Not So Automatic: Why POTS might be more than just an Autonomic Nervous System Disorder
Written by Jane Crosby
Edited by Sam Leyva
September 27th, 2023
Edited by Sam Leyva
September 27th, 2023
Research
You might not have even heard of POTS, but if you have, it’s probably been described as a type of dysautonomia, a dysfunction of the autonomic nervous system. But what if it’s more than this? A review of Postural Orthostatic Tachycardia Syndrome (POTS) by Dr. Svetlana Blitshteyn, Associate Professor of Neurology at the University of Buffalo Jacobs School of Medicine and Director of Dysautonomia Clinic investigates the possibility of Central Nervous System (CNS) involvement.
Clinical criteria for POTS includes a prolonged increase in heart rate of at least 30 bpm in the absence of orthostatic hypotension when transitioning from laying down to standing up as part of a tilt table or 10 minute standing test such as the NASA lean test. Symptoms must also have been present for at least six months. [1,2] The Autonomic Nervous System (ANS) manages involuntary functions such as heart rate, blood, pressure, and digestion, which is why much of POTS is characterized by orthostatic (positional) tachycardia and intolerance, but other symptoms such as headaches, sleep difficulty, dizziness, and brain fog are classic CNS indicators involving the brain and spine at large. These symptoms are generally not relieved by typical POTS treatments targeting ANS symptoms such as increased sodium intake, compression, and beta blockers, a class of medication that slows your heart rate. POTS has many comorbid conditions including Chronic Fatigue Syndrome, small fiber neuropathy, migraine, and Complex Regional Pain Syndrome, which have also recently been thought to be autoimmune in nature or reframed as potential CNS disorders, which has provoked deeper investigation into POTS.
Neuroimaging studies utilizing MRI and MRS have discovered increased amounts of certain messenger compounds as well as lower white matter volume and reduced thickness of the cerebral cortex, the outermost layer of tissue, in the brains of patients with POTS and/or orthostatic intolerance, all of which are CNS differences between POTS patients and healthy controls.[3,4,5] Other findings include pro-inflammatory signaling proteins called cytokines in the Cerebral Spinal Fluid of patients with other autonomic disorders and Chronic Fatigue Syndrome [6, 7], abnormal cerebral blood flow in 100% of POTS patients in one study group [8], and clinical similarities between POTS and another disorder called Spontaneous Intracranial Hypotension in which intracranial pressure drops causing orthostatic headache. Most recently during the pandemic, we have seen patients with post-COVID syndrome and altered permeability of the blood brain barrier present with POTS symptoms.[9] In terms of treatments, POTS patients have shown improvement in response to CNS targeted therapies such as psychotropic medications, central alpha agonists [10], and biofeedback focused on neuroplasticity [11], which, along with the CNS abnormalities found in POTS patients, supports the theory of CNS involvement.
Based on these findings, Dr. Blitshteyn proposes a model in which the pathophysiology of POTS involves both the peripheral and central autonomic nervous systems in which classic POTS theories such as hypovolemia contribute to decreased CSF volume and cerebral blood flow while sympathetic overactivity causes low grade CNS inflammation. [1] The role of structural changes in the brain of POTS patients is still unknown, but is still suggestive of a root in the central nervous system. This model builds on current thinking while investigating holistic effects on, and interactions
within, the entire nervous system. It is plausible to define POTS as a CNS disorder given the array of CNS symptoms patients present with chemical, structural, and functional differences seen on neuroimaging, and positive outcomes from CNS therapies. Further research is needed to confirm Central Nervous System involvement in Postural Orthostatic Tachycardia Syndrome and is definitely worth exploring.
References
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Image Source: “The nervous system” by Brgfx licensed under Freepik License.