Testing of diagnosis criteria of tension-type headache: A multicenter clinical study

Abstract

Objective

Tension-type headache is

*These authors contributed equally to this work.

usually manifested as head pain without associated symptoms, and the validation of diagnostic criteria presented are lacking and highly required in the International Classification of Headache Disorders. The aim of the present study was to explore the diagnosis criteria of tension-type headache in a multicenter-based sample from Chongqing, China.

Methods

Clinical characteristics and demographics were systematically and prospectively collected between March 2014 and December 2015 from 15 participating hospitals in Chongqing, using a semi-structured face-to-face interview. All patients were asked to complete a headache diary for at least 4 weeks.

Results

Out of 1832 patients with headache, 150 patients (97 female/53 male, 44.56 ± 11.9 years old) were diagnosed with tension-type headache based on the standard International Classification of Headache Disorders, 3rd edition beta version, and interestingly, 114 (76%) patients were diagnosed with tension-type headache based on the alternative criteria. One patient was excluded because only two of the four characteristics were fulfilled. Thirty-five (23.3%) patients did not meet the alternative criteria because of associated symptoms, including mild nausea (n = 6), photophobia (n = 1), and phonophobia (n = 28). All patients with TTH had mild or moderate headaches, 98.0% of patients suffered from non-pulsating headaches, 99.3% of patients said their headaches were not aggravated by routine physical activity, and 77.3% of patients had bilateral headache.

Conclusions

Non-pulsating headaches and headaches that are not aggravated by routine physical activity may represent core criteria for screening patients with tension-type headache. Nausea might not be an exclusion feature for diagnosis of TTH, but an important criterion for screening. Further studies are needed.

Keywords

Clinical characteristics diagnostic criteria associated symptoms

Introduction

Tension-type headache (TTH) is the most prevalent primary headache disorder, occurring in 20–60% of the general population (1,2). The costs associated with treating TTH are higher than for migraine, because more people suffer from TTH (1). Decreased work efficiency and reduced social activity are reported by up to 60% of TTH patients (3). However, the accurate diagnosis of TTH has received limited attention over the last few decades.

TTH is characterized by nothing more than a pain in the head (4). The definition depends exclusively on clinical symptoms, which can be found in other headache types such as migraine (5,6). In fact, these headaches are often distinguished by difference of clinical features based on the International Classification of Headache Disorders, 3rd edition beta version (ICHD-3 beta) (7).

Further diagnostic criteria for TTH (which we have called alternative criteria) have been proposed to exclude migraine that phenotypically resembles TTH according to ICHD-3 beta criteria. The alternative criteria define a more specific core TTH syndrome, but have not been well tested (8).

We surveyed successive TTH patients attending neurological clinics from 15 hospitals in China to explore the clinical characteristics and diagnosis.

Methods

Patients and clinical setting

This multicenter clinical study was performed at 15 participating hospitals in Chongqing, China. We prospectively enrolled consecutive patients diagnosed with TTH from March 2014 to December 2015 in neurological clinics. The TTH diagnosis was based on the ICHD-3 beta criteria for infrequent episodic tension-type headache (iETTH) and frequent episodic tension-type headache (fETTH) (codes 2.1 and 2.2) and chronic tension-type headache (CTTH) (code 2.3), using a semi-structured face-to-face interview as described previously (9).

Participating neurologists were trained by headache specialist Jiying Zhou in the lead headache clinic. A pioneer trial was conducted in the first month. All enrolled patients were followed up by three neurologists (Xueying Kong, Jinjin Chen, and Huahua Jiang) in the lead headache clinic. Headache characteristics (position, property, duration, intensity, aggravation after physical activity, associated symptoms, etc.) were validated by telephone interview. In addition, medical records were reviewed every week to verify the diagnosis. If the diagnosis was contentious, Jiying Zhou decided the final diagnosis after telephone interview with the patient. Two medium-term meetings were held to conclude the progress of the project and to solve problems that arose in January and August 2015. In the latter part of the study, Xueying Kong and Jinjin Chen from the lead clinic collected and analyzed the data.

Inclusion criteria were for subjects to be between 18–65 years of age, have a TTH diagnosis based on ICHD-3 beta criteria, headache more than 1 year, and the ability to complete a headache diary. Exclusion criteria were an International Headache Society diagnosis of medication-overuse headache (MOH), current or planned pregnancy or breastfeeding, migraine headache for more than 1 day a month, serious somatic or psychiatric illnesses, other pain disorder (e.g. arthritis) requiring analgesic treatment, and failure to complete baseline diary recordings of headache activity and medication use.

Patients presenting at the participating clinics with headache were interviewed. Participating neurologists conducted detailed interviews to determine the demographic and socioeconomic characteristics, headache features, triggers, family history of headache, mood disturbances, Hospital Anxiety and Depression Scale (HADS), and Headache Impact Test (HIT-6). In addition, neurologists performed manual palpation (pressure pain examinations) in each patient in seven locations including frontal muscle, masseter muscle, temporal muscle, alary muscle, sternocleidomastoid muscle, trapezius muscle, and splenius cervicis muscle (10). Symmetrical muscles were palpated simultaneously followed by unilateral palpation to allow for accurate side-to-side comparison.

After their first visit, all enrolled patients received a headache diary and were told to record headache characteristics, including type and amount of medication used for at least 4 weeks (11). Headache frequency, intensity, associated symptoms, and medication consumption at the time of the initial consultation were recorded as baseline values. The headache diary was examined and verified to exclude probable migraine.

The study was approved by the local ethics board and informed consent was obtained from all participants.

Follow-up response

The baseline assessment included 1 month of headache recording. Afterwards, patients were generally treated empirically with amitriptyline (25–50 mg per day), Chinese medicine (Yangxue Qingnao Granule, 12 g per day) (12), or a combination of both based on doctors’ judgements and patients’ preferences. Seven patients received lifestyle adjustments as treatments due to low frequency of headaches. Patients recorded all headaches in a daily headache diary.

Data processing and statistical analysis

Statistical analysis was performed using SPSS software, version 20.0 (Chicago, IL, USA). Patients that fulfilled ICHD-3 standard criteria for ETTH and CTTH were tested for alternative criteria listed in the alternative of ICHD-3 beta (code A2). Continuous variables are presented as means ± SD, and Student’s t-test was used to evaluate differences between the two groups. Categorical variables are presented as frequency distributions (N, %), and Chi-square or Fisher’s exact test was executed where applicable. Signiﬁcance was set at p ≤ 0.05 for all statistical tests.

Results

A total of 13,537 patients visited the participating neurological clinics and 1832 headache patients were screened during the study period. Of these, 397 patients with tension-type-like headaches were selected for further screening. Twenty-eight patients were excluded based on a diagnosis of secondary headache. The remaining 271 patients were diagnosed with TTH according to ICHD-3 criteria. Among them, 94 (34.7%) patients were excluded after recording migraine or probable migraine (PM) symptoms in their headache diary during screening. An additional 27 (10.0%) patients dropped out. In the end, 150 (55.3%) patients were enrolled in the study (Figure 1).

Figure 1.

Flowchart of patients and diagnoses during the run-in period.

Demographics and clinical characteristics of fETTH and CTTH by ICHD-3β standard criteria

A total of 150 patients diagnosed with TTH were finally included. Sixty-six (44.0%) were classified as fETTH, and 84 (56%) were classified as CTTH (Table 1). None of the enrolled patients is iETTH. More female patients were diagnosed with fETTH (63.6%) and CTTH (65.5%) than males. The overall sex prevalence ratio was 1.83. Patients with CTTH were prone to have a lower education level compared to patients with fETTH. The average number of days with headache per month was 5.89 (SD 3.68) in fETTH patients and 25.42 (SD 6.22) in CTTH patients. Patients with fETTH had a mean headache pain intensity of 3.88 (SD 1.28) and CTTH patients of 3.95 (SD 1.23) based on a Visual Analogue Scale.

Table 1.

Demographics and clinical features of fETTH and CTTH.

	fETTH (n = 66)	CTTH (n = 84)	p value
Age, mean ± SD	42.88 ± 12.09	45.88 ± 11.66	0.127
Gender, n (%)			0.815
Female	42 (63.6)	55 (65.5)
Male	24 (36.4)	29 (34.5)
Married (%)	59 (89.4)	77 (91.7)	0.635
Educational level, n (%)			0.037*
< high school	28 (42.4)	50 (59.5)
≥ high school	38 (57.6)	34 (40.5)
BMI, mean ± SD	23.66 ± 4.57	23.24 ± 2.78	0.509
Alcohol, n (%)	3 (4.5)	2 (2.4)	0.783
Smoker, n (%)	6 (9.1)	6 (6.4)	0.737
Age at onset, mean ± SD	35.33 ± 12.90	37.02 ± 10.78	0.589
Courses of headache, mean ± SD	8.60 ± 8.73	9.09 ± 8.78	0.736
Pain intensity, mean ± SD	3.88 ± 1.28	3.95 ± 1.23	0.722
Average headache days per month, mean ± SD	5.89 ± 3.68	25.42 ± 6.22	0.000*
Duration of headache			0.000*
0.5–4 hours	29 (43.9)	25 (29.8)
4–72 hours	37 (56.1)	37 (44.0)
3–7 days	0 (0.0)	22 (26.2)
Current acute use of analgesics, n (%)	23 (34.8)	40 (47.6)	0.116
Category of used analgesics, n (%)			0.065
Single analgesics	3 (13.0)	6 (15.0)
Combination analgesics	9 (39.1)	26 (65.0)
Multiple analgesics	11 (47.9)	8 (20.0)
Family headache History, n (%)	32 (48.5)	23 (27.4)	0.008*
Pressure pain	22 (33.3)	28 (33.3)	1.000
Sleep disturbance	30 (45.5)	47 (56.0)	0.202
HIT-6, mean ± SD	50.64 ± 8.00	52.92 ± 7.91	0.190
HADS/A, mean ± SD	6.17 ± 2.76	6.24 ± 4.07	0.927
HADS/D, mean ± SD	4.69 ± 3.08	4.44 ± 3.76	0.738

fETTH: frequent episodic tension-type headache; CTTH: chronic tension-type headache; BMI: Body Mass Index; HIT-6: Headache Impact Test; HADS: Hospital Anxiety and Depression Scale. Note: *p ≤ 0.05.

CTTH patients were more likely to be older, female, have a lower educational level, use more analgesics, and suffer from sleep disturbance than fETTH patients (Table 1). The overall mean time of headache duration was significantly longer for CTTH patients than fETTH patients.

Notably, 33% of CTTH patients had muscle pressure pain (Table 1). The same was reported by patients with fETTH. Muscle tenderness had no relationship with headache intensity, course of headache, and headache frequency.

In the 150 TTH patients, the quality of the headache was described as pressing (46%) and dull pain (19%). Tightening pain was reported by 11% of patients, whereas pulsating pain was described by 2% of patients. Stabbing pain appeared in 1% of patients, 18% of patients suffered headache of more than one quality, and 3% of patients accounted to another headache quality that is hard to define.

Testing of the TTH standard and alternative criteria of the ICHD-3 beta

The 150 patients diagnosed with TTH based on ICHD-3 standard criteria were re-diagnosed using alternative criteria. Based on this re-diagnosis, 114 (76%) patients were diagnosed with TTH (Table 2).

Table 2.

Diagnostic features of TTH according to standard and alternative criteria.

	Standard criteria (n = 150)		Alternative criteria (n = 114)
	ETTH (n = 66)	CTTH (n = 84)	ETTH (n = 49)	CTTH (n = 65)	p value
Bilateral location	45 (68.2)	71 (84.5)	35 (71.4)	53 (81.50)	0.064
Non-pulsating quality	65 (98.5)	82 (97.6)	48 (98.0)	65 (100.0)	0.489
Mild or moderate intensity	66 (100.0)	84 (100.0)	49 (100.0)	65 (100.0)	1.000
Not aggravated by routine physical activity	65 (98.5)	84 (100.0)	48 (98.0)	65 (100.0)	0.335
Mild nausea	0 (0.0)	6 (7.1)	0 (0.0)	0 (0.0)	0.003*
Photophobia	0 (0.0)	1 (1.2)	0 (0.0)	0 (0.0)	0.513
Phonophobia	17 (25.8)	11 (13.1)	0 (0.0)	0 (0.0)	0.000*

Note: *p ≤ 0.05.

The differences in criteria were the headache characteristics and the associated symptoms. One patient was excluded because only two of the four characteristics were fulfilled. The other 35 patients were excluded because of associated symptoms, including mild nausea (n = 6), photophobia (n = 1), and phonophobia (n = 28).

All patients with TTH had mild or moderate headaches, 98.0% (147of 150) suffered from non-pulsating headaches, 99.3% (149 of 150) said their headaches were not aggravated by routine physical activity, and 77.3% (116 of 150) had bilateral headache, according to standard criteria. There was no difference between patients with fETTH and those with CTTH in terms of headache features.

Socio-demographic characteristics of TTH patients according to standard and alternative criteria

The distribution of age, gender, marriage status, educational level, and body mass index (BMI) was not significantly different in TTH patients diagnosed using standard and alternative criteria (Table 3).

Table 3.

Socio-demographic distribution of patients diagnosed with tension-type headache based on standard and alternative criteria.

	Standard criteria (n = 150)	Alternative criteria (n = 114)	p value
Age, mean ± SD	44.56 ± 11.90	44.11 ± 11.84	0.758
Gender, n (%)			0.586
Female	97 (64.7)	70 (61.4)
Male	53 (35.3)	44 (38.6)
BMI, mean ± SD	23.44 ± 3.70	23.47 ± 3.89	0.950
Educational level, n (%)			0.968
<high school	78 (52.0)	59 (51.8)
≥high school	72 (48.0)	55 (48.2)
Married (%)	136 (90.7)	105 (92.1)	0.681
Alcohol (%)	5 (3.3)	5 (4.4)	0.906
Smoker (%)	12 (8.0)	10 (9.6)	0.653
Current acute use of analgesics, n (%)	63 (42.0)	43 (37.7)	0.482
Category of used analgesics, n (%)			0.999
Single analgesics	9 (14.2)	6 (14.0)
Combination analgesics	35 (55.6)	24 (55.8)
Multiple analgesics	19 (30.2)	13 (30.2)
Family headache history, n (%)	55 (36.7)	45 (39.5)	0.641
Sleep disturbance	78 (52.0)	62 (54.4)	0.700
HIT (mean ± SD)	52.12 ± 7.97	51.47 ± 7.28	0.593
HADS/A (mean ± SD)	6.22 ± 3.63	6.11 ± 3.44	0.841
HADS/D (mean ± SD)	4.53 ± 3.52	4.32 ± 3.26	0.695
Significant remission to amitriptyline	32 (59.3)	24 (64.9)	0.664

Follow-up response

One hundred and forty-three patients received medication. The overall response rate was 71.3% (n = 107, 68 females, 39 males), including telephone and face-to-face interviews. The main reasons for lack of follow-up were patient refusal and changed telephone number. Age, gender, HIT scores, and HADS scores did not differ between participants and non-participants.

The median follow-up time was 5 months (range: 1–12 months). Three patients had a migraine-like combined headache less than 1 day a month. None of the other patients have reported a migraine or other type of headache to date.

Discussion

The validation of diagnostic criteria presented in the ICHD are lacking and highly needed in TTH. We therefore evaluated the standard criteria and alternative criteria of ICHD-3 beta to explore the socio-demographic, clinical characteristics, and follow-up response between the two groups. No significant difference was found except the associated symptoms, such as nausea and phonophobia.

In this multicenter study, we classified all patients with ETTH and CTTH. Indeed, all ETTH patients had at least two headache days per month, another way of saying they were fETTH. On the whole, there were more female TTH patients than males in this study, in agreement with previous studies (13,14). We also observed a strong association between TTH prevalence and education; prevalence increased with education level in fETTH patients, but declined with increasing education level in CTTH patients.

Throbbing/pulsating pain was one of the most prominent migrainous features. The frequency of pulsating pain for TTH in previous studies has varied from 17.5% to 59.9% (5,8,15). Notably, 2% of TTH patients had a pulsating headache in our survey. This wide range of difference was most likely due to various classification criteria of TTH, or inclusion criteria of study groups. Pulsating pain might not be an exclusion feature for diagnosis of TTH, but is an important criterion for screening.

The ICHD-3 diagnostic criteria include shorter duration headaches. There were differences in the duration of headache attacks between fETTH and CTTH patients. CTTH headaches were longer than fETTH headaches. In addition, 74 patients (49.3%) had headaches lasting 4–72 hours, which overlaps with the criteria for migraine. This may make it difficult to distinguish migraine from TTH.

The etiology of TTH is thought to be muscular and pericranial muscle tenderness, which is a unique feature of TTH (16). A previous study in Denmark indicated that 77% of adults with CTTH, and 37% of those with ETTH, had muscle tenderness, investigated on manual palpation only (10). In our study, 33% of patients with CTTH and fETTH had muscle pressure pain. Methodological differences and differences between study populations might explain the discrepancy between these results. Several lines of evidence had revealed that migraine was accompanied by muscle tension or neck pain (17 –20). Based on these findings, pericranial muscle tenderness may not be a good criterion for distinguishing between TTH and migraine.

Our study showed a family history of headache in 48.5% of fETTH patients and 27.4% of CTTH patients, in agreement with previous studies (21). This might be attributed to the high prevalence of infrequent and frequent ETTH (22,23). A twin study of ETTH showed that environmental influences were predominantly responsible for ETTH and that genetics had little or no influence (24).

Migraine and TTH were best distinguished by aggravation of pain following routine physical activity. This criterion was more indicative than unilaterality or pulsating quality. Diagnosis of TTH is currently based on the patient’s evaluation of the headache characteristics, because biomarkers or definitive headache features are lacking (25). In our survey, all patients fulfilled three of the four alternative criteria, which are proposed to be more specific than standard criteria. Furthermore, almost all patients reported that their headaches were not aggravated by routine physical activity. In contrast, a Korean study showed that 81.2% of patients fulfill three of the four characteristics (8). The differences might be explained by stricter inclusion criteria and baseline headache recordings, or by different study samples.

Previous studies showed that a minority of patients fulfilled the diagnostic criteria of CM and CTTH (26,27). That was possible when two of the four pain characteristics were present and headaches were associated with mild nausea (28). Therefore, associated symptoms are important for distinguishing between migraine and TTH. For CTTH to be diagnosed, mild nausea, photophobia, or phonophobia may be present. For ETTH diagnosis, photophobia or phonophobia can be present. The majority of TTH patients in this study were diagnosed according to standard criteria, but the missing alternative criteria were due to associated symptoms, such as mild nausea (4.0%), photophobia (0.6%) and phonophobia (18.7%). In conclusion, our findings indicate that three of the four headache characteristics did not reduce the diagnostic sensitivity. However, mild nausea was only present in CTTH (4.0%), and 19.3% of patients had photophobia or phonophobia in our study, therefore further studies are needed to verify the benefits and risks of removing the associated symptoms, and the application the alternative TTH diagnosis criteria.

Distinguishing between migraine/PM and TTH based on ICHD-3 criteria is complicated because each headache type has characteristics of the other. Non-pulsating headaches and headaches that were not aggravated by routine physical activity were present in almost all TTH patients. These may represent useful diagnostic criteria for TTH screening, thereby avoiding over-diagnosis caused by a lack of distinctive TTH features. However, in early reports, pain was shown to be aggravated by physical activity in 21.1–31.8% of TTH suffers (5,15,20). The explanation for the difference in distribution may be the progression of knowledge of TTH.

There are some limitations to be considered. This study was clinic-based and the data cannot estimate the prevalence of TTH in the general population. The findings require further study and cannot be extrapolated to the general population directly. Furthermore, the intermediate headache status was not compared between baseline and follow-up, so the precise course of the headaches was not clarified. Another limitation is that the strict inclusion criteria make it impossible to calculate the sensitivity and specificity of the criteria and might narrow the range of patients included.

In summary, this study provided the clinical features and first testing of TTH in a multi-center study in China. TTH was female predominant, with an onset at middle age. A mild or moderate headache intensity was the core symptom of TTH. Non-pulsating headaches and headaches that are not aggravated by routine physical activity might represent important means of identification for screening patients with headache. Fulfilling three of the four headache characteristics in the alternative criteria did not reduce the diagnostic sensitivity, but further studies are needed to verify the benefits and risks of removing the associated symptoms, and the application the alternative TTH diagnosis criteria.

Clinical implications

This study details the clinical characteristics of TTH. TTH predominantly occurs in middle-aged women. CTTH patients are mainly older, female, have a lower education level, use more analgesics, and suffer more from sleep disturbance compared with fETTH patients.

Non-pulsating headaches and headaches that are not aggravated by routine physical activity may represent important means of identification for screening patients with headache.

Footnotes

Acknowledgement

We thank all the physicians. Without their meticulous follow-up, this study could not have been completed. We apologize for not being able to list all the names of physicians who participated in the study owing to limited space. We also thank the chief investigators of each institute.

The authors thank the research support from Tasly Pharm Company.

Declaration of conflicting interests

The authors declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Funding

The authors received no financial support for the research, authorship, and/or publication of this article.

References

Stovner

Hagen

Jensen

et al.

The global burden of headache: A documentation of headache prevalence and disability worldwide. Cephalalgia 2007; 27: 193–210.

Crystal

Robbins

. Epidemiology of tension-type headache. Curr Pain Headache Rep 2010; 14: 449–454.

Bendtsen

Jensen

. Tension-type headache: The most common, but also the most neglected, headache disorder. Curr Opin Neurol 2006; 19: 305–309.

Crystal

Robbins

. Tension-type headache mimics. Curr Pain Headache Rep 2011; 15: 459–466.

Rasmussen

Jensen

Olesen

. A population-based analysis of the diagnostic criteria of the International Headache Society. Cephalalgia 1991; 11: 129–134.

Turkdogan

Cagirici

Soylemez

et al.

Characteristic and overlapping features of migraine and tension-type headache. Headache 2006; 46: 461–468.

Headache Classification Committee of the International Headache Society. The International Classification of Headache Disorders, 3rd edition (beta version). Cephalalgia 2013; 33: 629–808.

Chu

Cho

Kim

et al.

Field testing the alternative criteria for tension-type headache proposed in the third beta edition of the international classification of headache disorders: Results from the Korean headache-sleep study. J Headache Pain 2014; 15: 28–28.

Wang

Huang

et al.

Triggers of migraine and tension-type headache in China: A clinic-based survey. Eur J Neurol 2013; 20: 689–696.

10.

Jensen

Rasmussen

. Muscular disorders in tension-type headache. Cephalalgia 1996; 16: 97–103.

11.

Russell

Rasmussen

Brennum

et al.

Presentation of a new instrument: The diagnostic headache diary. Cephalalgia 1992; 12: 369–374.

12.

Liao

Yan

et al.

Effects of Yangxue Qingnao Granules on chronic cerebral circulation insufficiency: A randomized, double-blind, double-dummy, controlled multicentre trial. Psychogeriatrics 2013; 13: 29–34.

13.

Schwartz

Stewart

Simon

et al.

Epidemiology of tension-type headache. JAMA 1998; 279: 381–383.

14.

Lyngberg

Rasmussen

Jorgensen

et al.

Has the prevalence of migraine and tension-type headache changed over a 12-year period? A Danish population survey. Eur J Epidemiol 2005; 20: 243–249.

15.

Ashina

Lyngberg

Jensen

. Headache characteristics and chronification of migraine and tension-type headache: A population-based study. Cephalalgia 2010; 30: 943–952.

16.

Olesen

. Clinical and pathophysiological observations in migraine and tension-type headache explained by integration of vascular, supraspinal and myofascial inputs. Pain 1991; 46: 125–132.

17.

Jensen

Rasmussen

Pedersen

et al.

Cephalic muscle tenderness and pressure pain threshold in a general population. Pain 1992; 48: 197–203.

18.

Jensen

Rasmussen

Pedersen

et al.

Muscle tenderness and pressure pain thresholds in headache. A population study. Pain 1993; 52: 193–199.

19.

Tfelt-Hansen

Lous

Olesen

. Prevalence and significance of muscle tenderness during common migraine attacks. Headache 1981; 21: 49–54.

20.

Selby

Lance

. Observations on 500 cases of migraine and allied vascular headache. J Neurol Neurosurg Psychiatry 1960; 23: 23–32.

21.

Friedman

Von Storch

Merritt

. Migraine and tension headaches; a clinical study of two thousand cases. Neurology 1954; 4: 773–788.

22.

Russell

. Tension-type headache in 40-year-olds: A Danish population-based sample of 4000. J Headache Pain 2005; 6: 441–447.

23.

Russell

Levi

Saltyte-Benth

et al.

Tension-type headache in adolescents and adults: A population based study of 33,764 twins. Eur J Epidemiol 2006; 21: 153–160.

24.

Ulrich

Gervil

Olesen

. The relative influence of environment and genes in episodic tension-type headache. Neurology 2004; 62: 2065–2069.

25.

Fumal

Schoenen

. Tension-type headache: Current research and clinical management. Lancet Neurol 2008; 7: 70–83.

26.

Mongini

Deregibus

Raviola

et al.

Confirmation of the distinction between chronic migraine and chronic tension-type headache by the McGill Pain Questionnaire. Headache 2003; 43: 867–877.

27.

Lipton

Cady

Stewart

et al.

Diagnostic lessons from the spectrum study. Neurology 2002; 58: S27–S31.

28.

Silberstein SD, Olesen J, Bousser MG, et al. The International Classification of Headache Disorders, 2nd Edition (ICHD-II) – revision of criteria for 8.2 Medication-overuse headache. Cephalalgia 2005; 25: 460–465.