthy subjects (controls, n = 40), patients with TTH (n = 18), and patients with FMS (n = 27) *P , 0.0005.
investigation. Disturbance of descending inhibition of nociception in FMS may take place solely at the level of the spinal cord. However, since most of our patients complained of generalized pain, including chronic headache, trigeminal involvement is likely. Thus, if the ES2 reflects inhibitory neurotransmission in the brain-stem, our results indicate that the supposed disturbance of endogenous pain control in TTH and FMS may differ in some aspects. So far, no test has been detected, that gives specific pathological results indicating FMS. Blood tests are usually normal, muscular biopsy shows unspecific changes, and routine EMG examination shows no abnormalities. Also the exteroceptive suppression of temporalis muscle activity is of no use as a diagnostic test in FMS patients. However, an abnormal EEG pattern during sleep has been found, that may correspond to the sleep disturbances (Drewes et al., 1995), and evoked potentials after painful laser stimulation suggest an abnormal nociceptive activation (Gibson et al., 1994; Lorenz et al., 1996) in these patients.
Acknowledgements The authors would like to thank Professor Dr. K. Dietz, Institute for Medical Biometry, University of Tu¨bingen, for help with the statistics. References
Fig. 2. Duration of ES2 (ms) depending on age (A) and mean maximal amplitude of prestimulus EMG (B) in healthy subjects.
Cruccu, G., Agostino, R., Inghilleri, M., Manfredi, M. and Ongerboer de Visser, B.W. The masseter inhibitory reflex is evoked by innocuous stimuli and mediated by Ab afferent fibres. Exp. Brain Res., 1989, 77: 447–450. Drewes, A.M., Andreasen, A., Schroder, H.D., Hogsaa, B. and Jennum, P. Pathology of skeletal muscle in fibromyalgia: a histoimmunochemical and ultrastructural study. Br. J. Rheumatol., 1993, 32: 479–483. Drewes, A.M., Gade, K., Nielsen, K.D., Bjerregard, K., Taagholt, S.J. and Svendsen, L. Clustering of sleep electroencephalographic patterns in patients with the fibromyalgia syndrome. Br. J. Rheumatol., 1995, 34: 1151–1156. Ellrich, J., Hopf, H.C. and Treede, R.-D. Nociceptive masseter inhibitory
K. Schepelmann et al. / Electroencephalography and clinical Neurophysiology 107 (1998) 196–199 reflexes evoked by laser radiant heat and electrical stimuli. Brain Res., 1997, 764: 214–220. Gibson, S.J., Littlejohn, G.O., Gorman, M.M., Helme, R.D. and Granges, G. Altered heat pain thresholds and cerebral event-related potentials following painful CO2 laser stimulation in subjects with fibromyalgia syndrome. Pain, 1994, 58: 185–193. Godaux, E. and Desmedt, J.E. Exteroceptive suppression and motor control of the masseter and temporalis muscles in normal man. Brain Res., 1975, 85: 447–458. Goldenberg, D.L. Fibromyalgia and its relation to chronic fatigue syndrome, viral illness and immune abnormalities. J. Rheumatol., 1989a, Suppl. 19: 91–93. Goldenberg, D.L. A review of the role of tricyclic medications in the treatment of fibromyalgia syndrome. J. Rheumatol., 1989b, Suppl. 19: 137–139. IHS (International Headache Society) Classification and diagnostic criteria for headache disorders, cranial neuralgias and facial pain. Cephalalgia, 1988, 8 (Suppl. 7): 1–96. Lorenz, J., Grasedyck, K. and Bromm, B. Middle and long latency somatosensory evoked potentials after painful laser stimulation in patients with fibromyalgia syndrome. Electroenceph. clin. Neurophysiol., 1996, 100: 165–168. Nakashima, K. and Takahashi, K. Exteroceptive suppression of the masseter, temporalis and trapezius muscles produced by mental nerve stimulation in patients with chronic headaches. Cephalalgia, 1991, 11: 23–28. Olesen, J. Clinical and pathophysiological observations in migraine and
199
tension-type headache explained by integration of vascular, supraspinal and myofascial inputs. Pain, 1991, 46: 125–132. Olesen, J. and Diener, H.-C. Tension-type and cervicogenic headache. In: T. Brandt, L. R. Caplan, J. Dichgans, H.-C. Diener and C. Kennard (Eds.), Neurological Disorders. Course and Treatment. Academic Press, San Diego, CA, 1996: 29–35. Russell, I.J., Vaeroy, H., Javors, M.A. and Nyberg, F. Cerebrospinal fluid biogenic amine metabolites in fibromyalgia/fibrositis syndrome and rheumatoid arthritis. Arthritis Rheum., 1992, 35: 550–556. Schoenen, J. Exteroceptive suppression of temporalis muscle activity in patients with chronic headache and in normal volunteers: methodology, clinical and pathophysiological relevance. Headache, 1993, 33: 3–17. Schoenen, J., Jamart, B., Gerard, P., Lenarduzzi, P. and Delwaide, P.J. Exteroceptive suppression of temporalis muscle activity in chronic headache. Neurology, 1987, 37: 1834–1836. Wallasch, T.-M. and Go¨bel, H. Exteroceptive suppression of temporalis muscle activity: findings in headache. Cephalalgia, 1993, 13: 11–14. Wolfe, F., Smythe, H.A., Yunus, M.B., Bennett, R.M., Bombardier, C., Goldenberg, D.L., Tugwell, P., Campbell, S.M., Abeles, M. and Clark, P. The American College of Rheumatology 1990. Criteria for the Classification of Fibromyalgia. Report of the Multicenter Criteria Committee. Arthritis Rheum., 1990, 33: 160–172. Yunus, M.B. Towards a model of pathophysiology of fibromyalgia: aberrant central pain mechanisms with peripheral modulation. J. Rheumatol., 1992, 19: 846–850.