________________________________________________________________________ Dizziness and Vertigo
TESTING TO DIFFERENTIATE POSTERIOR CIRCULATION STROKE FROM BENIGN PERIPHERAL VESTIBULAR DISORDER HINTS is performed in sequence. Test nystagmus first; HINTS is validated only in patients with nystagmus, and gaze testing is non-intrusive (i.e., head movement unnecessary). • Gaze testing: Is there a central pattern of nystagmus? Patients with s-AVS and worrisome nystagmus, skew deviation, or bilateral normal HIT have a presumed stroke and should be admitted to a hospital. If all three tests seem reassuring, perform a targeted neurologic exam to determine if there are any CNS signs. This involves testing for: • 4D symptoms: – Diplopia (double vision) • Alternate cover test: Is skew deviation present? • HIT: Is the head impulse test result negative?
– Dysphagia (difficulty swallowing) – Dysarthria (difficulty with speech) – Dysmetria (lack of coordination)
• The cranial nerves for hearing • Anisocoria (unequal pupil size) • Facial loss of pain or temperature sensation • Cerebellar function for limb ataxia. The next step is gait testing to determine if the patient can walk unassisted.
If the answer to any of these questions is yes, the cause is presumed central and treated as stroke. If the answer to all questions is no, the cause is presumed peripheral. All answers must be no in order to exclude stroke because none is sufficiently sensitive individually. Source: [8; 10; 18] Table 1
An estimated 45,000 to 75,000 patients with stroke are misdi- agnosed annually. Roughly 28% to 59% of cerebellar strokes are misdiagnosed in the ED, and isolated dizziness is a risk factor for this misdiagnosis. Posterior circulation strokes are missed more than twice as often as anterior circulation strokes, and cerebellar strokes are four times more likely to be misdiag- nosed than stroke misdiagnosis overall. These misdiagnosed patients suffer higher mortality and disability at follow-up [10; 109; 110; 111]. CT is widely used but ineffective to rule out ischemic stroke in s-AVS; MRI with diffusion-weighted imaging (MRI-DWI) is markedly superior. However, within the first 48 hours of symptom onset, MRI-DWI is falsely negative in 12% to 18% of patients with AVS and 53% of patients with small brain- stem strokes. Posterior circulation strokes are five times more likely to be falsely negative than anterior circulation strokes. Indiscriminate CT angiography also has very low utility (1.3%) [8; 51; 112]. In the first 48 hours, physical examination outperforms MRI. If the initial physical examination suggests stroke, a negative MRI result should not be interpreted as excluding stroke. Delayed MRI (three to seven days post-onset) may be required to confirm the presence of a new infarct [8]. Posterior circula- tion stroke should be differentiated from benign peripheral vestibular disorder ( Table 1 ) [8; 10; 18]. Nearly all patients with AVS due to a peripheral cause exhibit nystagmus, which may be inhibited if benzodiazepines/other vestibular sup- pressants are taken before the exam. When possible, assess for nystagmus before medications to manage symptoms are administered [8; 10].
EPISODIC VESTIBULAR SYNDROME Whether intermittent dizziness is triggered or spontaneous, the duration of dizziness episodes (seconds, minutes, hours) is more important than total illness duration. EVS excludes relapsing and remitting symptoms lasting weeks at a time [36]. Triggered EVS Triggered EVS is characterized by brief episodes of dizziness lasting seconds to minutes (depending on etiology), precipi- tated by an obligate trigger. Common triggers are changes in head position or body posture, as when rising from a seated or lying position, tipping the head back to wash one’s hair, or rolling over in bed. Uncommon triggers include loud sounds and the Valsalva maneuver. Patients with nausea or vomiting may overestimate the episode duration, but this can usually be clarified by careful history-taking [8]. As mentioned, clinicians should distinguish triggers from exacerbating features [36]. Prototype t-EVS causes are BPPV and orthostatic hypotension; less commonly, it is caused by superior canal dehiscence syndrome [8]. Possible dangerous causes include central paroxysmal positional vertigo and seri- ous causes of orthostatic hypotension, such as internal bleed- ing. Patients with panic or anxiety disorders may also complain of episodic vertigo, lightheadedness, or dizziness during panic attacks that are triggered or spontaneous. Studies show a high prevalence of vestibular dysfunction for these patients [113].
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Book Code: ANCCTX2027
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