Pathophysiology of Myalgic Encephalomyelitis/Chronic Fatigue Syndrome
Myalgic Encephalomyelitis/Chronic Fatigue Syndrome (ME/CFS) is a multisystem neuroimmune illness characterized by immune dysregulation, mitochondrial dysfunction, vascular and endothelial abnormalities, neuroinflammation, and autonomic nervous system dysfunction, typically triggered by viral or bacterial infections 1.
Core Pathophysiological Mechanisms
Immune System Dysfunction
The immune system shows consistent abnormalities across multiple domains:
- Diminished natural killer cell function - a hallmark finding that impairs viral surveillance 1
- T cell exhaustion and other T cell abnormalities - reflecting chronic immune activation 1
- Reactivated herpesviruses including Epstein-Barr virus (EBV), HHV-6, HHV-7, and cytomegalovirus 1
- Immune and metabolic system dysregulation that persists long after the initial infectious trigger 2
Mitochondrial and Metabolic Dysfunction
Energy production at the cellular level is fundamentally impaired:
- Mitochondrial dysfunction with loss of mitochondrial membrane potential 1, 3
- Exercise intolerance with impaired oxygen consumption and reduced anaerobic threshold 1
- Altered metabolic profiles including dysfunctional usage of fatty acids and amino acids 1
- Dysfunctional mitochondrion-dependent lipid catabolism contributing to exercise intolerance 1
- Redox imbalance and oxidative stress 1
Vascular and Endothelial Abnormalities
Circulatory dysfunction appears central to symptom generation:
- Deformed red blood cells and reduced blood volume 1
- Endothelial dysfunction affecting tissue perfusion 1
- Microclots and hyperactivated platelets 1
- Reduced cerebral blood flow correlating with fatigue severity 1
An autoimmune hypothesis suggests that autoantibodies against β2-adrenergic receptors and M3 acetylcholine receptors cause vasoconstriction and hypoxemia, as both receptors are important vasodilators. This impaired circulation and oxygen supply could explain muscular and cerebral hypoperfusion documented in multiple studies 4.
Neurological Dysfunction
The central and autonomic nervous systems show widespread abnormalities:
- Neuroinflammation with microglial activation 1
- Brainstem abnormalities affecting autonomic regulation 1
- Elevated ventricular lactate levels suggesting metabolic stress 1
- Hypothalamus-pituitary-adrenal axis dysfunction with low cortisol levels not compensated by increased ACTH 1
- Abnormal eye and vision findings including corneal nerve fiber loss 1
Autonomic Nervous System Dysregulation
Many patients develop orthostatic intolerance and postural orthostatic tachycardia syndrome (POTS), reflecting dysautonomia that overlaps significantly with ME/CFS pathophysiology 2.
Infectious Triggers and Viral Persistence
ME/CFS onset follows viral or bacterial infections in the majority of cases 1:
- Common triggering pathogens: EBV, Coxiella burnetii (Q fever), Ross River virus, West Nile virus, and SARS-CoV (27.1% of survivors met ME/CFS criteria at 4 years) 1
- Post-infectious mechanism: The direct link between infection and prolonged symptoms often remains unclear, but immune dysregulation with or without pathogen reactivation appears central 2
Clinical Implications of Pathophysiology
The pathophysiological findings explain the cardinal symptom of postexertional malaise - a worsening of symptoms following physical or cognitive exertion. This reflects the combination of:
- Impaired oxygen extraction and utilization
- Mitochondrial dysfunction preventing adequate ATP production
- Vascular abnormalities limiting tissue perfusion
- Immune activation triggered by metabolic stress
Important caveat: ME/CFS remains poorly understood despite these documented abnormalities, with relatively few practitioners experienced in recognizing these pathophysiological patterns 2. The heterogeneity of symptom presentation and precipitating events suggests that different causes may initiate similar body-wide pathological cascades 5.
The overlap with Long COVID is striking - approximately 50% of Long COVID patients meet ME/CFS criteria, and both conditions share similar haemodynamic, symptomatic, and cognitive abnormalities 1. This suggests common pathophysiological mechanisms across post-infectious syndromes.