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POTS vs. IST: A Detailed Look Through the Lens of Functional Neurology

Tachycardia, dizziness, fatigue, pain, shortness of breath, anxiety and more can all be symptoms of a condition called Postural Orthostatic Tachycardia Syndrome (POTS) and they can also be symptoms of a condition called Inappropriate Sinus Tachycardia (IST). So, what is the difference?


The diagnosis of IST is a diagnosis of exclusion, which means that other conditions and causes need to be ruled out. If there is no known cause for these symptoms, IST is characterized by its symptoms of a resting heart rate elevated above 100 beats per minute (bpm) with an average 24-hour heart rate over 90bpm. The tachycardia in IST is often associated with palpitations.

A diagnosis of POTS requires the diagnostic criteria of an increase in heart rate, for the adult population, of 30 bpm from supine (lying face up) to standing or 40 bpm in the adolescent population.

What We See Clinically

At CFNC we see patients with many different forms of dysautonomia, with POTS and IST being among the most common. While these conditions present very similarly from a symptom perspective, the diagnostic criteria is different and we usually find that the dysfunction of the nervous system is also different.

While the symptoms for many dysautonomia cases involve the cardiovascular system, the underlying root causes lie in the communication between the brain and cardiovascular system to provide proper information for normal vitals. There is a subset of cases that present with structural abnormalities in the cardiovascular system that also play a major role and these patients can also benefit from improved neuro-cardiac communication.

When evaluating patients at CFNC, our doctors have found a significant trend in functional neurological abnormalities for these conditions.

In the cases of IST, it is often seen that the dysfunction in the brain is concentrated in the mesencephalon or midbrain. This area of your brainstem is responsible for many functions including but not limited to pain modulation, consciousness, sleep rhythms, pupillary responses, eye movements, DOPAmenergic and GABAergic centers.

Your midbrain is in constant communication with your limbic centers, cortex, sympathetic ganglion and more. It is no wonder why dysfunction of this part of our brain could lead to increased heart rate and anxiety! Yes, you read that correctly – dysfunction in this part of your brain could cause you to experience anxiety NOT that you have anxiety and that is the only reason you have all of these symptoms.

With POTS, we find neurological dysfunction often resides in the pontomedullary areas of the brainstem and can produce very similar symptoms. The pontomedullary area of your brainstem is responsible for eye movements, motor and sensory control to the face, sound conduction, swallowing, taste and coordination to the tongue and throat, and motor control of some neck muscles.

Both your midbrain and your pontomedullary regions communicate with your hypothalamus which is responsible for relayed communication from the nervous system to the endocrine system! This is where we find an overlap in these conditions through hypothalamic-pituitary-adrenal dysfunction! We don’t mean this in the context of adrenal disorders like Addison’s or Cushing’s disease, but more in disruption of your sleep wake cycles and hormones further leading to complication of both symptoms and neurological function. (Check out our blog post highlighting the cross-talk between the nervous, immune and endocrine systems.)

Our Purpose

Our providers at Carolina Functional Neurology Center work to provide the most comprehensive treatment for all of our patients. We hope this blog provides you with some helpful information if you are dealing with POTS or IST. At CFNC, we look further at your neurological and endocrine function, and with the right combination of therapy, nutrition, supplementation and lifestyle changes we think everyone can improve their symptoms and live a more functional life!

If you are interested in speaking with one of our doctors about your symptoms please contact us.

DISCLAIMER: This information is intended to be informational and informative solely based on the clinical experience of our doctors at CFNC. Our goal is to increase awareness of these conditions for treatments and research. This is not intended to be medical advice, if you are experiencing any of these symptoms or conditions please contact your healthcare provider.


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