123
Puin, 46 (1991) 123-124 0 1991 Elsevier Science Publishers B.V. 0304-3959/91/$03.50
PAIN 01879
Guest Editorial Getting away from simple muscle contraction as a mechanism of tension-type headache Jes Olesen and Rigmor Jensen Department of Neurology, Gentofte Hospital, University of Copenhagen, DK-2900 Hellerup (Denmark)
(Accepted 20 March 1991)
Headache is one of the commonest causes of pain. Only a minority of sufferers display a very distinct symptomatology such as those with migraine or cluster headache. The great majority have a dull aching pain unassociated with other symptoms. In the general population these headaches are called tension headaches, tension probably alluding to tension in the mind as well as tension in the pericranial muscles. Because these headaches are usually mild and known by virtually everyone, there has been a tendency to disregard them, but approximately 3% of the population have daily headaches and 10% weekly headaches. Such severe forms cause a lot of suffering, enormous loss of workdays and quality of life. Previously it was believed that involuntary tonic contraction leading to muscle ischemia was the mechanism of the abnormal nociception. Consequently the term muscle contraction headache was coined some 30 years ago [l]. Virtually nothing was done to evaluate the role of muscle contraction for many years thereafter, but during the last decade several studies have described resting state EMG level. They generally employed primitive EMG techniques and too small experimental groups to allow for detailed conclusions. Nevertheless, they threw doubt upon the concept of marked tonic muscle contraction as the direct cause of headache. The effect of tricyclic antidepressants and other psychotropic drugs as well as the obvious importance of emotional and psychosocial stress factors were also taken to indicate that a central factor must be operating [for review see 31. The International Headache Classification Committee had a hard time trying to classify and define these headaches [2]. Many members of the committee felt that the evidence for a muscular factor was virtually non-existent and that the headaches should be termed idiopathic. Others still believed that muscle contraction mechanisms were of dominating importance. In the end the headaches were termed tension-type to indicate that they are the usual headaches known to everyone as tension headaches,
but without alluding to any specific pathophysiological mechanism [2]. The paper by Schoenen et al. [9] in this issue of headache essentially confirms a previous publication [5] in demonstrating decreased pressure pain thresholds in patients with chronic tension-type headache. But in the study of Schoenen et al. [9] also thresholds in the frontal region as well as over the Achilles tendon were decreased. The earlier study showed that thresholds are also decreased to heat- and cold-induced pain [5]. Together these two studies indicate a generalized and multimodal increase in pain sensitivity in patients with chronic tension-type headache. This could be due to previous long-standing overuse of drugs, but in both studies attempts were done to avoid this. It is also possible that other factors such as anxiety and hidden depression rather than the headache disorder itself explain the findings. Large scale studies are necessary to answer such questions. Schoenen et al. [93, in their discussion, focus exclusively on central mechanisms as an explanation of tension-type headache. This is supported by their extremely important previous finding of decreased exteroceptive silent period in patients with tension-type headache [8] and the modulation of this phenomenon by biofeedback treatment and its variability in relation to the female menstrual cycle in patients with premenstrual headaches [7]. Decreased pressure pain and thermal thresholds probably reflect central phenomena because they are also found outside the head, but in the paper of Schoenen et al. [9] only 50% of the patients had decreased thresholds and in unpublished results (Jensen, Krogh Rasmussen and Olesen) we have seen even less impressive findings in a population-based study. We have also seen previously that pressure dolorimetry is less sensitive than digital palpation [4]. This indicates that central factors cannot alone explain the pain. Furthermore, in order for tension-type headache to be purely central we need to explain why pain is only in the head and not in the rest of the body,
why decreased pain thresholds are only seen in chronic and not in episodic tension-type headache and why only a mirlority of chronic tensit)~l-ty~c headache patients have significantly decreased thresholds (more than 2 S.D.). A purely central hypothesis fails to explain the relation between headache and peripheral factors such as malfunctioning dentures, loss of molars, unphysiologjca1 working position. etc. Schocncn et al. must be credited for their unequivocal demonstration of a central factor in tension-type headache, but probably a much more complicated model is necessary to understand the broad majority of patients [6]. The bad news is therefore that mechanisms of tension-type headache arc complex. The good news is that neuroscicntific investigation of this cxtremely common disorder has begun and that avenues of future research are visible. Clearly there is hope for the future.
References 1 Ad Hoc Committee
on Classification
of headache, J. Am. Med. Assoc..
of Headache. Classification
179 (iYh?)
717-7fX.
Puin, 46 (1991) 123-124 0 1991 Elsevier Science Publishers B.V. 0304-3959/91/$03.50
PAIN 01879
Guest Editorial Getting away from simple muscle contraction as a mechanism of tension-type headache Jes Olesen and Rigmor Jensen Department of Neurology, Gentofte Hospital, University of Copenhagen, DK-2900 Hellerup (Denmark)
(Accepted 20 March 1991)
Headache is one of the commonest causes of pain. Only a minority of sufferers display a very distinct symptomatology such as those with migraine or cluster headache. The great majority have a dull aching pain unassociated with other symptoms. In the general population these headaches are called tension headaches, tension probably alluding to tension in the mind as well as tension in the pericranial muscles. Because these headaches are usually mild and known by virtually everyone, there has been a tendency to disregard them, but approximately 3% of the population have daily headaches and 10% weekly headaches. Such severe forms cause a lot of suffering, enormous loss of workdays and quality of life. Previously it was believed that involuntary tonic contraction leading to muscle ischemia was the mechanism of the abnormal nociception. Consequently the term muscle contraction headache was coined some 30 years ago [l]. Virtually nothing was done to evaluate the role of muscle contraction for many years thereafter, but during the last decade several studies have described resting state EMG level. They generally employed primitive EMG techniques and too small experimental groups to allow for detailed conclusions. Nevertheless, they threw doubt upon the concept of marked tonic muscle contraction as the direct cause of headache. The effect of tricyclic antidepressants and other psychotropic drugs as well as the obvious importance of emotional and psychosocial stress factors were also taken to indicate that a central factor must be operating [for review see 31. The International Headache Classification Committee had a hard time trying to classify and define these headaches [2]. Many members of the committee felt that the evidence for a muscular factor was virtually non-existent and that the headaches should be termed idiopathic. Others still believed that muscle contraction mechanisms were of dominating importance. In the end the headaches were termed tension-type to indicate that they are the usual headaches known to everyone as tension headaches,
but without alluding to any specific pathophysiological mechanism [2]. The paper by Schoenen et al. [9] in this issue of headache essentially confirms a previous publication [5] in demonstrating decreased pressure pain thresholds in patients with chronic tension-type headache. But in the study of Schoenen et al. [9] also thresholds in the frontal region as well as over the Achilles tendon were decreased. The earlier study showed that thresholds are also decreased to heat- and cold-induced pain [5]. Together these two studies indicate a generalized and multimodal increase in pain sensitivity in patients with chronic tension-type headache. This could be due to previous long-standing overuse of drugs, but in both studies attempts were done to avoid this. It is also possible that other factors such as anxiety and hidden depression rather than the headache disorder itself explain the findings. Large scale studies are necessary to answer such questions. Schoenen et al. [93, in their discussion, focus exclusively on central mechanisms as an explanation of tension-type headache. This is supported by their extremely important previous finding of decreased exteroceptive silent period in patients with tension-type headache [8] and the modulation of this phenomenon by biofeedback treatment and its variability in relation to the female menstrual cycle in patients with premenstrual headaches [7]. Decreased pressure pain and thermal thresholds probably reflect central phenomena because they are also found outside the head, but in the paper of Schoenen et al. [9] only 50% of the patients had decreased thresholds and in unpublished results (Jensen, Krogh Rasmussen and Olesen) we have seen even less impressive findings in a population-based study. We have also seen previously that pressure dolorimetry is less sensitive than digital palpation [4]. This indicates that central factors cannot alone explain the pain. Furthermore, in order for tension-type headache to be purely central we need to explain why pain is only in the head and not in the rest of the body,
why decreased pain thresholds are only seen in chronic and not in episodic tension-type headache and why only a mirlority of chronic tensit)~l-ty~c headache patients have significantly decreased thresholds (more than 2 S.D.). A purely central hypothesis fails to explain the relation between headache and peripheral factors such as malfunctioning dentures, loss of molars, unphysiologjca1 working position. etc. Schocncn et al. must be credited for their unequivocal demonstration of a central factor in tension-type headache, but probably a much more complicated model is necessary to understand the broad majority of patients [6]. The bad news is therefore that mechanisms of tension-type headache arc complex. The good news is that neuroscicntific investigation of this cxtremely common disorder has begun and that avenues of future research are visible. Clearly there is hope for the future.
References 1 Ad Hoc Committee
on Classification
of headache, J. Am. Med. Assoc..
of Headache. Classification
179 (iYh?)
717-7fX.
