Migraine a risk factor for SSNHL

Abstract

Among patterns of hearing loss, sudden sensorineural hearing loss (SSNHL) ranks as one of the least common, accounting for 1% of all cases of hearing loss with approximately 4000 new cases reported each year (1). However, the inability to prepare for the sudden loss of function, the lack of a satisfying explanation for its cause, and the limited treatment options also make it a particularly devastating disorder. A specific cause for the hearing loss is found in less than 15% of cases and guidelines for management of SSNHL have only recently been published (2,3). Prior association studies have shown that traditional vascular risk factors such as smoking, hypertension, dyslipidemia, and diabetes can be risk factors for SSNHL, with one study even showing a higher risk of subsequent stroke in patients with SSNHL (4). However, meta-analyses have shown that these associations are also inconsistent (5). Although a history of migraine is not generally considered to be a risk factor for SSNHL, it has also not been systematically investigated. Case reports have indicated that some patients who experience SSNHL also experience other symptoms attributable to migraine and that sudden hearing loss associated with a severe migraine headache can be associated with ischemic changes in the inner ear (6,7). In this volume, Chu et al. report on the association between migraine and the incidence of SSNHL over a 10-year period using the National Health Insurance Research Database in Taiwan, which is based on a universal health care system with centralized information on all diagnostic codes and prescriptions. The study was designed as a retrospective case-control study, with the incidence of SSNHL in migraine patients and controls in the year 2000 used as the baseline. Migraine and SSNHL were both diagnosed by ICD9-CM codes, as were major vascular risk factors such as diabetes, hypertension, dyslipidemia, and atrial fibrillation. After exclusion of a history of SSNHL at baseline, Meniere’s disease, and acoustic neuromas, 10,280 migraine patients were compared to 41,120 controls. These subjects were followed for a median of five years until one of three outcomes was obtained: 1) development of SSNHL, 2) subject death, or 3) end of the study in 2009. The study required that the diagnosis of migraine be coded by a neurologist and that the diagnosis of SSNHL be coded by an otolaryngologist. The authors report a 1.8-fold increased risk of SSNHL in patients with migraine with a very small but detectable cumulative risk of SSNHL each year throughout the 10 years of observation. This cumulative risk amounted to 0.4% in migraine patients and 0.2% in controls. In a multivariate analysis, comorbidity with hypertension increased the risk to 1.92 in migraine patients, but this was not statistically significant. The role of hypertension in the risk of SSNHL in controls was not reported, however. The study provides a global perspective on the incidence of SSNHL. The authors calculated an incidence of 81.6 cases in 100,000 person-years in migraine subjects and 45.7 cases per 100,000 person-years in controls. The relative risk increased to 118.6 per 100,000 person-years in migraine subjects over the age of 40 years. These estimates are much higher than the often-reported incidence of five to 20 cases in 100,000 person-years for SSNHL (2,3,5). However, some widely cited incidence data in the current literature are extrapolated from as few as 18 patients cared for in one health care system or are reported frompersonal communications (8,9). Older studies also did not use the current, more generally accepted criteria for SSNHL that require a loss of 30 dBof hearing in three consecutive frequencies occurring over less than 72 hours. Conversely, the reported incidence in the study was lower than the 160 per 100,000 person-years reported in 2004 from a German population (10). One challenge to making an accurate assessment of the incidence of SSNHL in any setting is that acuity can often be difficult to determine, especially if the patient recovers quickly. Between one-third and two-thirds of