Have you ever experienced a headache of any kind?

To the editor:

I read with interest the article by Olofsson et al., reporting an estimate of lifetime headache freedom among a large cohort of healthy blood donors (1). The authors hypothesize that this group may provide insight into novel protective factors. Approximately 4% self-reported a negative response to the question: “Have you ever experienced a headache of any kind?” Male sex, more regular alcohol consumption, employment status as a student and being in the lowest income quintile were associated with not reporting a headache. Conversely, being in the highest quintile of educational attainment was negatively associated with headache freedom.

In addition to the interesting hypotheses discussed in the manuscript, there are additional considerations. In the ICHD-3, headache is defined as “pain (qv) located in the head, above the orbitomeatal line and/or nuchal ridge.” However, not everyone with a headache will describe their symptoms in term of pain. Anecdotally, I recently encountered a gentleman who insisted that his moderately severe head “pressure” not be labeled as a “headache.” This was not the first time. This has been termed a word-selection bias and likely accounts in part for some non-reporting of headache, highlighting a key limitation in any diagnosis dependent on patient self-report.

The impact of gender on pain detection threshold, appraisal and reporting has been challenging to disentangle (2). However, men and women appear to differ more in their tendencies to label an experimental stimulus as painful or not, than in their detection of changes in stimulus intensities (2). The recently developed Sensation and Pain Rating Scale attempts to better capture a zone of uncertainty, rather than a distinct cut-off point, when an individual decides a non-painful sensation becomes painful (3). Future research might address whether the width of this zone is impacted by gender.

Cognitive beliefs may also contribute to a reluctance to label sensations as pain, including stigma, stoicism, cautiousness, fatalism (pain is inevitable), bother (mentioning pain would just be complaining), and denial (4). The Danish Blood Donor Study does include record of identifying information for participant contact, and therefore the contribution of these elements cannot be excluded.

In future work, these biases could be addressed by follow-up interview of those positively screening for headache freedom. The screening question used in the study could be validated among a representative cohort with episodic tension-type headache to better understand the test sensitivity (e.g. false negative rate). Finally, validated screening tools exist to identify cognitive beliefs about pain (4).