Testing the diagnostic criteria of tension-type headache

Tension-type headache (TTH) is the most prevalent (1), but also least studied primary headache worldwide. 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). Fieldtesting 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