Testing the diagnostic criteria of tension-type headache

Tension-type headache (TTH) is the most prevalent (1), but also least studied primary headache world-wide. TTH varies considerably in frequency, duration and severity, which implies that all TTH subjects do not fit into a homogenous group (2). It is often expressed that both patients and clinicians are challenged by differentiating TTH headache episodes from migraine headache episodes, which has resulted in the hypothesis that both headache disorders are at each end of a migraine continuum (3,4), a hypothesis which remains to be supported by clear clinical and scientific data. As an example, population-based studies have shown no significant differences in prevalence of TTH in subjects with or without migraine (5,6), even though TTH episodes are more pronounced and severe in migraineurs (6).

In a present study, “Testing of diagnosis criteria of tension-type headache: A multicenter clinical study”, Kong et al. (7) included 150 patients with almost pure TTH from different neurological clinics in China; 44 % were classified as frequent episodic TTH and 56% chronic TTH. The TTH patients were then re-diagnosed using the A2 TTH alternative criteria from the International Classification of Headache Disorders third edition (ICHD-3) appendix (8), which resulted in 114 of the 150 patients (76%) being diagnosed with TTH (7). Interestingly, only one of the 36 excluded patients were due to lack of fulfillment of three out of four of the C criteria (8), while the remainder were due primarily to 28 (78%) having phonophobia, six (17%) having mild nausea and one having photophobia (7). The authors should be congratulated for a clear and well described study, which is very interesting and highly needed for exploring the A2 TTH alternative criteria.

The A2 TTH alternative criteria were proposed in the hope of excluding migraine that phenotypically resembles tension-type headache, which was suggested to increase specificity, but at the same time, reduce the sensitivity of the criteria, resulting in a larger proportion of patients whose headaches could be classified only as 2.4 Probable tension-type headache or 1.5 Probable migraine (8). The Kong et al. study (7) shows that in this clinic-based population, the A2 TTH alternative C criteria does not lower sensitivity – it is the associated symptoms, primarily phonophobia, that lower the sensitivity (7). This necessarily raises the question of whether accompanying symptoms like phonophobia are migraine-specific. In cluster headache, phonophobia or photophobia was reported by 73% of patients, with no significant differences regarding patients with and without comorbid migraine (9). In 139 idiopathic intracranial hypertension patients with headache, 70% had photophobia and 52% phonophobia (10) and in 100 patients with acute post traumatic headache, nausea and photophobia and/or phonophobia were present in 42% and 55% of the patients (11). In complex regional pain syndrome patients, 38% reported hyperacusis, which was associated with allodynia/hyperalgesia and with more affected extremities (12). Thus, associated symptoms are not unusual in other headache and pain conditions than migraine, which also questions the soundness of totally excluding the occurrence of mild nausea, phonophobia or photophobia in TTH.

It also is important to emphasize that the Kong et al. study (7) cannot be considered a genuine field-testing study, which the authors also acknowledge, as it is a relatively small clinic-based sample that only included selected patients with primarily pure TTH (7). Field-testing studies in primary headaches should be population-based for the ICHD-3 to be useful in the general population. In comparison, Chu et al. (13) performed a field-testing study in a population-based sample of 585 people with TTH according to the ICHD-3 criteria and found that only 41% of these fulfilled the A2 TTH alternative criteria (13), out of which 55% had phonophobia, 14% photophobia, 31% did not fulfill three out of four of the C criteria, and none had nausea. The large difference in symptoms between the two studies highlights the selection differences and need for large population-based samples when performing field testing on primary headaches. Given that the Chu et al. study (13) estimated a prevalence of 21% in South Korea, applying the alternative TTH criteria into the ICHD main body would result in more than one million headache subjects in South Korea alone being classified as having probable migraine or probable TTH. Thus, applying the TTH alternative criteria leads to a very substantial number of subjects without a definite headache diagnosis, which necessarily raises many challenges in headache research as well as in treatment and medical reimbursement. It is very doubtful that patients with probable tension-type headache or probable migraine would be an obvious target for scientific exploration and drug development. In addition, there seem to be a fair stability of confirmed migraine and TTH over time, whereas stability of probable migraine and TTH diagnosis is considerably lower (14).

In conclusion, the Kong et al. study (7) shows that in selected clinic-based samples the A2 TTH alternative criteria lower the sensitivity, and thereby exclude one out of four patients due to primarily associated symptoms. It is highly admirable of Kong and co-workers to carry out this type of validation study. Whether the TTH alternative criteria are necessary and represent a meaningful distinction in headache classification needs to be shown by demonstrating that there are pathophysiological differences between patients that fulfill the present ICHD-3 TTH criteria compared to TTH patients only fulfilling the alternative criteria. Lowering the sensitivity of the most prevalent primary headache needs to be considered very carefully, as it will result in millions of headache sufferers being left with probable headache diagnosis entities.