How to Not Miss Posterior Stroke

Written by Thomas Davis

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Follow these five steps to help avoid missing a posterior circulation stroke.

Why does this matter?
Posterior circulation strokes are misdiagnosed 30-60% of the time. Patients with delayed diagnosis may do worse due to extension of the stroke, brainstem compression from posterior fossa edema, or recurrent stroke. 

Keeping Wallenberg straight makes my head spin
Collateral circulation and vascular anatomic variants make it hard to distinguish a lateral medullary stroke (Wallenberg) from a lateral pontine stroke (Marie-Foix).  Instead, this article ditches the eponyms and uses a symptoms-based approach to help you differentiate between a stroke and a non-stroke.

1) Establish an abrupt onset of symptoms.

2) Be cautious with non-specific presentations. Most strokes should present with cranial neuropathies, ocular symptoms, or language deficits. However, vertebral artery dissection can occur with pain only. Also, vomiting may be so severe that it distracts you from looking for associated symptoms.

3) Consider a basilar stroke in altered patients. These patients are obviously ill and will be admitted. But a CTA to expedite timely endovascular intervention may be life saving.  These patients may have involuntary movements that mimic seizure.

4) Use a modern approach to workup dizziness.

  • Asking “What do you mean by dizzy?” isn’t very helpful or evidence based. Instead, focus on “timing and triggers.” It is especially important to recognize that dizziness caused by movement (peripheral etiology) is not the same as dizziness exacerbated by movement, which is more likely to be a central etiology.

  • If dizziness is constant, think:

    • vestibular neuritis, or

    • posterior circulation stroke

  • If dizziness is episodic but triggered, think:

    • BPPV, or

    • orthostatic hypotension

  • If dizziness is episodic and spontaneous, think:

    • vestibular migraine (most common),

    • Meniere’s disease, or

    • TIA

  • A HINTS exam has been shown to be more sensitive than MRI acutely. However, since you’re not a neuro-otologist, supplement your exam with a careful evaluation of the posterior circulation by checking visual fields, cranial nerves, and limb/truncal/gait ataxia.  If anything is abnormal, assume a central etiology.

5) Do not rely over much on imaging. A good physical exam and high index of suspicion are critical.

  • DWI-MRI has a false negative rate of 6.8% among all acute ischemic strokes. This false negative rate increases among patients with posterior circulation strokes (12-18%). It is the highest in patients with small infarcts that are < 10mm in diameter (53%).

  • If you are considering a basilar stroke or vertebral artery dissection, CTA is more available in the ED and may be superior to MRA.

Another Spoonful
We also summarized all eight points of the article in a more detailed summary. It has some additional pearls you need to know.

Source
Avoiding misdiagnosis in patients with posterior circulation ischemia. Acad Emerg Med. 2019 Jul 11. doi: 10.1111/acem.13830. [Epub ahead of print]

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