Purpose: To determine the incidence of sixth nerve palsy in a population-based study, with particular emphasis on associated coexisting medical conditions and to use these data to develop a management algorithm. Design: Retrospective, population-based case series. Participants: All residents of Olmsted County, Minnesota, USA, diagnosed with sixth nerve palsy between January 1, 1978 and December 31, 1992. Methods: All cases were identified by using the Rochester Epidemiology Project medical records linkage system, which captures all patient-physician encounters in Olmsted County. The entire medical record of each patient was reviewed to confirm the diagnosis, document county residency, and to determine associated medical conditions. We used stringent predetermined criteria to define diabetes mellitus and hypertension as associations. Incidence rates were adjusted to the age and gender distribution of the 1990 white population in the United States. Main Outcome Measures: Etiology or systemic associations of the palsy. Results: We identified 137 new cases of sixth nerve palsy over the 15-year period. The age- and gender-adjusted annual incidence of sixth nerve palsy was 11.3/100 000 (95% confidence interval, 9.3-13.2/100 000). Causes and associations were: undetermined (26%), hypertension alone (19%), coexistent hypertension and diabetes (12%), trauma (12%), multiple sclerosis (7%), neoplasm (5%), diabetes alone (4%), cerebrovascular accident (4%), postneurosurgery (3%), aneurysm (2%), and other (8%). When sixth nerve palsy was the presenting sign in cases of neoplasm (n = 1) and aneurysm (n = 3), history and examination revealed the presence of other neurologic symptoms or signs. Conclusions: We provide population-based data on the incidence of sixth nerve palsy with a notably lower incidence of neoplasm and higher incidence of diabetes and hypertension than previous institution-based series. We suggest that patients with nontraumatic neurologically isolated sixth nerve palsy may undergo a focused medical evaluation followed by close observation, whereas non-neurologically isolated cases warrant a full neurologic evaluation, including prompt neuroimaging.
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