|2||TENSION-TYPE HEADACHE (TTH)||G44.2|
|Previously used terms||Tension headache, muscle contraction headache, psychomyogenic headache, stress headache, ordinary headache, essential headache, idiopathic headache and psychogenic headache|
|Coded elsewhere||Tension-type-like headache attributed to another disorder is coded to that disorder.|
Primary or secondary headache or both?
When a headache with tension-type characteristics occurs for the first time in close temporal relation to another disorder that is a known cause of headache, it is coded according to the causative disorder as a secondary headache. When pre-existing tension-type headache is made worse in close temporal relation to another disorder that is a known cause of headache, there are two possibilities, and judgment is required. The patient can either be given only the tension-type headache diagnosis or be given both the tension-type headache diagnosis and a secondary headache diagnosis according to the other disorder. Factors that support adding the latter diagnosis are: a very close temporal relation to the disorder, a marked worsening of the tension-type headache, very good evidence that the disorder can cause or aggravate tension-type headache and, finally, improvement or resolution of tension-type headache after relief from the disorder.
This is the most common type of primary headache: its lifetime prevalence in the general population ranges in different studies from 30 to 78%. At the same time, it is the least studied of the primary headache disorders, despite the fact that it has the highest socio-economic impact.
Whilst this type of headache was previously considered to be primarily psychogenic, a number of studies have appeared after the first edition of The International Classification of Headache Disorders that strongly suggest a neurobiological basis, at least for the more severe subtypes of tension-type headache.
The division into episodic and chronic subtypes that was introduced in the first edition of the classification has proved extremely useful. The chronic subtype is a serious disease causing greatly decreased quality of life and high disability. In the present edition we have decided to subdivide episodic tension-type headache further, into an infrequent subtype with headache episodes less than once per month and a frequent subtype. The infrequent subtype has very little impact on the individual and does not deserve much attention from the medical profession. However, frequent sufferers can encounter considerable disability that sometimes warrants expensive drugs and prophylactic medication. The chronic subtype is of course always associated with disability and high personal and socio-economic costs.
The first edition arbitrarily separated patients with and without disorder of the pericranial muscles. This has proved to be a valid subdivision but the only really useful distinguishing feature is tenderness on manual palpation and not, as suggested in the first edition, evidence from surface EMG or pressure algometry. Therefore, we now use only manual palpation, preferably as pressure-controlled palpation, to subdivide all three subtypes of tension-type headache.
The exact mechanisms of 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. The classification subcommittee encourages further research into the pathophysiological mechanisms and treatment of tension-type headache.
There are some reasons to believe that, with the diagnostic criteria set out in the first edition, patients coded for episodic tension-type headache included some who had a mild form of migraine without aura and patients coded for chronic tension-type headache included some who had chronic migraine. Clinical experience favours this suspicion, especially in patients who also have migraine attacks, and some patients may display pathophysiological features typical of migraine (Schoenen et al, 1987). Within the classification subcommittee there was an attempt to tighten the diagnostic criteria for tension-type headache for the second edition, with the hope to exclude migraine patients whose headache phenotypically resembles tension-type headache. However, this would have compromised the sensitivity of the criteria and there was no evidence to show the beneficial effects of such a change. Therefore a consensus was not reached, but a proposal for new, stricter diagnostic criteria is published under A2 Tension-type headache in the appendix. The classification subcommittee recommends comparisons between patients diagnosed according to the explicit criteria and others diagnosed according to the appendix criteria. This pertains not only to the clinical features but also to pathophysiological mechanisms and response to treatments.