Could a stroke causing dizziness be missed? Part II
Retrospective studies of misdiagnosis of Cerebellar Stroke (CS) reveal that the most common medical errors include failure to perform appropriate screening exams, choosing a diagnosis that does not explain all the presenting symptoms, failure to consider CS as a differential diagnosis based on the patient’s age, and the ordering of the inappropriate neuro-imaging study . When the risk factors, symptoms and clinical signs suggest the possibility of cerebellar or brainstem infarction, specific neuro-imaging (CT or MRI scanning) can help verify this suspicion, but are pretty poor at ruling them out.
Imaging
Patients presenting with dizziness and vertigo are often referred for Computerized Tomographic (CT) scan of the brain. CT scans are frequently normal in the first few hours following acute ischemic stroke, therefore, a normal CT scan cannot rule out CS. As many as 50% to 74% of CS patients may be missed if the diagnosis is dependent on CT scanning (Simmons, Biller, Adams, Dunn, & Jacoby, 1986; Chalela et al., 2007). CT studies are particularly poor for ruling out brainstem stroke as that area is often poorly visualized due to surrounding bone structures. The American College of Radiology recommends “MRI of the head without and with contrast” as the appropriate test for the complaint of vertigo with no hearing loss (ACR, 1996). Although MRI has significantly higher sensitivity than CT, the examiner must not rely totally on MRI findings to identify or rule out cerebellar stroke. Twelve percent of CS patients had normal MRI exams on initial presentation, with abnormal exams a few days later (Kattah et al. 2009). Similarly, Chalela et al. (2007) report that 17% of patients diagnosed with acute stroke had normal MRI exams on initial presentation, commenting that there is a higher likelihood of a false-negative MRI exam when the stroke is located in the brainstem. So the old adage, “Let’s get an MRI just to be sure,” isn’t such a sure bet after all.
Next week –Is there a better way?
References:
American College of Radiology. (1996). ACR Appropriateness Criteria. Last review date: 2006.
Chalela JA, Kidwell CS, Nentwich LM, Luby M, Butman JA, Demchuk AM, Hill MD, Patronas N, Latour L, Warach S. (2007) Magnetic resonance imaging and computed tomography in emergency assessment of patients with suspected acute stroke: a prospective comparison. Lancet., Jan 27;36
Kattah, J., Talkad, A., Wang, D., Hsieh, Y., & Newman-Toker, D. (2009). HINTS to diagnose stroke in the acute vestibular syndrome: three-step bedside oculomotor examination more sensitive than early MRI diffusion-weighted imaging. Stroke, 3504-3510.
Simmons, Z., Biller, J., Adams, H. Jr, Dunn, V., & Jacoby, C. (1986). Cerebellar infarction: comparison of computed tomography and magnetic resonance imaging. Ann Neurol, 19, 291-293.
