Chronic Fatigue: Etiology
Clinical Description of the Etiology of Chronic Fatigue Syndrome (ME/CFS)
Myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) is a complex, chronic, multisystem medical condition characterized by persistent, functionally impairing fatigue lasting longer than six months that is not relieved by rest and is accompanied by post-exertional malaise, cognitive dysfunction, sleep disturbance, and autonomic symptoms. Current evidence indicates that ME/CFS does not result from a single cause but reflects interacting neuroimmune, neuroendocrine, autonomic, and metabolic dysregulation. The disorder is best conceptualized as a condition of impaired physiologic energy production and recovery rather than reduced motivation or psychological weakness.
Neuroimmune and inflammatory mechanisms
Research suggests persistent immune activation, including elevated pro-inflammatory cytokines and altered immune signaling. Many cases begin after viral or infectious illness, supporting a post-infectious or immune-triggered process. Chronic inflammation may produce “sickness behavior” symptoms such as malaise, fatigue, cognitive slowing, and reduced activity tolerance.
HPA axis dysregulation
Altered hypothalamic–pituitary–adrenal (HPA) axis function and abnormal cortisol rhythms are commonly observed. Dysregulated cortisol output may impair wakefulness, stress tolerance, and metabolic efficiency, contributing to non-restorative sleep and persistent exhaustion.
Autonomic nervous system dysfunction
Autonomic irregularities, including orthostatic intolerance, heart rate variability abnormalities, and sympathetic overactivation, are frequently reported. These changes may impair circulatory stability and oxygen delivery, resulting in dizziness, weakness, and post-exertional symptom exacerbation.
Mitochondrial and metabolic impairment
Emerging findings suggest reduced cellular ATP production and impaired mitochondrial energy metabolism. This inefficiency may explain the hallmark feature of post-exertional malaise, in which even minor physical or cognitive effort leads to disproportionate fatigue and prolonged recovery.
Sleep architecture disruption
Patients commonly experience non-restorative or fragmented sleep with reduced slow-wave and REM sleep. Poor sleep quality worsens pain sensitivity, mood regulation, and cognitive clarity, perpetuating daytime fatigue.
Neurochemical alterations
Changes in dopamine and norepinephrine regulation may reduce motivation, sustained attention, and cognitive stamina. These disruptions overlap with executive dysfunction and “brain fog,” contributing to impaired functional capacity.
Trauma, PTSD, and chronic stress
Chronic stress or trauma exposure may sensitize stress-response systems, contributing to sustained autonomic arousal, inflammatory signaling, and endocrine disruption. This physiologic load can maintain fatigue even when external stressors are reduced, suggesting a trauma-related perpetuating mechanism in some individuals.
Behavioral and psychosocial maintenance factors
Although ME/CFS is not a psychiatric condition, secondary factors such as deconditioning, disrupted routines, avoidance of activity due to symptom flares, and comorbid anxiety or depression may worsen functional impairment. These are considered maintaining factors, not primary causes.
Medical rule-outs
Differential diagnosis should include anemia, thyroid disease, sleep apnea, nutritional deficiencies, medication effects, and other systemic illnesses that may mimic or worsen fatigue.
Myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) is a complex, chronic, multisystem medical condition characterized by persistent, functionally impairing fatigue lasting longer than six months that is not relieved by rest and is accompanied by post-exertional malaise, cognitive dysfunction, sleep disturbance, and autonomic symptoms. Current evidence indicates that ME/CFS does not result from a single cause but reflects interacting neuroimmune, neuroendocrine, autonomic, and metabolic dysregulation. The disorder is best conceptualized as a condition of impaired physiologic energy production and recovery rather than reduced motivation or psychological weakness.
Neuroimmune and inflammatory mechanisms
Research suggests persistent immune activation, including elevated pro-inflammatory cytokines and altered immune signaling. Many cases begin after viral or infectious illness, supporting a post-infectious or immune-triggered process. Chronic inflammation may produce “sickness behavior” symptoms such as malaise, fatigue, cognitive slowing, and reduced activity tolerance.
HPA axis dysregulation
Altered hypothalamic–pituitary–adrenal (HPA) axis function and abnormal cortisol rhythms are commonly observed. Dysregulated cortisol output may impair wakefulness, stress tolerance, and metabolic efficiency, contributing to non-restorative sleep and persistent exhaustion.
Autonomic nervous system dysfunction
Autonomic irregularities, including orthostatic intolerance, heart rate variability abnormalities, and sympathetic overactivation, are frequently reported. These changes may impair circulatory stability and oxygen delivery, resulting in dizziness, weakness, and post-exertional symptom exacerbation.
Mitochondrial and metabolic impairment
Emerging findings suggest reduced cellular ATP production and impaired mitochondrial energy metabolism. This inefficiency may explain the hallmark feature of post-exertional malaise, in which even minor physical or cognitive effort leads to disproportionate fatigue and prolonged recovery.
Sleep architecture disruption
Patients commonly experience non-restorative or fragmented sleep with reduced slow-wave and REM sleep. Poor sleep quality worsens pain sensitivity, mood regulation, and cognitive clarity, perpetuating daytime fatigue.
Neurochemical alterations
Changes in dopamine and norepinephrine regulation may reduce motivation, sustained attention, and cognitive stamina. These disruptions overlap with executive dysfunction and “brain fog,” contributing to impaired functional capacity.
Trauma, PTSD, and chronic stress
Chronic stress or trauma exposure may sensitize stress-response systems, contributing to sustained autonomic arousal, inflammatory signaling, and endocrine disruption. This physiologic load can maintain fatigue even when external stressors are reduced, suggesting a trauma-related perpetuating mechanism in some individuals.
Behavioral and psychosocial maintenance factors
Although ME/CFS is not a psychiatric condition, secondary factors such as deconditioning, disrupted routines, avoidance of activity due to symptom flares, and comorbid anxiety or depression may worsen functional impairment. These are considered maintaining factors, not primary causes.
Medical rule-outs
Differential diagnosis should include anemia, thyroid disease, sleep apnea, nutritional deficiencies, medication effects, and other systemic illnesses that may mimic or worsen fatigue.
References (APA 7th Edition)
Brosschot, J. F., Verkuil, B., & Thayer, J. F. (2017). Generalized unsafety theory of stress: Prolonged autonomic stress activation and health consequences. Neuroscience & Biobehavioral Reviews, 74, 287–296. https://doi.org/10.1016/j.neubiorev.2016.11.001
Cleare, A. J. (2004). The HPA axis and the genesis of chronic fatigue syndrome. Trends in Endocrinology & Metabolism, 15(2), 55–59. https://doi.org/10.1016/j.tem.2003.12.002
Institute of Medicine. (2015). Beyond myalgic encephalomyelitis/chronic fatigue syndrome: Redefining an illness. National Academies Press. https://doi.org/10.17226/19012
Jason, L. A., Sunnquist, M., & Brown, A. (2015). Chronic fatigue syndrome: Diagnostic criteria reconsidered. Journal of Clinical Psychology, 71(5), 466–479. https://doi.org/10.1002/jclp.22174
McEwen, B. S., & Akil, H. (2020). Revisiting the stress concept: Implications for affective disorders. Journal of Neuroscience, 40(1), 12–21. https://doi.org/10.1523/JNEUROSCI.0733-19.2019
Pace, T. W. W., & Heim, C. M. (2011). A short review on the psychoneuroimmunology of chronic fatigue syndrome. Brain, Behavior, and Immunity, 25(1), 7–13. https://doi.org/10.1016/j.bbi.2010.06.003
VanElzakker, M. B., Brumfield, S. A., & Lara Mejia, P. S. (2019). Neuroinflammation and cytokines in chronic fatigue syndrome. Frontiers in Psychiatry, 10, 102. https://doi.org/10.3389/fpsyt.2019.00102
Yehuda, R., & LeDoux, J. (2007). Response variation following trauma: A translational neuroscience approach to PTSD. Neuron, 56(1), 19–32. https://doi.org/10.1016/j.neuron.2007.09.006
Walker, M. P. (2017). Why we sleep: Unlocking the power of sleep and dreams. Scribner.
Brosschot, J. F., Verkuil, B., & Thayer, J. F. (2017). Generalized unsafety theory of stress: Prolonged autonomic stress activation and health consequences. Neuroscience & Biobehavioral Reviews, 74, 287–296. https://doi.org/10.1016/j.neubiorev.2016.11.001
Cleare, A. J. (2004). The HPA axis and the genesis of chronic fatigue syndrome. Trends in Endocrinology & Metabolism, 15(2), 55–59. https://doi.org/10.1016/j.tem.2003.12.002
Institute of Medicine. (2015). Beyond myalgic encephalomyelitis/chronic fatigue syndrome: Redefining an illness. National Academies Press. https://doi.org/10.17226/19012
Jason, L. A., Sunnquist, M., & Brown, A. (2015). Chronic fatigue syndrome: Diagnostic criteria reconsidered. Journal of Clinical Psychology, 71(5), 466–479. https://doi.org/10.1002/jclp.22174
McEwen, B. S., & Akil, H. (2020). Revisiting the stress concept: Implications for affective disorders. Journal of Neuroscience, 40(1), 12–21. https://doi.org/10.1523/JNEUROSCI.0733-19.2019
Pace, T. W. W., & Heim, C. M. (2011). A short review on the psychoneuroimmunology of chronic fatigue syndrome. Brain, Behavior, and Immunity, 25(1), 7–13. https://doi.org/10.1016/j.bbi.2010.06.003
VanElzakker, M. B., Brumfield, S. A., & Lara Mejia, P. S. (2019). Neuroinflammation and cytokines in chronic fatigue syndrome. Frontiers in Psychiatry, 10, 102. https://doi.org/10.3389/fpsyt.2019.00102
Yehuda, R., & LeDoux, J. (2007). Response variation following trauma: A translational neuroscience approach to PTSD. Neuron, 56(1), 19–32. https://doi.org/10.1016/j.neuron.2007.09.006
Walker, M. P. (2017). Why we sleep: Unlocking the power of sleep and dreams. Scribner.