Left- vs right-sided migraine: a scoping review.

BACKGROUND: Migraine is a historically unilateral head pain condition, the cause of which is not currently known. A growing body of literature suggests individuals who experience migraine with left-sided headache ("left-sided migraine") may be distinguished from those who experience migraine with right-sided headache ("right-sided migraine"). OBJECTIVE: In this scoping review, we explore migraine unilaterality by summarizing what is currently known about left- and right-sided migraine. METHODS: Two senior medical librarians worked with the lead authors to construct and refine a set of search terms to identify studies of subjects with left- or right-sided migraine published between 1988, which is the year of publication of the first edition of the International Classification of Headache Disorders (ICHD), and December 8, 2021 (the date the searches were conducted). The following databases were searched: Medline, Embase, PsycINFO, PubMed, Cochrane Library, and Web of Science. Abstracts were loaded into Covidence review software, deduplicated, then screened by two authors to determine study eligibility. Eligible studies were those involving subjects diagnosed with migraine (according to ICHD criteria) in which the authors either: a) compared left- to right-sided migraine; or b) described (with analysis) a characteristic that differentiated the two. Data were extracted by the lead author, including ICHD version, the definition of unilateral migraine used by the authors, sample size, whether the findings were collected during or between attacks, and their key findings. The key findings were grouped into the following themes: handedness, symptoms, psychiatric assessments, cognitive testing, autonomic function, and imaging. RESULTS: After deduplication, the search yielded 5428 abstracts for screening. Of these, 179 met eligibility criteria and underwent full text review. 26 articles were included in the final analysis. All of the studies were observational. One study was performed during attack, nineteen between attacks, and six both during and between attacks. Left- and right-sided migraine were found to differ across multiple domains. In several cases, reciprocal findings were reported in left- and right-migraine. For example, both left- and right-sided migraine were associated with ipsilateral handedness, tinnitus, onset of first Parkinson's symptoms, changes in blood flow across the face, white matter hyperintensities on MRI, activation of the dorsal pons, hippocampal sclerosis, and thalamic NAA/Cho and NAA/Cr concentrations. In other cases, however, the findings were specific to one migraine laterality. For example, left-sided migraine was associated with worse quality of life, anxiety, bipolar disorder, PTSD, lower sympathetic activity, and higher parasympathetic activity. Whereas right-sided migraine was associated with poorer performance on multiple cognitive tests, a greater degree of anisocoria, changes in skin temperature, higher diastolic blood pressure, changes in blood flow through the middle cerebral and basilar arteries, and changes on EEG. CONCLUSION: Left- and right-sided migraine differed across a wide range of domains, raising the possibility that the pathophysiology of left- and right-migraine may not be identical.

Exacerbation of headache during dihydroergotamine for chronic migraine does not alter outcome.

OBJECTIVE: To evaluate whether headache exacerbation associated with IV dihydroergotamine (DHE) infusion predicts medium-term headache outcome in patients with chronic migraine. METHODS: This was a retrospective chart review study of the UCSF Headache Center's use of IV DHE for chronic migraine from 2008 to 2012. Medium-term headache outcome was assessed at 6-week follow-up. Univariate and multivariate logistic regression models were used to assess for predictors of outcome. RESULTS: Patients with chronic migraine (n = 274) were treated with a course of IV DHE. Of 214 with 6-week follow-up, 78% had medium-term headache benefit. In a univariate logistic regression model, headache exacerbation with DHE was associated with lower odds of a positive medium-term headache outcome (odds ratio [OR] 0.43, 95% confidence interval [CI] 0.20-0.91). However, in the multivariate logistic regression model, headache exacerbation was no longer an independent predictor of treatment outcome (OR 0.65, 95% CI 0.28-1.51). Factors that independently predicted outcome were nausea (OR 0.12, 95% CI 0.02-1.00, p = 0.05), age (OR 1.68 for each decade increase in age, 95% CI 1.24-2.28), and medication overuse (OR 0.42, 95% CI 0.18-0.97). CONCLUSIONS: After controlling for nausea and other factors, headache exacerbation with DHE infusions is not an independent predictor of poor headache outcome and clinicians should not interpret its presence as a reason to stop treatment. The focus of management should be on controlling nausea as it is the most important modifiable factor in achieving a good headache outcome with an inpatient course of IV DHE for chronic migraine.