Family 8: Autonomic and Peripheral Nervous System
Family overview. The autonomic nervous system regulates cardiovascular, respiratory, digestive, and thermoregulatory homeostasis through sympathetic and parasympathetic branches. Small unmyelinated C-fibres and thinly myelinated AΞ΄-fibres convey autonomic signals and nociception; their structural loss constitutes small fiber neuropathy (SFN).
Concrete mechanisms and ME/CFS evidence:
Baroreflex failure. Impaired baroreceptor-mediated heart rate and blood pressure regulation; reduced heart rate variability; impaired beat-to-beat blood pressure control.
Postural orthostatic tachycardia syndrome (POTS). Excessive heart rate increase (β₯30 bpm) on standing; neurally mediated hypotension variants; present in a large ME/CFS subset. Driven by hypovolemia, adrenergic autoantibodies (Family 5), and SFN-mediated microvascular dysregulation.
Catecholamine dysregulation. Elevated basal catecholamines with blunted acute stress response; chronic catecholamine exposure induces Ξ²2-AR downregulation and T cell metabolic suppression and exhaustion (linking to Family 4).
Small fiber neuropathy (SFN). Reduced intraepidermal nerve fiber density (IENFD) on skin biopsy in ~one-third of ME/CFS patients; C-fiber dysfunction demonstrated by reduced heat detection thresholds (Giannoccaro et al. 2021). SFN damages autonomic fibers innervating microvasculature, impairing exercise-related blood flow redistribution.
Neurovascular dysregulation via SFN. Damaged autonomic fibers cause inappropriate vasodilation and oxygenated blood shunting away from exercising muscle, contributing to exercise intolerance via a peripheral mechanism distinct from central fatigue or deconditioning.
Impaired vagal tone. Reduced parasympathetic activity; blunted vagal anti-inflammatory reflex may contribute to chronic immune activation (Tracey 2002). In Long COVID, this functional deficit is accompanied by structural evidence of selective cholinergic (VIP+) denervation of the gastric mucosa correlating with reduced vagal HRV (Acanfora et al. 2026), though whether comparable structural fiber loss occurs in ME/CFS is not yet established (Structural Vagal Cholinergic Denervation as an Anatomical Substrate for Post-Viral Dysautonomia and Sustained Inflammation).
Full discussion: Cardiovascular Dysfunction and Neurological and Neurocognitive Dysfunction.
Evidence status: Established (POTS, baroreflex, and SFN independently replicated; IVIG response in SFN subgroup supports pathogenic role).