Headache Triggers as Surprise

To examine the hypothesis that surprising experiences of headache triggers are associated with daily headache activity.

Little is known about the specific environmental or behavioral interactions that might trigger a headache attack in a prone individual. We propose that headache trigger exposures can be usefully characterized, not only by their mechanisms of action, but also on the degree of "surprise" they present to the individual. This hypothesis is based on elements of information theory: that unusual events and experiences carry more information than common events and experiences and that headache attacks are associated with reactions to uncommon or unexpected biopsychosocial exposures.

A secondary analysis of the Headache Prediction Study, this prospective cohort study followed N = 95 individuals with episodic migraine who contributed 4195 days of diary data. Information was collected on daily levels of several common headache triggers: number of caffeinated beverages, number of alcoholic beverages, stress (Daily Stress Inventory), and mood disturbance (Profile of Mood States). The probability of observing variations in each trigger was used to estimate the "surprisal" of experiencing each trigger, and this information, measured in bits, was used to predict headache attacks.

Participants experienced a headache attack on 1613 of 4195 days (38.5%). Each of the triggers was modestly related to the probability of experiencing a future headache in a complex manner that involved interactions between current headache status, current levels of the trigger, and lagged (previous) levels of the trigger. However, when expressed as a surprisal, the associations were simplified and strengthened. For example, each of the individual trigger surprisals exhibited a meaningful association with the development of a future headache attack (expressed as a 1 SD change in surprisal), with odds ratios ranging from a low of 1.11 (95%CI: 1.00 to 1.24) for alcohol to a high of 1.30 (95%CI: 1.14 to 1.46) for stress. The individual surprisals could be summed for total trigger surprise and exhibited a reliable association with new onset headache, OR 1.35 (95%CI: 1.17 to 1.49). This score exhibited superior discrimination between headache and non-headache days from all of the individual triggers (ignoring base rate, AUC: 0.61; AUC: 0.71 with base rate).

Diverse headache triggers can be uniformly described using their probability distributions. Rare values of headache triggers, or surprising values, were found to have consistent associations with headache activity across a variety of triggers. This finding, if validated in external data using other triggers, has potential to be used to conceptualize the influence of a wide range of headache triggers.