Table 2 -2 General rules for headache classification

• If the patient has more than one headache disorder, all should be diagnosed in the order of importance indicated by the patient.
• To make a diagnosis, all letter headings of a set of diagnostic criteria must be fulfilled.
• After each diagnosis, add estimated number of headache days per year in brackets.

• Diagnostic criteria given at the one- or two-digit level must generally be met by the subforms, but exceptions and/or more specific criteria are listed under the subforms.
• Patients who develop a particular form of headache for the first time in close temporal relation to the onset of one of the disorders listed in groups 5-11 are coded to these groups using the fourth digit to specify the type of headache. A causal relationship is not necessarily indicated however. Preexisting migraine, tension-type headache, or cluster headache aggravated in close temporal relation to one of the disorders listed in groups 5-11 are still coded as migraine, tension-type headache, or cluster headache (groups 1-3). If the number of headache days increases by 100% or more, the aggravating factor may be mentioned in parentheses, but it is not coded.
• Code to the degree (number of digits) that suits your purpose.
• If one headache type fits the diagnostic criteria for different categories of headache, code to the first headache category in the classification for which the criteria are fulfilled (1.7, 2.3, and 3.3 are not regarded as diagnoses if the headache also fulfills another diagnosis).
• If a patient has a form of headache that fulfills one set of diagnostic criteria, similar episodes that do not quite satisfy the criteria also usually occur. This can be due to treatment, lack of ability to remember symptoms exactly, and other factors. Ask the patient to describe a typical untreated attack or an unsuccessfully treated attack, and ascertain that there have been enough of these attacks to establish the diagnosis. Then, estimate the days per year with this type of headache, adding treated attacks and less typical attacks.
• A major obstacle to an exact diagnosis is reliance on the patient’s history to determine whether criteria are met. In less clear cases, have the patient record the attack characteristics prospectively, using a headache diary, before the diagnosis is made.
• If a fourth digit is to be used in association with a diagnosis at the two-digit level, insert 0 as the third digit.

Source: Headache Classification Committee of the International Headache Society (1988).

Editors: Silberstein, Stephen D.; Lipton, Richard B.; Dalessio, Donald J.