Prachi Mehndiratta, MD

Grewal K, Austin PC, Kapral MK, H, and Atzema CL. Missed Strokes Using Computed Tomography Imaging in Patients With Vertigo:Population-Based Cohort Study. Stroke. 2014

Is the vertigo of peripheral or central origin? This is always the dilemma in patients that present with the non-specific symptom of dizziness to the emergency room. About 3% of patients per year that present to the ER with dizziness and vertigo symptoms are diagnosed with stroke. History and examination are not foolproof in ascertaining the origin of vertigo and work up is often at the discretion of the physician in charge.

This Canadian study attempted to determine if there were differences in the number of short or long-term strokes in patients admitted to the ER with “peripheral vertigo” and underwent a non-contrast CT head for screening. The investigators utilized the Canadian Institutes of Health Information National Health Care Ambulatory Reporting System (CIHI-NACRS), which is an anonymized database of all ER visits in Ontario, Canada. Patients aged 18-105 years, with a ICD 10 diagnosis of peripheral vertigo, admitted to the ER between April 2006 and March 2011 were included.  Patients admitted to urgent care centers; those who died in the ER or were admitted to the hospital from the ER and those with recurrent ER visits were excluded. It was assumed that those who were discharged from the ER had a negative CT scan of the head.

Propensity-score matching a.k.a. the likelihood of receiving a CT head based on comorbidities was performed for the two groups of patients- those who underwent a CT head and those who did not. Multivariate logistic regression was used to estimate this propensity score. Outcomes of strokes within 30 day, 90 days and 365 days as well all cause mortality were calculated between the two groups.

A total of 8,596 (20.6%) received head CT imaging in the ED out of 41,794 total patients. The majority were without contrast (96.9%). Median age in both groups was 63.0 years (IQR 51.0-74.0) and 62% were female. Risk factor distribution was similar in the two groups and amongst the exposed patients these strokes occurred markedly earlier after ED discharge (median 32 days, IQR 4.0-133.0) than among unexposed patients (median 105 days, IQR 11.5-204.5). The relative risk of stroke at 30 days among exposed patients was twice (2.27; 95% CI, 1.12-4.62) that of unexposed patients.

The authors justify the higher rate of strokes in the group receiving CT imaging by the increased risk for a stroke in the peri-TIA period. It is also conceivable that these patients had cerebellar or brainstem stroke that was poorly visualized on a non contrast CT. These results must be understood in light of its limitations. This is a retrospective cohort, albeit with a large number of patients. Both groups were similar in terms of risk factors but not much is known about their clinical presentation, difference in exam and the reason for CT examination. Additionally any study utilizing ICD 10 codes is subject to inaccuracies in coding. The finding of increased number of strokes in the short term after an ER admission and CT scanning for vertigo highlights that these patients should instead be imaged by means of a MRI scan that is more sensitive for stroke in the posterior fossa.