Intended for healthcare professionals

Rapid response to:

Primary Care 10-minute consultation

Headache

BMJ 2005; 330 doi: https://doi.org/10.1136/bmj.330.7487.346 (Published 10 February 2005) Cite this as: BMJ 2005;330:346

Rapid Response:

Re: Causes of headache

The cause or causes of migraine and of other primary headaches remain unidentified. For all we know, therefore, any given thing might cause primary headaches. Indeed, primary headaches have been blamed on a variety of things, including diet, weather, stress, hormones, computer screens, odors, posture and lack of sleep, to name a few.

A systematic approach to sorting through suspected primary headache causes is called for. There's an important difference between posture and caffeine: posture has never been demonstrated to cause headache. Caffeine has been.

On the one hand, nearly the entire general population regularly uses a drug, caffeine, demonstrated to cause severe episodic headache and nausea/ vomiting. On the other hand, mysterious headache is pandemic. Perhaps there is a connection between those two facts.

Criterion E of the International Headache Society (IHS) diagnostic criteria for migraine requires the physician rule out conditions including caffeine- caused headache before making a diagnosis of migraine. By definition, therefore, caffeine-caused headache cannot be migraine. The IHS diagnostic criteria separate by decree two conditions never separated in fact.

No physician has ever ruled out caffeine-caused headache before diagnosing migraine. The only known way to rule out caffeine-caused headache is to rule out caffeine use, something which has never been done in a migraine patient. Besides: physicians routinely diagnose migraine in patients who report using caffeine.

Because caffeine-caused headache can fulfill the diagnostic criteria for migraine (except for criterion E, of course), caffeine-caused headache must sometimes be diagnosed as migraine. How often this happens, nobody knows. Nor is it known whether caffeine-caused headache that resembles migraine is never, sometimes or always genuine migraine.

Studies of migraine have consistently failed to control for caffeine- caused headache, which means caffeine-caused headaches that occur during those trials may be counted as migraines. Researchers have been observing not migraine but an amalgam of migraine and caffeine-caused headache.

Competing interests: None declared

Competing interests: No competing interests

21 March 2005
Barry A Spencer
unemployed
San Francisco, California U.S.A. 94110