• Austin Brook

The Dizziness Differential

Let’s start this blog off with a patient scenario. A 27-year-old male gets home from the gym following a high-intensity workout. He takes no supplements, has no history apart from childhood asthma, and is not currently taking any medications. After talking to his neighbor for 15 or so minutes he goes inside to take a shower. He gets out of the shower and reaches to turn off the light switch when he notices the double light switch has turned into a single. He closes his left eye and focuses on his right index finger. Suddenly all but his index finger have faded away. When closing his right eye fixating on his left pinky finger, all fingers to the right are mysteriously missing. Anxiously, he goes back and forth between the light switch and his hand before telling his wife… “Something is really wrong, I think I am having a stroke”.

We as clinicians are accustomed to diagnosing our friends, families, neighbors, and even pets with an array of outlandish conclusions. I for one never would have guessed that at 27 years old I would be standing in my hallway self-diagnosing a posterior circulation stroke. Julius Caeser is famed for coining the phrase “Ut est rerum omnium magister usus” or “Experience is the teacher of all things”. In sharing my experience, I hope that we can all gain valuable knowledge and not miss what may be right in front of us.

Posterior Circulation Strokes (PCS) account for roughly 25% of all ischemic strokes though they are infrequently recognized by EMS and ED clinicians due to their cloaked and vague symptomatology (Hoyer & Szabo). With no shortage of prehospital stroke scales (CPSS, RACE, FAST, LAMS, VAN, and more) why are we frequently missing as many as 25% of ischemic strokes? We miss them because we aren’t looking for them. It reminds me of the classic video where a group of people is passing a basketball back and forth. The audience is told to focus exclusively on the people wearing white shirts. Halfway through the clip, someone in a gorilla costume walks center screen and most of us never see it happen until they later go back and tell us to look for it. While it may seem preposterous that the majority of people miss a 6-foot gorilla in the middle of a basketball game, we do. This is a measurement of our selective attention and is a form of cognitive bias called anchoring. For those who haven’t seen the clip, check it out at bit.ly/3IliMLO. The stroke scales that we use work in conjunction with our selective attention. They are not designed to identify a stroke as much as they are designed to quickly quantify the potential severity and point us to the correct receiving destination. If clinicians don’t first recognize that a stroke is on the differential, then the scale is likely not utilized.

A word on anchoring bias

Cognitive bias is a steady topic of conversation in clinical and academic circles. Since publishing To Err is Human: Building a Safer Health System in 2000, many other authors have come out with works that analyze the way people think and make decisions. Perhaps one of the most notable is the book Thinking Fast and Slow by Daniel Kahneman. These

resources are both available below, and I encourage all emergency clinicians to give them a look. Anchoring bias is aptly named as clinicians rely heavily on the initial information presented to them, inadvertently lumping new information as links on the chain that holds tight to the anchor in place. Considering all possibilities and maintaining a wide differential is vital to pursue all possibilities before us.

Anatomy Review

Perfusion of the brain is done by two paralleled pathways, the carotid, and vertebral arteries. The anterior cerebrum receives its flow from the carotid arteries, and the vertebral arteries supply the posterior cerebrum, cerebellum, midbrain, thalami, and brainstem. The carotid arteries supply approximately 80% of blood flow to our brain, and the vertebral arteries handle the other 20%. If we compare that to our incidence of posterior circulation strokes, it makes sense that they would account for 20-25% of all ischemic strokes as they receive a similar percentage of the brain's flow. When determining what is considered anterior and posterior, the most popular definition is carotids supply anterior and vertebral arteries supply posterior.

Now picture your classic stroke patient as captured by one of our prehospital scales. Facial droop, unilateral arm and leg weakness, and slurred speech are likely symptoms. These functions all occur in the anterior portion of the brain, pictured below. Areas in blue here

represent our speech and gross motor functions. Seated just behind that in red are our sensation and language comprehension. We fail to capture symptoms that manifest from a CVA in any of the areas not highlighted. As much as 50% of the brain's function is not accounted for in our prehospital measurements of stroke.

In the case of posterior infarcts or bleeds, symptoms such as dizziness, vision changes, dysarthria (rather than aphasia), balance and gait disturbances, and swallowing problems are common. To capture these symptoms, hospitals transitioned from FAST (Face, Arms, Speech & Time) to BEFAST, incorporating balance and eyes to the assessment. The BEFAST remains the only rapid stroke assessment I am aware of that includes symptomatology suggestive of a posterior circulation vascular compromise. If anyone out there is aware of others, let me know!

Stroke diagnosis in the prehospital environment relies exclusively on astute symptom recognition. Though mobile cat scan technology is on the rise, it is far from prudent in most systems worldwide. So how can prehospital improve their recognition of nearly 25% of all strokes? Learn the symptoms and consider posterior circulation infarct in the differential. After today, three patient categories that we see almost daily should raise a new set of red flags. The New England Medical Center has a registry of posterior circulation CVAs, and they report that of patients diagnosed with these strokes, the most common vague differential symptoms were dizziness (47%), headache (28%), and nausea or vomiting (27%). I don't know how many of you work in an emergency department, but I never worked a shift where at least one of these symptoms was reported by patients.

It is unreasonable and costly to work up every one of these symptoms for a stroke every time, so there needs to be a bit of discipline when applying this information. Use it to aid in priming on the way to your next call and consider other signs, symptoms, and stories that may warrant a deeper look into an otherwise simple complaint. The system I learned in the stroke center I worked for was called "The Five Ds," consisting of dizziness PLUS dystaxia, dysarthria, dysphagia, or diplopia. When the latter are reported in the presence of dizziness, the sensitivity for posterior circulation strokes climbs dramatically.

Receiving Destinations

Even without expensive CT scanners, prehospital clinicians have an excellent opportunity to reduce the morbidity and mortality associated with strokes by getting patients to the correct receiving facility. Symptom recognition is only half the battle; choosing the appropriate facility is the other half. I live in California, where we classify stroke centers as primary and comprehensive centers. The individual differentiation is based on the services provided, comprehensive centers offering mechanical thrombectomy (clot removal). I understand that similar classifications are growing in popularity nationwide, and I would love to hear from you all about what your local communities offer! I often hear one statement from prehospital providers: "if comprehensive centers offer better services, we should take all patients there." While this seems like a reasonable enough conclusion, I hope to shed a little light on why the differentiations exist. Primary stroke centers offer patients a chance to receive chemical thrombolysis in the form of alteplase, retavase, or tenecteplase. These life-saving medications are incredibly time-sensitive, and in some cases, minutes truly matter. Time spent diverting to a comprehensive center can cost the patient their opportunity at chemical thrombolytics. While comprehensive centers do offer mechanical clot removal, an even smaller subset of patients meet the criteria for this procedure as it requires a large clot in a somewhat proximal artery, typically described as emergent large vessel occlusions (ELVO). Prehospital stroke scales like the Los Angeles Motor Score (LAMS) or VAN (vision, aphasia, neglect) are great for determining when an ELVO might be present. Without a doubt, patients meeting the criteria for ELVO's should go to a comprehensive center but, taking every patient with stroke symptoms to a comprehensive center will overload that resource and is potentially costly on neurologic outcomes.

Posterior circulation strokes present a different conundrum. The question is not primary vs. comprehensive, but the most accessible receiving hospital versus primary. Are you confident enough to bypass the closest hospital for a stroke center for a vague complaint such as dizziness or nausea/vomiting? That takes far more clinical gestalt, in my opinion. I hope you can take some time now to piece out the symptoms in front of you, so you can catch what you may not see at first.

Lessons from my experience

Many elements of the evening of my stroke fell into place and contributed to my fortunate outcome. Following nursing school, in September of 2018, I was hired into my local community ED in a suburb of Los Angeles, California. As a primary stroke center, ED nurses received annual training alongside the local fire department, updated on evidence in stroke care. The heavy-pressed stroke topic of my last year in this hospital was posterior strokes and how to catch them because, unfortunately, they were being missed too often.

Following the onset of my symptoms, I assumed that a stroke couldn't be the likely cause. I gave it about 2 min before I was so freaked out by the persistence of blindness that I had my wife take me in. On the way to the hospital, I was faced with the same dilemma… primary center (10 min) or comprehensive (20 min). I decided to go with the closest option for a few reasons: proximity. The second reason being I knew the staff and could comfortably advocate for myself a little more aggressively. The final reason was I wasn't sold on the reality that this was a stroke, and I didn't want to waste time driving to a comprehensive center only to look completely unknowledgeable.

I'll admit even arriving at the ED staffed with friends; It was a hard sell to convince them to activate the code stroke. It took running into a physician friend, describing my symptoms to him, and then He insisting they activate. I got the CT angio of the brain showing a P3 segmental occlusion of the posterior cerebral artery and then discussed it with the ED physician and neurologist. Their recommendation was for tenecteplase as they had already spoken with the leading interventional neurologist in our area. In my case, mechanical thrombectomy wasn't even an option available given the location of the clot. I admit I fearfully accepted the tenecteplase and waited anxiously for the results… will I bleed out into my skull? Thankfully all was well, and my symptoms resolved within 15 minutes. The following morning, I got a brain MRI that showed the infarct's complete resolution with no residual deficits.

I am so grateful to the fantastic staff of physicians, nurses, and techs that saved my vision and allowed me to keep doing what I love. However, with this experience behind me, I had an unexpected opportunity for introspection. Would I have advocated as hard as I did, had the patient been a stranger? Would I have trusted my gut enough to put my reputation on the line for a symptom as vague as blind spots, dizziness, or even a headache? I don't know what I would've done before all this, but having been through it myself, I can guarantee that I keep posterior circulation strokes on my differential. I hope this encourages you to do the same.


Hoyer, C., & Szabo, K. (2021). Pitfalls in the Diagnosis of Posterior Circulation Stroke in the Emergency Setting. Frontiers in neurology, 12, 682827. https://doi.org/10.3389/fneur.2021.682827

Institute of Medicine (US) Committee on Quality of Health Care in America, Kohn, L. T., Corrigan, J. M., & Donaldson, M. S. (Eds.). (2000). To Err is Human: Building a Safer Health System. National Academies Press (US).

Kahneman, D. (2011). Thinking, fast and slow. Farrar, Straus and Giroux.

Searls, D. E., Pazdera, L., Korbel, E., Vysata, O., & Caplan, L. R. (2012). Symptoms and signs of posterior circulation ischemia in the new England medical center posterior circulation registry. Archives of neurology, 69(3), 346–351. https://doi.org/10.1001/archneurol.2011.2083