Migraine Linked to Risk for Bell's Palsy
Medscape Medical News
December 18, 2014

Patients with migraine have almost double the risk of developing Bell's palsy compared with those without migraine, researchers report.

Their observational cohort study of patients with migraine and matched controls found that the association between migraine and Bell's palsy, an acute, ipsilateral facial nerve paralysis that results in weakness of the platysma and muscles of facial expression, was not affected by sex or migraine subtype.

The results suggest that physicians should ask patients about migraine, study author Shuu-Jiun Wang, MD, deputy director, Neurological Institute, Taipei Veterans General Hospital, and chairman, Faculty of Medicine, National Yang-Ming University School of Medicine, Taipei, Taiwan, told Medscape Medical News.

"In clinical practice, in addition to hypertension, diabetes, and pregnancy, migraine history should be traced in patients with Bell's palsy," said Dr Wang. He stressed that this is especially important in young people, who usually don't have hypertension or diabetes.

Their findings were published online December 17 in Neurology.

Researchers used data from the Taiwan National Health Insurance Research Database (NHIRD) to assemble two cohorts aged 18 years and older: (1) all patients diagnosed with migraine (migraine with aura, migraine without aura, and migraine unspecified) from January 2005 to December 2009 and (2) matched controls without migraine or other headache extracted from a random sample in NHIRD.

Participants with Bell's palsy at baseline were excluded from the study, as were those in whom migraine and Bell's palsy were both diagnosed within 30 days.

To minimize baseline differences between the patients with migraine and participants without migraines, researchers used propensity score matching. For each patient in the migraine cohort, they identified one control participant with similar demographic characteristics, matched in terms of age and propensity score for the likelihood of a migraine diagnosis.

The propensity score–matched analysis included 136,704 participants in each of the migraine and control cohorts.

After a mean follow-up of 3.2 years, 671 persons in the migraine group and 365 in the control group were newly diagnosed with Bell's palsy. The incident rates were 158.1 and 83.2 per 100,000 patient-years, respectively.

This incidence of Bell's palsy in the control group was higher than previously reported (13.1 to 53.3 per 100,000 person-years). This discrepancy, said Dr Wang, might be explained by the accessibility and global coverage of Taiwan's National Health Insurance plan.

Migraine is quite common, with an annual global prevalence of about 10%. It affects more females than males. The male-to-female ratios of Bell's palsy in this study were 1.4 to 1 in the migraine cohort and 1.1 to 1 in the control cohort.

Patients with migraine had greater risk for Bell's palsy (hazard ratio, 1.91; 95% confidence interval, 1.68 - 2.17; P < .001). The association between migraine and Bell's palsy was similar with and without propensity score matching.

The association remained significant with use of different diagnostic criteria for Bell's palsy, and it was consistent in subgroups defined according to sex, age, Charlson Comorbidity Index score, diabetes, hypertension, and migraine subtype.

"We did not find a difference between migraine with aura and without aura," commented Dr Wang. "This is in contrast to prior studies on vascular comorbidities," which showed that migraine with aura but not migraine without aura is associated with stroke or myocardial infarction.

Migraineurs with more clinic visits for migraine were more likely to develop Bell's palsy, said Dr Wang. "We hypothesize that more frequent or severe migraine attacks might predispose facial nerves to subsequent Bell's palsy."

Dr Wang said he was somewhat surprised by the study results, although he and his colleagues had already reported that patients with migraine have a higher chance of developing sudden sensorineural hearing loss related to the eighth cranial nerve, or the cochlear nerve. "So we thought that we might have a chance to demonstrate the association between migraine and Bell palsy."

Hypothesis
Several mechanisms may explain the link between migraine and Bell's palsy, but the "top hypothesis," according to Dr Wang, is that neurogenic inflammation of nearby cranial nerves may predispose the facial nerve to demyelination, perhaps after a viral infection. Dr Wang noted that the study excluded patients with concomitant herpes zoster infection within 30 days but that researchers had no access to patient laboratory data.

"It's premature to either rule in or rule out the role of neurogenic infection," he said.

A shared mechanism between migraine and Bell's palsy might be at play. "However, most studies show migraine with aura, but not migraine without aura, is linked to vascular comorbidities," noted Dr Wang. The lack of differential effects between migraine with and without aura in the current study "renders this hypothesis behind neurogenic inflammation" in terms of plausibility, he said.

A limitation of the study was that Bell's palsy is primarily a clinical diagnosis and the database has limited clinical information, so some cases may have been due to another cause of facial weakness. As well, the migraine cohort had active migraine, possibly leading to the under-representation of people with nonactive migraine.

The study results have several implications, Stephen Silberstein, MD, Thomas Jefferson University, Philadelphia, Pennsylvania, and Mauro Silvestrini, MD, Marche Polytechnic University, Ancona, Italy, write in an accompanying editorial.

"Besides suggesting a role for migraine as a risk factor for Bell palsy, the authors raise a number of hypotheses about the presence of common mechanisms underlying both diseases," they write.

"The possibility that inflammation, infection, and vascular changes may be implicated in sustaining the association between migraine and Bell palsy is worthy of further investigation to obtain insight about new therapeutic strategies."

The study was supported by the National Science Council of Taiwan, the Taipei Veterans General Hospital, National Yang-Ming University, and the Taiwan Ministry of Education. Dr Wang has served on the advisory boards of Allergen and Eli Lilly Taiwan. He has received speaking honoraria from local companies (Taiwan branches) of Pfizer, Eli Lilly, and GSK. He has received research grants from the Taiwan National Science Council, Taipei Veterans General Hospital and Taiwan Headache Society. Dr Silberstein serves as a consultant and/or advisory board member and receives honoraria from Alder Biopharmaceuticals, Allergan Inc, Amgen, Avanir Pharmaceuticals Inc, eNeura Inc, ElectroCore Medical LLC, Medscape LLC, Medtronic Inc, Mitsubishi Tanabe Pharma America Inc, National Institutes of Neurological Disorders and Stroke, Pfizer Inc, Supernus Pharmaceuticals Inc, and Teva Pharmaceuticals. Dr Silvestrini has disclosed no relevant financial relationships.

Neurology. Published online December 17, 2014. Abstract Editorial