Tension-type headache. Comparison with migraine without aura and cervicogenic headache. The Vågå study of headache epidemiology

Transcription

1 Tension-type headache. Comparison with migraine without aura and cervicogenic headache. The Vågå study of headache epidemiology Ottar Sjaastad, MD, PhD a,b Leiv Sigmund Bakketeig, MD c a Department of Neurology, St. Olavs Hospital, Trondheim University Hospitals (NTNU), Trondheim, Norway b Vågå Communal Health Centre, Vågåmo, Norway c Norwegian Institute of Public Health, Nydalen, Oslo, Norway Corresponding author: Ottar Sjaastad Gautes gate 12 - N-7030 Trondheim eylert.brodtkorb@ntnu.no Invited paper Summary The aim of the present study was to describe the prevalence of tension-type headache (T-TH) in rural Norway, and 1838 citizens aged years were included. Features indicating neck involvement were also looked for. T-TH was compared with migraine without aura and with cervicogenic headache (CEH) considering both these features and typical migraine traits. Face-to-face interviews were carried out, based on an elaborate questionnaire. The IHS criteria, first version, were used for T-TH diagnosis. A T-TH prevalence of 34% was found. In T-TH and migraine without aura, typical CEH features, such as reduced range of motion in the neck and mechanical provocation of pain, were far less prominent than in CEH. Typical migraine traits, e.g. photophobia, were much less frequently present in T-TH and CEH than in migraine without aura. T-TH is, in all probability, not a CEH variant and vice versa. KEY WORDS: cervicogenic headache, migraine without aura, neck pain, persistent neck complaint with subsequent posterior headache, tension-type headache. Introduction The term tension headache originated somewhere along the way, but the present authors do not know exactly where or when. That there have been uncertainty and misgivings regarding this term, can for example be seen from commentaries on the 1962 Ad Hoc Committee criteria (1). Heyck (2), who at a later stage became a member of this committee (1969), felt that it was hard for a central European to accept this term. Heyck was one of the cleverest headache clinicians ever. Later, the term was changed to tension-type headache (T-TH) (3,4). The typical T-TH picture (3,4) also extractable from the IASP description (5) roughly seems to be: a tightening, bilateral, non-pulsating headache of mild-moderate intensity accompanied by few, if any, general autonomic features. Most workers in the field now would probably agree with this description. Nevertheless, T-TH does not seem to have clear-cut boundaries. Symptomatologically, it may infringe upon the borders of migraine without aura (MwoA). T-TH may even, as presented nowadays, consist of more than one entity. The present work is an integral part of the Vågå study of headache epidemiology. The prevalence of T-TH at grass roots level is probably only incompletely known. This may partly be due to the fact that cervicogenic headache (CEH) is not accepted/recognised in some pertinent circles. The principal aim of this study was to identify, to the best of our knowledge, genuine cases of T-TH in this circumscribed, geographical area. Since it has been claimed over and over again that nuchal traits may be found frequently in both T-TH and MwoA, and not only in CEH, a comparison of nuchal features in the three headaches is carried out. Typical migraine traits have also been included in the comparison of the three headaches, to make it more complete. As regards symptomatology, genuineness has been preferred over numbers in cases of diagnostic conflict, and such conflicts inevitably arise. Data for the less genuine T-TH cases will, however, be presented separately, in order to give an idea of the total magnitude of T-TH in this area. Materials and methods The field work of the Vågå study (6) was carried out during the period Vågå had 3907 citizens just prior to the start of the study. All accessible citizens in the age range years were invited to participate in the study, and of these, 1838 (88.6%) could be included. The study protocol (7) involved face-to-face interviews, based on an elaborate headache questionnaire (which the examined individuals were not even allowed to see), plus a meticulous physical/neurological examination of the face, head, and neck, and a short-version neurological examination of the rest of the body. If deemed necessary, a thorough neurological examination would be carried out, and, in such cases, even supplementary studies, like MRI and CT, might be added. In the present study, intensity of pain was graded according to a recently published, sensitive 0-6+ scale (8). On this scale, 3+ to 5+ correspond to the IHS levels mild to severe. The mean intensity in the Vågå series was Features indicative of cervical abnormality, which we will refer to as the cervical factor (CF) (9), were calculated for Functional Neurology 2008; 23(2):

2 O. Sjaastad et al. each participant. The CF is based on the presence of features/findings in relation to following items: i) Range of motion in the neck (ROM), i.e. rotation (9); ii) Skin-roll test in the shoulder area (10); iii-v) Precipitation of pain by graded external pressure (3-4 kg): against the tendon insertions in the occipital area, against the splenius and upper trapezius area, and against the facet joints (9). The CF as such and the skin-roll test were free variables; the CF is graded from 0 to 5+. In headache-free individuals in Vågå (n=246), the mean CF was 0.42+, whereas in the total study population it was Tension-type headache and MwoA (and other primary headaches) were diagnosed according to the IHS, first version (3), which was in current use at the time. The correct categorisation of MwoA and T-TH is cumbersome. For prevalence estimation, cases with T-TH coexisting with a clinically separable MwoA were naturally included. If there seemed to be one headache only, but with properties attributable to both T-TH and MwoA, this headache was considered non-classifiable in the present context. Such cases are not included in either of the rubrics T-TH or MwoA, but will be presented as a separate group. When considering symptomatology, on the other hand, only pure T-TH cases were included, i.e. those in which MwoA had been ruled out, since it was realised that both examiner and participant might be unable to decipher adequately the symptoms of T-TH in the presence of MwoA. CEH was diagnosed according to the criteria of the CHISG, version I (11), which was the one in current use at the time. Anaesthetic blockades were not part of the examination, and consequently not of the criteria used in this context. A quantitative scale was also introduced, with 6.0+ (fulfilment of all criteria) as the highest grade. CHISG CEH criteria (12) were also calculated in each T-TH case and MwoA case. For attack frequency, a 10-point scale was applied, with daily headache and one attack a year as the extremes. Other anamnestic parameters collected included: age at onset, total duration of T-TH, prevailing intensity, jabs/ stabbing pain [this was compared with migraine, in which jabs (icepick-like pain, 13) have been supposed to occur more frequently than in the population at large], location of initial and maximal pain of attack, and nuchal symptoms and signs. Migrainous symptoms, like nausea, vomiting, and pulsatile pain, were also investigated. Symptoms were characterised in various ways, nausea, for example, being present: always; frequently; rarely; never. The methodological problems concerning the always/frequently/rarely/never issue were considerable. The combination: always / frequently seems most suitable for representing the solitary clinical feature, like nausea. The always / frequently combination was compared with its opposite, i.e., rarely/never. The results of the two modes of expression (i.e. pairs of alternatives) should, more or less, coincide. If so, only one figure is given the higher one. If, instead, the results differ more than just marginally which they not infrequently did both figures are considered, and a mean is used. It should be appreciated that if the three alternatives always / frequently / rarely were combined, the ensuing level would be high, in all probability too high. If only always was used, the result would be low, probably far too low. This method of reasoning is, of course, no guarantee that the alternative always / frequently will show a correct value. Two deviations from the IHS criteria were made. First, we did not feel comfortable with our own palpation technique for disorder of the pericranial musculature (3). No results are, therefore, reported concerning and (3). Nor has a subclassification into chronic and episodic T-TH been carried out, because the temporal pattern can change during life, even more than once. In a not inconsiderable group, there was some uncertainty regarding the temporal pattern. Only lifetime prevalence data are given. The diagnostic procedure was validated: A) Blinded recheck of 100 records; B) Blinded re-check of 41 individuals (7), carried out a mean of 14.8 months (range: 4-23 months) after examination I. The subjects in group A were blinded for name, sex, age, occupation, family history, and diagnosis. This study was accepted by the regional ethics committee and the State Data Inspectorate, and all participants gave their signed informed consent. Results The pain in T-TH was relatively weak showing a mean of 3.1, corresponding to just above mild (Table I). The number of pain days varied markedly. On average, > 3 Table I - General information on tension-type headache and headaches with which it can be confused (plus migraine with aura). T-TH CEH MwoA M+A Age at onset, years Age at examination, years Duration of headache, years ca 17 ca 17 ca 22 ca 23 Sex ratio, F/M* Mean intensity (scale: 0-6+)** ***4.0*** Jabs/stabs 4 * (%) Abbreviations and symbols: T-TH=tension-type headache; CEH=cervicogenic headache; MwoA=migraine without aura; M+A=migraine with aura. * 1.06 in the entire Vågå series (7); ** For grading, see text; *** 4.5+, if cases without a pain phase (with aura only) were excluded; 4 * In controls: 35% (7). 72 Functional Neurology 2008; 23(2): 71-76

3 Tension-type headache in Vågå alternatives were ticked on the scale of frequency. A frequency of between one attack per two months and one attack per week was ticked by 52%; and between one attack per three months and two attacks per week was ticked by 75%. Prevalence In 478 cases, the T-TH criteria seemed to be fulfilled, without any admixture of MwoA: i.e. in 26% of the total Vågå series ( pure cases). There were 271 females and 207 males in this group (57% females and 43% males); F/M ratio: 1.31 (Table I). The average age at onset was: 25 (range: 19-65) years. In 137 cases, a coexistence of genuine T-TH and MwoA was believed to be present. The total number of T-TH cases in Vågå, therefore, seemed to be 615; prevalence: 34% (females: 377; males: 238, or 61% versus 39%; F/M ratio: 1.58). Some non-decipherable cases of a sort of amalgamation of T-TH/MwoA were observed: 45 cases in the total Vågå series (or 2.5%). Migrainous traits Regardless of the mode used for presenting the frequency of migrainous traits, e.g. photophobia, a palpable difference seemed to exist between T-TH and MwoA. Migrainous symptoms, like phonophobia and pulsating pain were relatively rare in T-TH, but far from absent (Table II). These symptoms seemed to be milder than in migraine; the feeling of explosion / disintegration in the head, when the pulsating quality of the pain is at its peak, that is occasionally observed in MwoA, was almost non-existent in T-TH/CEH. Migrainous symptoms generally seemed to be present to a similar extent in T-TH and CEH, while the values in both of these headaches generally differed widely from those observed in migraine (Table II). The response to bending forwards also seemed to follow these general lines (Table II). Nausea seemed to be present >4 times more frequently in MwoA than in T-TH/CEH. Accentuation upon physical activity was most frequently found in MwoA, but for this trait the difference vs the other headaches seemed to be less marked. The presence of local autonomic signs (Table II) was equally rare in the three headaches. Cervicogenic traits Typical cervicogenic traits are detailed in Table III (over). The pattern seemed to be that T-TH and MwoA were generally comparable as regards these traits, with only minor/moderate differences emerging between them. However, the trait of unilaterality clearly distinguished T-TH from MwoA; it should be emphasised that unilaterality is a main criterion in MwoA, whereas bilaterality is a criterion in T-TH. The second characteristic trend, evident from Table III, was that the values of these traits were clearly higher in CEH than in T-TH/MwoA. For posterior onset of pain, the difference between the CEH and T-TH values showed a factor of >3; for ipsilateral shoulder complaint, a factor of >5; and for radicular arm pain, a factor of >10. For both T-TH and MwoA, the levels of the cervicogenic features were similar to those of controls in fields where control values could be obtained; e.g. ROM and CF (Table III). Pain provocation from the neck, subjectively as well as objectively, was a prominent feature in CEH but not in T-TH/MwoA. This difference between T-TH and CEH was actually a major one. The mean number of CEH criteria fulfilled differed vastly in T-TH/MwoA and CEH (Table III). One reason why this number of criteria was relatively high in MwoA (compared to T-TH) is that unilaterality is also a criterion of MwoA, but not of T-TH. Without the laterality criterion, Table II - Migrainous features and local autonomic features (% of cases) in the three headache forms. Feature T-TH CEH MwoA Nausea 9 8 (5*/10**) 39 (46*/32**) Vomiting 6 (2*/9**) 5 13 (16*/10**) Throbbing*** (49 4 *) 81 Accentuation upon physical activity Phonophobia (24*/31**) 79 (84*/74**) Photophobia (15*/22**) 68 (73*/62**) Bending forwards: Increase in pain Increase in throbbing Extra symptoms: until resting again Duration of pain >72 hours 61 Negative (obligatory) Local autonomic features Lacrimation Conjunctival injection Nasal secretion Abbreviations and symbols: T-TH=tension-type headache; CEH=cervicogenic headache; MwoA=migraine without aura; M+A=migraine with aura; * Based on: Always/frequent, see text; ** Based on: The opposite of never / rarely, see text; *** Explosions in the head at pain maximum, synchronised with the pulse, were noted more often in MwoA (8%) than in T-TH (1.3%) and CEH (2%); 4 * 20%,throbbing rather regularly. Rarely / mild, not in recent years etc. in 49% of the cases. Functional Neurology 2008; 23(2):

4 O. Sjaastad et al. Table III - Cervicogenic traits in the three headache forms. Variable T-TH MwoA CEH Skin-roll test (mm)* Rotation, neck: a) 15, reduction (%)** a) 10, reduction (%) b) deficit in, mean*** CF: (0-5+) 4* Shoulder discomfort, ss (%) Arm discomfort, diffuse, ss (%) 7 8 7*)100 5 * Arm pain, radicular, ss (%) Pain onset, posteriorly (%) Unilaterality (%) Pain provocation from neck: Subjectively (%) Objectively (%) 6 * ca 1 ca CEH criteria, mean no. (0-6+) *)6.0 7 * Feeling of tension, neck (%) Feeling of stiffness, neck (%) Abbreviations and symbols: T-TH=tension-type headache; CEH=cervicogenic headache; MwoA=migraine without aura; M+A=migraine with aura; ss=symptomatic side; * Mean, Vågå material: 15.0±5.9 (10); ** Vågå material, headache-free individuals (n=246): 22%; *** Mean, Vågå material (n=1838): 6.2 ; 4 * Mean Vågå material: 0.79+; 5 * Among those with adequate information; 6 * Tendon insertions, nuchal area; 7 * 5.93, if three slightly doubtful cases are taken into account. the total sum of CEH criteria fulfilled would have been more similar in T-TH and MwoA. Stabs (jabs) occurred frequently in all these forms of headache; jabs do not seem to be useful in distinguishing between them (Table I). Pain intensity was lowest in T-TH (Table I). Both migraine with aura and MwoA were seemingly more severe than CEH. Feelings of tension and stiffness in the neck (not CEH criteria) were of similar magnitude in T-TH and MwoA (Table III). These levels were somewhat lower in the individuals with no headache in Vågå (i.e. 46%) than in the subjects with T-TH and MwoA. Validation Re-check of records (n=100). Among the 100 files rechecked, 33 concerned T-TH cases. In 20 of these cases, T-TH was the only headache present, while in the other 13 cases, it coexisted with other headaches: migraine with and without aura (n=11); CEH (n=1); neuralgiform headache (n=1). There seemed to be complete concurrence between the results at the two examinations in 29 cases (88% of the cases) and complete or partial disagreement in the other four, the latter being deemed failures. Kappa statistics showed a value of: (p<0.0001). Re-check of individuals (n=41). Of the 41 individuals reexamined, T-TH was a diagnostic possibility in six. Five had shown T-TH or T-TH(?) on examination I, of whom three showed a more or less identical headache at examination II (A&B, Table IV). In one individual, the symptoms had increased and MwoA was suspected (D). In another individual, the symptoms had abated to the extent that this patient, at most, seemed to present only a borderline headache (C). In the sixth individual, the trend observed was the reverse, T-TH probably not actually having been present at examination I (E). A similar/ identical headache thus seemed to be present, at follow up, in three cases, or 50% of those considered. The Kappa value was nevertheless rather high: (p<0.01), because the finding of T-TH- free individuals is reflected in the statistics. The discrepancy between the two examinations could be due to a real evolution of the complaints, given the relatively long observation time; alternatively, the individuals may have explained their complaints in different Table IV - Validation. Comparison of first and second examination in six possible tension-type headache patients (out of a total of 41 individuals re-assessed). Pattern Type of constellation on Number examination I / examination II A +/+ 1 B +?/+? 2 C +/+? 1 D +/+ MwoA(?) 1 E 0/+ 1 Total 6 Abbreviations and symbols: +=suggestive of tension-type headache; 0=not suggestive of tension-type headache; MwoA=migraine without aura. 74 Functional Neurology 2008; 23(2): 71-76

5 Tension-type headache in Vågå ways on the two occasions, or the investigator may have interpreted the narrative differently on the two occasions. While a Kappa value of is comforting, this result can be viewed from another angle: for a clinician, 50% diagnostic accuracy is far from ideal. Discussion Prevalence Tension-type headache is probably the least distinct and most poorly defined of the major, recurrent headaches. T-TH is partly characterised by negative criteria. It has also been described as a wastebasket type of diagnosis. Nevertheless, it has the reputation of being the most prevalent recurrent headache, with a prevalence ranging from 30 to 78% in various investigations, according to the IHS (4); in other words, a rather alarming difference of >250%. The prevalence of T-TH is highly dependent upon the correctness of the borders separating it from MwoA and CEH. It sounds like a sigh when Lance, in a somewhat different context (14), wrote:...no trouble in agreeing on the diagnosis of cluster headache and migraine with aura but found difficulty in finding a dividing line between migraine and tension-type headache. This was written in 1993, after the advent of the IHS criteria (3). In the present study, the prevalence of T-TH was 26% if only the pure cases were calculated, and 34% if cases mixed with MwoA were included. These are much lower figures than those presented in studies from recent years that have used similar techniques, i.e. face-toface interviews: 67% (15) and 69% (lifetime prevalence) (16, 17). Even if we were to add the cases that were a sort of an amalgamation of MwoA and T-TH, the total in the present study (ca 37%) would still not reach such high values. One particular factor may have influenced the numerical T-TH/MwoA balance in the geographical area explored: this is, so to speak, a virgin area as regards the pharmacological approach to these headaches; in particular, regular drug consumption is rare. Typical early-phase migraine traits may have been effaced by drug therapy in areas with high drug consumption, the ultimate headache pattern bearing more resemblance to T-TH. In Vågå, MwoA may have kept the original migraine characteristics to a higher extent, the prevalence in Vågå being: MwoA: 31%; migraine with aura: 9.7% (18). No firm conclusions can be reached with regard to the total impact of the reduced consumption of analgesics in Vågå. Two other factors have contributed to a numerical reduction of T-TH in our series: both CEH (4.1%) (19) and persistent neck complaint with subsequent, transient, posterior headache (6.6%) (20) have been presented under such headings as integral parts of the Vågå study and have, at least partly, been excluded from the T-TH domain this applies particularly to the latter group. If we had added these groups, the prevalence could have been around 45%. The sum of T-TH and migraine with and without aura prevalence may be of interest. In two previous, comparable studies, it was 83% (15) and 84% (16), respectively. In Vågå, it was around 75%. Had CEH + persistent neck complaints (19, 20) been added, i.e %, this would have taken the total to around 85%. Therefore, the sum may be strikingly similar, but the subgrouping differs. Distinction from MwoA and CEH Unilaterality is not included among the T-TH criteria, whereas it is a characteristic trait of both MwoA and CEH. Nevertheless, indirectly, unilaterality may emerge as a factor in clinical T-TH series. Situations may arise in which the bilaterality criterion becomes superfluous, because a satisfactory number of the remaining criteria has already been fulfilled in a given case. Unilaterality (15,21,22) has, probably indirectly, become a feature of T-TH in a not inconsiderable percentage of the cases examined in various studies. In Monteiro s work, unilateral pain was present in 18.7% of the T-TH cases (15), while the figure for unilaterality in T-TH in Rasmussen s work was 10% (16). Throbbing has been observed usually in ca 60% of T-TH patients (21), a value higher than that found in migraine patients (ca 51%) observed by the same group (23). After all, throbbing is an inherent trait of MwoA, not of T-TH. Also in the present series, a certain percentage had throbbing; this may, in our cases, be due to a minor pollution, possibly from MwoA. The T-TH criteria, nevertheless, were fulfilled in our cases. For this reason, these cases were categorised as T-TH cases and not as non-classifiable ones, a group that in Vågå contained 136 individuals, or 7.4%. Coarse structural changes, observed for example on MRI, have not been verified in CEH (24). Remarkably, in the present study, there were major differences between T-TH/MwoA, on the one hand, and CEH on the other hand, with regard to cardinal CEH variables. Such variables include: ipsilateral shoulder and diffuse/radicular arm pain; range of motion in the neck, and onset of pain in the neck/posterior part of the head. Incidentally, this pattern corresponded well to the pain drawings done by CEH patients in another context (25). Even larger differences were found in relation to the mechanical precipitation of attacks. The relative lack of migrainous traits is pretty similar in T-TH and CEH (Table II). Moreover, the age at onset was clearly different in T-TH/MwoA compared to CEH, the difference being most marked as regards MwoA (Table I). Although the latter feature cannot be used diagnostically in the solitary case, this feature too may indicate differences in pathogenesis. Validation The tendency reported in our previous communications from the Vågå study seemed to be present in this study, too: a constellation of symptoms and signs set forth in a written format, stemming from a solitary individual, can more easily lead to repeated, similar interpretation than a repeated questioning of that individual. An appreciable interval between two questionings may enhance this tendency. A more than minor change in headache degree may lead to a change of headache category; thus, in the present validation: from zero headache to mild Functional Neurology 2008; 23(2):

6 O. Sjaastad et al. T-TH; and from T-TH to possible MwoA (Table IV, cases E&D). Such a change is probably not less understandable than the change taking place from day 1 to day 3 in a solitary migraine attack. If one were confronted directly with a patient on the third day of the attack, without any information on what the situation had been like 1-2 days earlier, one would, not infrequently, find it very difficult to arrive at a correct categorisation; the late headache phase is, nevertheless, still part of a migraine attack. Also, the amelioration with age in Bille s (26) childhood migraine patients fits in with this view. The level of concurrence between examinations I and II in the six T-TH patients among the 41 re-examined individuals, is among the lowest recorded in the entire Vågå study. Concluding remarks A minor change in, or a wrong assessment of, intensity may lead to a change in headache category. It may be too easy just to push a case into the T-TH category. It is our considered opinion that the IHS T-TH criteria, weak as they may be, should be followed strictly, now and for the foreseeable future. The finding that, generally, CEH attacks (but generally not attacks of T-TH/MwoA) start posteriorly, combined with the fact that exacerbations can be provoked mechanically from the neck in CEH, may seem to be crucial factors in distinguishing CEH from T-TH/MwoA, clinically. These major and systematic differences indicate that these disorders have a different nature: T-TH/MwoA are unlikely to be CEH variants. Equally, CEH is unlikely to be a T-TH or a MwoA variant. References 11. Ad Hoc Committee on Classification of Headache. Classification of headache. JAMA 1962;179: Heyck HS. Headache and Facial Pain. Stuttgart; Thieme Verlag Headache Classification Committee of the International Headache Society. Classification and diagnostic criteria for headache disorders, cranial neuralgias and facial pain. Cephalalgia 1988;8(Suppl 7): Headache Classification Subcommittee of the International Headache Society. The International Classification of Headache Disorders: 2nd edition. Cephalalgia 2004;24 (Suppl 1): Merskey H, Bogduk N. Classification of Chronic Pain. 2nd edn. Seattle WA; IASP Press Sjaastad O, Båtnes J, Haugen S. The Vågå study; an outline of the design. Cephalalgia 1999;19(Suppl 25): Sjaastad O, Pettersen H, Bakketeig LS. The Vågå Study; epidemiology of headache. I. The prevalence of ultrashort paroxysms. Cephalalgia 2001;21: Sjaastad O, Fredriksen TA, Petersen HC, Bakketeig LS. Grading of headache intensity. A proposal. J Headache Pain 2002;3: Sjaastad O, Fredriksen TA, Petersen HC, Bakketeig L. Features indicative of cervical abnormality. A factor to be reckoned with in clinical headache work and research? Funct Neurol 2003;18: Sjaastad O, Bakketeig LS. Skin-fold thickness and reproducibility of the skin-roll test. Vågå study. J Headache Pain 2003;4: Sjaastad O, Fredriksen TA, Pfaffenrath V. Cervicogenic headache: diagnostic criteria. Headache 1990;30: Sjaastad O, Fredriksen TA, Pfaffenrath V. Cervicogenic headache: diagnostic criteria. The Cervicogenic Headache International Study Group. Headache 1998;38: Raskin NH, Schwartz RK. Icepick-like pain. Neurology 1980;30: Lance JW. Mechanisms and Management of Headache. 5th edn. London; Butterworth/Heinemann Monteiro JP. Cefaleias. Estudo epidemiologico e clinico de uma população urbana. Thesis. Porto, Rasmussen BK. Epidemiology of headache. Cephalalgia 1995;15: Rasmussen BK. Epidemiology of headache. Thesis. Copenhagen University Sjaastad O, Bakketeig LS, Petersen HC. Migraine with aura: visual disturbances and interrelationship with the pain phase. Vågå study of headache epidemiology. J Headache Pain 2006;7: Sjaastad O. Bakketeig LS. Prevalence of cervicogenic headache. Vågå study of headache epidemiology. Acta Neurol Scand 2008;117: Sjaastad O, Wang H, Bakketeig LS. Neck pain and associated head pain: persistent neck complaint with subsequent, transient, posterior headache. Acta Neurol Scand 2006;114: Lavados PM, Tenhamm E. Epidemiology of tension-type headache in Santiago, Chile: a prevalence study. Cephalalgia 1998;18: Nappi G, Manzoni GC. Manuale delle cefalee. Milan; Masson Lavados PM, Tenhamm E. Epidemiology of migraine headache in Santiago, Chile: a prevalence study. Cephalalgia 1997;17: Inan N, Yilmaz G, Surer H et al. Is there a role for nitric oxide activity in cervicogenic headache? Funct Neurol 2007; 22: Drottning M, Staff P, Sjaastad O. Cervicogenic headache (CEH) six years after whiplash injury. Funct Neurol 2007; 22: Bille B. Migraine in childhood and its prognosis. Cephalalgia 1981;1: Functional Neurology 2008; 23(2): 71-76