When compared to anterior circulation ischemic stroke, the presentation of posterior circulation ischemic stroke (PCIS) is often less obvious, owing to the anatomical and functional complexity of the posterior circulation brain territory. Patients with PCIS may present with vague dizziness, difficulty walking, nausea, or headache without any lateralizing symptoms.¹ This may lead to delays in time-sensitive treatment. Even though PCIS accounts for 15 to 20 percent of all stroke events, it is three times more commonly missed in emergency departments (EDs) compared to anterior strokes with up to 10 percent being missed on the first ED visit.^2,3 Yet, systematic reviews suggest that outcomes with intravenous thrombolysis are at least as good as with anterior circulation strokes with a lower risk of intracranial hemorrhage, while comparable.^4–6 It is therefore incumbent upon the EM physician to make their best effort to identify patients with posterior circulation stroke in a timely manner so that those who fulfill criteria for emergency treatment such as endovascular therapy or intravenous thrombolysis can be optimized to improve outcomes. I outline some key clinical clues to help identify patients with posterior circulation stroke.

Understanding the Anatomy

An understanding of the vascular anatomy can help recall the symptoms of posterior circulation stroke. The vertebral arteries, cerebellar arteries, and posterior cerebral arteries supply the brainstem, cerebellum, and occipital lobes. Brainstem deficits include unilateral limb weakness, sensory loss, cranial nerve palsies, and altered level of awareness (including locked-in syndrome. Cerebellar features include vertigo, truncal, limb ataxia, and nystagmus. Occipital lobe features include visual field deficits.

The most common symptoms of PCIS based on registry data are dizziness (47 percent), unilateral weakness (41 percent) dysarthria (31 percent), gait ataxia (31 percent), headache (28 percent), nausea and vomiting (27 percent), and nystagmus (24 percent).¹ One easy way to remember the clinical features of PCIS is the “Dangerous Ds” memory aid: diplopia, dysarthria, dysphagia, dysdiadochokinesia, dysmetria, dystaxia, and dysphonia. While observational data suggest that isolated vertigo is rare in patients with PCIS, it may be that clinical assessment is simply not thorough enough to detect additional clinical findings.⁷ A detailed history and physical are imperative, paying close attention to three things: risk factors, cranial nerve dysfunction, and gait.

First, risk factor assessment: A key risk factor for PCIS is atrial fibrillation, especially in patients who are not anticoagulated for stroke prevention. In fact, a cardioembolic cause (predominantly as a result of atrial fibrillation) is the most common etiology of PCIS, ahead of atherosclerosis and arterial dissection.⁸ Traditional cardiovascular risk factors should also be taken into account. Unusual neck pain that lacks features of musculoskeletal injury, especially if it presents after recent head or neck trauma, should raise the suspicion for a vertebral artery dissection, especially in young adults with any PCIS symptoms.

The second aspect of clinical assessment that is important is the cranial nerve exam, including a focused eye exam. Four of the “Dangerous Ds” to keep in mind as part of the cranial nerve exam are diplopia, dysarthria, dysphagia, and dysphonia. Ptosis may indicate Horner’s Syndrome which, in one study, had the highest predictive value for a diagnosis of PCIS.⁹ Visual fields should be scrutinized for any deficits and extra-ocular movements (EOMs) should be assessed for the possibility of locked-in syndrome. This is a rare presentation of basilar artery occlusion that paralyzes all peripheral motor function except those that control EOMs. In patients who present after a sudden collapse with persistent loss of consciousness and paraplegia with no clear alternative cause, locked-in syndrome should be considered, and EOMs assessed for sparing. Patients with locked-in syndrome may also have hemodynamic instability and cardiac dysrhythmias secondary to massive catecholamine surge associated with massive brain insult. Suffice to say that a focused eye exam may reveal a finding that increases one’s suspicion of PCIS in a patient with an otherwise benign clinical presentation for stroke.

The third aspect of clinical assessment that is important in assessing for PCIS is gait. It is imperative to walk test dizzy patients to assess for truncal ataxia. One clinical pearl is that the vertigo in patients with PCIS tends to be less severe than that in peripheral causes of vertigo, while the ataxia in patients with PCIS tends to be more severe than in patients with a peripheral cause of vertigo. Do not let mild vertigo symptoms sway you away from a diagnosis of PCIS. While much has been written about the bedside head-impulse nystagmus test-of-skew (HINTS) exam for ruling in a central cause of vertigo, observational data suggests that EM physicians are very poor at performing this exam, so that the test is not sufficiently accurate to rule out PCIS and may falsely reassure clinicians that PCIS is not present.¹⁰ Despite a meta-analysis suggesting a 15-fold increased risk for PCIS in patients with a positive HINTS tests, in this author’s opinion the HINTS exam should not be relied on to help make emergency treatment decisions for patients who present with PCIS symptoms.¹¹

Next time you are faced with a patient who presents with the chief complaint of dizziness, consider PCIS in your differential diagnosis and be sure to assess for risk factors, cranial nerve abnormalities (including a focused eye exam), and gait. If there are one or more worrisome features, consider speaking to your local stroke neurologist for consideration of intravenous thrombolysis or endovascular therapy as per your local protocol.

A special thanks to Dr. Katie Lin for her expertise in the EM Cases podcast that inspired this article.

Dr. Helman is an emergency physician at North York General Hospital in Toronto. He is an assistant professor at the University of Toronto, Division of Emergency Medicine.

References

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