Ask someone how often they get migraine attacks and you will usually get a range: “a few times a month, more when work is bad.” Ask them to count the last ninety days and the number is almost always different — sometimes lower, often higher. Neither answer is dishonest. Pain is a bad thing to remember accurately, and the months that were worst are the ones that crowd out the rest.
This matters because the number is not trivia. It is the input to a decision.
The three numbers
A headache diary exists to produce three figures, and almost everything else in it is in service of those three.
1. Headache days per month
Not attacks — days. An attack that runs from Tuesday evening into Thursday morning is three headache days, and counting it as one is the single most common way a diary understates what is happening.
The count matters because the thresholds in the diagnostic criteria are written in days. The ICHD-3 defines chronic migraine as headache on 15 or more days per month for more than three months, with at least eight of those days having the features of migraine. Below that line the same person may meet the criteria for episodic migraine. The line is not a value judgement and it is not about how much it hurts — it is a frequency boundary, and you cannot sit on either side of it without a count.
2. Duration
How long an attack runs when it is not treated, and how long it runs when it is. Those two figures together are the closest thing a diary gives you to a measure of whether something is working. A treatment that turns a two-day attack into a six-hour one has done something, even if the pain at its peak felt the same.
3. Treatment days
The number of days in a month you take something for a headache — any acute medication, prescription or not. This is the figure people are most surprised by, and it has its own article, because taking acute medication on too many days a month can, over time, make headaches worse rather than better. The ICHD-3 sets the thresholds for that, and they are lower than most people expect.
What a useful entry looks like
Short, in the moment, and the same every time.
Short, because the moment you most need to record something is the moment you are least able to. A twenty-minute form is a form that gets filled in on the good days and skipped on the bad ones, which biases the record in exactly the wrong direction.
In the moment, or as near to it as you can manage. Retrospective reconstruction at the end of the week is not a diary; it is the same guess you would have made without one.
The same every time, because a change in what you record looks identical to a change in what is happening. If you start logging the mild days in March, your April looks worse than your February for reasons that have nothing to do with your head.
Four ways a diary stops being useful
- Only the bad ones get logged. The mild days are the ones that move you across a frequency threshold, and they are the ones nobody bothers to record.
- The fields keep changing. Adding a new thing to track is fine; quietly dropping an old one breaks the comparison with every previous month.
- Interpretation gets recorded instead of observation. “Stress headache” is a conclusion. “Right side, 6/10, woke with it, slept five hours” is an observation, and only one of the two is still useful in six months when you have changed your mind about the cause.
- It never gets looked at. A diary that is only ever written into is a chore. The point is the shape it makes over eight or twelve weeks.
What a diary does not do
It does not diagnose anything. Frequency and duration are consistent with many things, and separating migraine from the other headache disorders is a clinical judgement made by a person who can also examine you and take a history. A diary is evidence brought to that conversation, not a replacement for it.
It also does not prove what caused an attack. That is a harder problem than it looks, and it has its own article too.
What it does is turn “a few times a month, more when work is bad” into something a clinician can act on in the fifteen minutes you have with them.
Sources
- Headache Classification Committee of the International Headache Society. The International Classification of Headache Disorders, 3rd edition (ICHD-3). Cephalalgia 2018;38(1):1–211. ichd-3.org
Written in house and checked against the ICHD-3. Where this page describes the state of the evidence rather than a specific finding, it says so, and it cites nothing it cannot point at. A named clinical reviewer is to be appointed before launch. Found an error? Tell us and we will correct it on the page.
