2. Tension-type headache

Previously used terms:
Tension headache; muscle contraction headache; psychomyogenic headache; stress headache; ordinary headache; essential headache; idiopathic headache; psychogenic headache.

Coded elsewhere:
Tension-type-like headache attributed to another disorder is coded to that disorder.

General comment
Primary or secondary headache or both?
When a headache with the characteristics of tension-type characteristics occurs for the first time in close temporal relation to another disorder that is a known to cause headache, or fulfils other criteria for causation by that disorder, the new headache is coded as a secondary headache attributed to the causative disorder. When pre-existing tension-type headache becomes chronic in close temporal relation to such a causative disorder, both the initial tension-type headache diagnosis and the secondary diagnosis should be given. When pre-existing tension-type headache is made significantly worse (usually meaning a two-fold or greater increase in frequency and/or severity) in close temporal relation to such a causative disorder, both the initial tension-type headache diagnosis and the secondary diagnosis should be given, provided that there is good evidence that the disorder can cause headache. In the case of chronic tension-type headache with medication overuse, a close temporal relation is often difficult to establish. Therefore, both diagnoses, 2.3 Chronic tension-type headache and 8.2 Medication-overuse headache, should be given in all such cases.

Introduction
2. Tension-type headache is very common, with a lifetime prevalence in the general population ranging between 30% and 78% in different studies, and it has a very high socio-economic impact.

Whilst this type of headache was previously considered to be primarily psychogenic, a number of studies have appeared after publication of ICHD-I that strongly suggest a neurobiological basis, at least for the more severe subtypes of tension-type headache.

The division of 2. Tension-type headache into episodic and chronic subtypes, which was introduced in ICHD-I, has proved extremely useful. In ICHD-II, the episodic form was further subdivided into an infrequent subform with headache episodes less than once per month and a frequent subform. 2.3 Chronic tension-type headache is a serious disease, causing greatly decreased quality of life and high disability. 2.2 Frequent episodic tension-type headache can be associated with considerable disability, and sometimes warrants treatment with expensive drugs. In contrast, 2.1 Infrequent episodic tension-type headache, which occurs in almost the entire population, usually has very little impact on the individual and, in most instances, requires no attention from the medical profession. The distinction of 2.1 Infrequent episodic tension-type headache from 2.2 Frequent episodic tension-type headache thus separates individuals who typically do not require medical management, and avoids categorizing almost the entire population as having a significant headache disorder, yet allows their headaches to be classified.

The exact mechanisms of 2. Tension-type headache are not known. Peripheral pain mechanisms are most likely to play a role in 2.1 Infrequent episodic tension-type headache and 2.2 Frequent episodic tension-type headache, whereas central pain mechanisms play a more important role in 2.3 Chronic tension-type headache. Increased pericranial tenderness recorded by manual palpation is the most significant abnormal finding in patients with tension-type headache. The tenderness is typically present interictally, is further increased during actual headache and increases with the intensity and frequency of headaches. Pericranial tenderness is easily recorded by manual palpation by small rotating movements and a firm pressure (preferably aided by use of a palpometer) with the second and third finger on the frontal, temporal, masseter, pterygoid, sternocleidomastoid, splenius and trapezius muscles. Local tenderness scores of 0-3 for each muscle can be summed to yield a total tenderness score for each individual. Palpation is a useful guide for treatment strategy. It also adds value and credibility to the explanations given to the patient.

Increased tenderness is most likely of pathophysiological importance. The Classification Committee encourages further research into the pathophysiological mechanisms and treatment of 2. Tension-type headache. With this aim, ICHD-II distingushed patients with and without such disorder of the pericranial muscles, and this subdivision is maintained in ICHD-3 (beta) to stimulate further research in this area.

The diagnostic difficulty most often encountered among the primary headache disorders is to discriminate between tension-type headache and mild migraine without aura. This is more so because patients with frequent headaches often suffer from both disorders. It has been suggested to tighten the diagnostic criteria for 2. Tension-type headache in the hope of excluding migraine that phenotypically resembles tension-type headache. Such an increase in specificity would, 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. Stricter diagnostic criteria for 2. Tension-type headache were proposed in the Appendix of ICHD-II, as A2. Tension-type headache, but so far with no evidence that such a change would be beneficial. These stricter diagnostic criteria remain in the Appendix, for research purposes only. The Classification Committee recommends comparisons between patients diagnosed according to each set of criteria, not only for characterization of clinical features but also for enquiry into pathophysiological mechanisms and response to treatments.