Transient global amnesia. The rare, sudden development of dense anterograde amnesia occurs without alteration in level of consciousness, focal neurologic deficits, or seizure activity. It is self-limiting and mainly affects those older than 50. Transient global amnesia has an uncertain etiology, although atypical migraine, seizure discharge, and venous congestion with hippocampal ischemia are viewed as possible causes. Reported triggers include severe physical or emotional stress, strenuous physical activity, and orgasmic sexual intercourse.21
TABLE 2
Common stroke mimics9,11,12,14,22
Condition | Misdiagnosed as stroke (%) |
---|---|
Brain tumor | 7-15 |
Labyrinthitis | 5-6 |
Metabolic disorder | 3-13 |
Migraine | 11-47 |
Psychiatric disorder | 1-40 |
Seizures | 11-40 |
Sepsis | 14-17 |
Syncope | 5-22 |
Transient global amnesia | 3-10 |
Other | 11-37 |
In the ED: Evaluation is guided by a timeline
Current guidelines from the American Heart Association and American Stroke Association recommend that a possible stroke patient be evaluated by the physician in the ED within 10 minutes of his or her arrival—and that a decision on how to proceed be reached within 60 minutes of arrival. The guidelines call for the initial computed tomography (CT) to be completed within 25 minutes of the patient’s arrival and interpreted by a physician with expertise in reading CT studies within 45 minutes of arrival.6,24
In the ED, the National Institutes of Health Stroke Scale (NIHSS)25 (TABLE 3) is an ideal way to focus and record the neurological exam.6 The scale assesses 6 separate neurologic functions (level of consciousness, vision, motor function, sensory function, language, and cerebellar function) and can be performed within 5 to 8 minutes. It yields a score from 0 to 42, with the higher numbers indicating worse neurologic function.26 Although a score ≤10 is generally considered to be predictive of a stroke mimic, a recent study found that 19% of patients with an NIHSS score >10 also had conditions masquerading as stroke.27
Imaging leads to accurate diagnosis. The rate at which stroke mimics are mistaken for actual strokes varies with the population studied and the diagnostic tests performed. While stroke is largely a clinical diagnosis and a history and physical exam focused on onset, duration, and symptoms are key elements in differentiating stroke from a stroke mimic, studies have found that the incidence of misdiagnosis (19% with history, physical, and lab work alone) drops to 5% when noncontrast CT is added. When diffusion-weighted magnetic resonance imaging (MRI) is used instead, misdiagnosis drops to just 2%.11,12,14,22,23
Basic lab tests—a complete blood count and basic metabolic panel, with blood alcohol, hepatic function tests, and toxicology screens in select cases—help rule out stroke mimics. Radiographic imaging of the brain provides further clarification (FIGURE 1A AND 1B), serving 2 main purposes: to (1) evaluate diagnoses other than stroke and (2) identify the presence of any acute intracranial bleeding. Noncontrast CT scans detect acute hemorrhage with a sensitivity of 89% and specificity of 100%.27 CT angiography (which can identify the location of a clot) and CT perfusion (which allows an assessment of any existing penumbra) can also be obtained in a timely fashion with newer multislice scanners.
Some institutions, however, evaluate acute stroke patients with MRI. Depending on the sequences used, MRI has the advantage of being able to detect early ischemic changes, diffusion and perfusion mismatches, and abnormalities of the posterior fossa.29 In acute ischemic stroke, diffusion-weighted MRI has a sensitivity of 83% and specificity of 96%, compared with a sensitivity of 16% and specificity of 98% for noncontrast CT.28
TABLE 3
National Institutes of Health Stroke Scale25
Item | Response score* |
---|---|
1a. Level of consciousness | 0 = alert 1 = not alert 2 = obtunded 3 = unresponsive |
1b. Level of consciousness Questions | 0 = answers both correctly 1 = answers one correctly 2 = answers neither correctly |
1c. Level of consciousness Commands | 0 = performs both tasks correctly 1 = performs one task correctly 2 = performs neither task correctly |
2. Gaze | 0 = normal 1 = partial gaze palsy 2 = total gaze palsy |
3. Visual fields | 0 = no visual loss 1 = partial hemianopsia 2 = complete hemianopsia 3 = bilateral hemianopsia |
4. Facial palsy | 0 = normal 1 = minor paralysis 2 = partial paralysis 3 = complete paralysis |
5. Motor arm a. Left b. Right | 0 = no drift 1 = drifts before 5 sec 2 = falls before 10 sec 3 = no effort against gravity 4 = no movement |
6. Motor leg a. Left b. Right | 0 = no drift 1 = drifts before 5 sec 2 = falls before 10 sec 3 = no effort against gravity 4 = no movement |
7. Ataxia | 0 = absent 1 = 1 limb 2 = 2 limbs |
8. Sensory | 0 = normal 1 = mild loss 2 = severe loss |
9. Language | 0 = normal 1 = mild aphasia 2 = severe aphasia 3 = mute or global aphasia |
10. Dysarthria | 0 = normal 1 = mild 2 = severe |
11. Extinction/inattention | 0 = normal 1 = mild 2 = severe |
* Yields a score from 0 to 42 (higher numbers indicate worse neurologic function). |