Medically unexplained symptoms: polyvagal theory to explain the weird things we see

Bruce Arroll is a Professor of General Practice at the University of Auckland and a GP at the Greenstone Family Clinic in Manurewa Auckland


My first clinical impression of primary care was of lots of symptom clusters that did not appear in Harrisons Textbook of Medicine. These symptoms would fluctuate and I would investigate some and often find no satisfactory answers from my investigations and referrals. I gradually learned to use time as my diagnostic test and some of these symptoms would disappear while others would stay. Many of them did not follow any anatomical or physiological pattern. I now prefer the term illness without disease1 as Medically Unexplained Symptoms (MUS) sounds like if you did just one more (or the right) scan/xray/referal/consultation you'd find the answer. There was a qualitative study on what patients liked when they had MUS. Their preference was for some sort of explanation and I now use the narrative “ I don’t have a name for what you are presenting with but I think the best explanation is that you have a short circuit and one day we may have an explanation for this.” This turned out to be prophetic because I now think that I have a (potential) answer to MUS and it revolves around electricity or at least the functioning of the sympathetic and central nervous system.

I had the good fortune recently to  meet Joel and Michelle Levey who were early proponents of mindfulness in Group Health in Seattle in the 1970s. Joel made a comment about the balance of the sympathetic and parasympathetic nervous system and mentioned the Polyvagal theory of Stephen Porges who reports three autonomic nervous systems rather than the two traditionally described. I started to think of the Sympathetic and Parasympathetic nervous systems (SNS and PSNS) , and the central nervous system, and their role in “MUS” or weird symptoms. My theory is that MUS are caused by the partial misfiring of the SNS, PSNS and the central nervous system. This would explain why these seem to occur more often in patients who are stressed and anxious and why their symptoms do not fit a disease model. It also explains why many of these MUS such as fibromyalgia, chronic pain and chronic fatigue all seem to respond (in part) to anti-depressant medication, psychological therapies, mindfulness and exercise.

A measure of vagal “health” is respiratory sinus arrhythmia (RSA) i.e. beat to beat variation (as in fetal monitoring). Porges showed patients, with Borderline personality disorder, films with variable emotional content and found the RSA progressively decreased in the borderline group, while RSA progressively increased (a more peaceful outcome) in the control group. By the end of the experiment, the groups differed significantly on both RSA and heart rate. I found the Porges book difficult to follow but the concept is explained in a blog by Tim Vaughan which I have summarised in the table below. I have added an additional row where I speculate about some of the mental health categories that could be associated with each part of the autonomic nervous system.

The three (not two) autonomic nervous systems

Oldest system Next oldest Newest
Myelination of vagus Unmyelinated Unmyelinated Sympathetic –adrenal nervous system. (SANS) Myelinated

Unique to mammals –linked to adrenal system, heart and muscles of face.

Physiological role Extends below the diaphragm in threat situations and, in humans, causes immobilisation. When there is threat -> fight/flight i.e. hypervigilance, and blood pressure rises The vagal brake modulates the heart rate. Under threat this stops and allows (SANS)
Speculated Possible clinical syndromes Depression

Chronic fatigue syndrome.

Potentially lethal / catatonic states and anorexia nervosa

Chronic pain




Calm visceral states


Stops chronic pain by modulating unmyelinated vagus

We need to start thinking in terms of the narrative,

“too much accelerator and not enough brake... we don’t have a name for what you have but your electrical system is out of balance.”

I find patients like this analogy and welcome advice to exercise more and consider mindfulness. We should at least use time as the diagnostic test rather than hit the panic button and search for serious illness with investigations and/or referral at the first presentation of MUS. Equipment to measure RSA is becoming more affordable and it may become a standard piece of equipment in the medical office. A positive diagnosis of a “short circuit” could potentially reduce or delay the many colonoscopies and gastroscopies for gastrointestinal symptoms, head scans for headaches and ECG/cardiac enzymes for chest pain. This may be a way of reducing the too-much-medicine that occurs in modern clinical practice.


  1. Wilson H, Cunningham W. Being a Doctor Understanding Medical Practice: Published by Otago University Press PO Box 56 / Level 1, 398 Cumberland Street,Dunedin, New Zealand, 2013

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