1.5 Probable migraine

Previously used term:
Migrainous disorder.

Coded elsewhere:
Migraine-like headache secondary to another disorder (symptomatic migraine) is coded according to that disorder.

Description:
Migraine-like attacks missing one of the features required to fulfil all criteria for a subtype of migraine coded above, and not fulfilling criteria for another headache disorder.

Diagnostic criteria:
A. Attacks fulfilling all but one of criteria A-D for 1.1 Migraine without aura, or all but one of criteria A-C for 1.2 Migraine with aura
B. Not fulfilling ICHD-3 criteria for any other headache disorder
C. Not better accounted for by another ICHD-3 diagnosis.

Comment:
In making a headache diagnosis, attacks that fulfil criteria for both 2. Tension type headache and 1.5 Probable migraine are coded as the former in accordance with the general rule that a definite diagnosis always trumps a probable diagnosis. However, in patients who already have a migraine diagnosis, and where the issue is to count the number of attacks they are having (for example, as an outcome measure in a drug trial), attacks fulfilling criteria for 1.5 Probable migraine should be counted as migraine. The reason for this is that mild migraine attacks, or attacks treated early, often do not achieve all characteristics necessary for a migraine attack diagnosis but nevertheless respond to specific migraine treatments.