S2E3: Posterior Circulation Stroke - GEM

Welcome back! Thanks for tuning in to our November episode of TheCase.Report! We’re bringing you our second Geriatric EM episode, and we hope you’ll enjoy this one as much as the first.

For this case, Orla is joined by Deirdre and Lorcán who take us to “dizzying” heights in our latest episode detailing the management of our most complex and common patient cohort.

Our adult in the room is Dr Mustafa Mehmood, an emergency medicine consultant with a special interest in geriatric EM — he’s correcting our homework this month!

We’re also joined by Dr Áine Mitchell, emergency medicine consultant in Sligo University Hospital, who’s here to share some pearls of wisdom on the geriatric emergency department.

Ready? Let’s go!

Posterior Circulation Strokes - Why Are They Different?

Level of disability

Posterior circulation strokes (PCS) account for approximately 20-25% of ischaemic strokes, and have been shown to carry a higher risk of disability compared to anterior strokes at 3 months [1,2]. As we discuss a bit later on, the scales and tools used to identify and score the disability of a stroke often have a larger emphasis on symptoms and signs typical of an anterior circulation stroke.

Presentation

Posterior circulation stroke and TIAs can present differently to anterior strokes, and as we are often the first specialty to see these patients acutely, it is important to keep our clinical suspicion high. One observational study showed that up to 35% of strokes/TIAs were missed when the primary presenting complaint was dizziness, vertigo, or imbalance [3]. Patients presenting with these symptoms constitute a large volume of the workload in the ED - thus accurate diagnosis is key.

Early intervention

Prompt diagnosis and treatment of patients presenting with posterior circulation TIAs can prevent future strokes, highlighting the importance of recognising them.

Shortcomings of Stroke Scales and tools in PCS

So, how do we recognise stroke? There are different instruments available to us to aid in rapid stroke recognition, but the most well-known is probably the Face Arm Speech Test – better known as, FAST!

These scales aren’t infallible, however. Studies have shown FAST misses up to half of PCS, and a negative FAST can lull us into a false sense of security with non-specific symptoms including altered mental status, dizziness and nausea or vomiting often being associated with PCS [4].

National Institutes of Health Stroke Scale (NIHSS)

 This is the most prevalent deficit rating scale for the assessment of acute stroke presentations, but its usefulness has been shown to be limited in PCS.  

In patients presenting with atypical symptoms like headache, vertigo, and nausea and truncal ataxia as the predominant neurologic signs, the NIHSS underestimates the degree of stroke-associated functional impairment [5].     

Posterior Stroke Syndromes

HINTS Assessment

The HINTS (Head-Impulse-Nystagmus-Test of Skew) Assessment is a three-part test used to distinguish central from peripheral causes of vertigo. It’s best used in patients with continuous vertigo. Brain imaging can be normal early in the onset of ischaemic symptoms, meaning the HINTS assessment can be more sensitive in the diagnosis of acute stroke within the first two days of symptom onset [6].

• Head Impulse: Instruct the patient to fix their gaze on a distant target. Turn their head quickly and unpredictably; their eyes should remain on the target. An abnormal response is if the eyes are dragged off target, followed by a saccade back to the initial target. This implies a peripheral vestibular lesion.

• Nystagmus: Peripheral lesions are associated with nystagmus in the same direction, while the nystagmus of central causes change direction with different positions of gaze.

• Test of skew: This involves covering one eye and looking for a vertical shift in the eye when uncovered, which can sometimes indicate a brainstem or cerebellar lesion.

A central lesion is suggested by any of the following:

• Normal head impulse test on both sides

• Direction-changing nystagmus

• Skew deviation

A peripheral lesion is indicated by the presence of all of the following:

• An abnormal head impulse test on one side

• Unidirectional, horizontal, torsional nystagmus that increases in intensity with gaze toward the fast phase

• Absent skew

BIG caveat here though – this test is great to know about, but should always be done by a specialist (a neuro-ophthalmologist) before ruling out a central cause of vertigo.

A few closing tips from our AITR:

Define Dizziness

What does a specific term mean to the patient? Does dizzy mean “the room is spinning around me” (VERTIGO) or does it mean “I feel like I’m going to faint” (PRE-SYNCOPE)? Spend an extra five minutes with the patient to understand what symptoms they are experiencing. It will make you a better clinician and guide you in a better diagnostic direction, ultimately resulting in better patient care!

Beware FAST Pitfalls

Remember, even if the patient is technically FAST negative, they could still be having a stroke. Widen your diagnostic net as much as possible when someone comes in with a “funny turn”.

Patient Selection is Very Important

Special tests – make sure you do the right test for the right patient with the right pathology.

Resources

• 4AT and Delirium workup: http://dementiapathways.ie/permacache/fdd/cf3/d91/f0533608da7160bbe950818bbc5322c6.pdf

• Silver trauma safety net: https://nebula.wsimg.com/6d88552409c14cc17e72e14ecd604243?AccessKeyId=71C7B1EA5618F4C499E1&disposition=0&alloworigin=1

• Medication aids:

  • Parkinson’s medication calculators: https://www.parkinsons.org.uk/professionals/resources/nil-mouth-medication-dose-calculators-and-guidelines

  • Stopp Start: https://academic.oup.com/ageing/article/44/2/213/2812233 article.

  • ACB calculator: http://www.acbcalc.com/

References

1. Merwick, A. and Werring, D., 2014. Posterior circulation ischaemic stroke. BMJ, 348(may19 33), pp.g3175-g3175.

2. Kim, J. et al., 2017. Clinical Outcomes of Posterior Versus Anterior Circulation Infarction With Low National Institutes of Health Stroke Scale Scores. Stroke, 48(1), pp.55-62.

3. Kerber, K., Brown, D., Lisabeth, L., Smith, M. and Morgenstern, L., 2006. Stroke Among Patients With Dizziness, Vertigo, and Imbalance in the Emergency Department. Stroke, 37(10), pp.2484-2487.

4. Hoyer, C. and Szabo, K., 2021. Pitfalls in the Diagnosis of Posterior Circulation Stroke in the Emergency Setting. Frontiers in Neurology, 12.

5. Martin-Schild S, Albright KC, Tanksley J, Pandav V, Jones EB, Grotta JC, et al. . Zero on the NIHSS does not equal the absence of stroke. Ann Emerg Med. (2011) 57:42–5.

6. Kattah, J., Talkad, A., Wang, D., Hsieh, Y. and Newman-Toker, D., 2009. HINTS to Diagnose Stroke in the Acute Vestibular Syndrome. Stroke, 40(11), pp.3504-3510.