E3 PreliminaryPreliminaryPEM not requiredReview-NarrativePeer-reviewedReviewed
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The HPA axis and the genesis of chronic fatigue syndrome.
Cleare, Anthony J · Trends in endocrinology and metabolism: TEM · 2004 · DOI
Quick Summary
This review examines whether ME/CFS involves problems with the body's stress hormone system (the HPA axis). While people with long-standing ME/CFS show some changes in this system, early studies suggest these changes may not be present when the illness first develops. Interestingly, lifestyle factors like inactivity and poor sleep may cause these changes, and they can sometimes improve when these factors are addressed.
Why It Matters
Understanding whether HPA axis changes cause ME/CFS or result from it has major implications for treatment strategies. If these changes are consequences rather than causes, interventions targeting the HPA axis alone may be insufficient, but addressing behavior and lifestyle might help. This challenges assumptions about the fundamental biology of ME/CFS and redirects research focus toward prevention and early intervention.
Observed Findings
Long-standing CFS patients show mild hypocortisolism, heightened negative feedback, and blunted HPA responses to challenge.
Prospective studies of early fatiguing illness do not show HPA axis abnormalities at disease onset.
Behavioral modifications (increasing activity, improving sleep, reducing deconditioning) can reverse some observed HPA changes.
Pharmacological cortisol elevation temporarily reduces fatigue symptoms in some patients.
HPA alterations appear multifactorial in origin rather than specific to CFS.
Inferred Conclusions
HPA axis changes in CFS are likely consequences of prolonged illness and associated lifestyle factors rather than primary pathogenic mechanisms.
No specific, pathognomonic HPA axis abnormality defines CFS, distinguishing it from other conditions.
The HPA axis may play a secondary role in perpetuating symptoms once illness is established, even if not causative at inception.
Behavioral and lifestyle interventions may be more effective than hormonal replacement in addressing HPA-related symptom contributions.
Remaining Questions
Do HPA axis changes emerge gradually during the transition from early to chronic illness, and what factors trigger this transition?
What This Study Does Not Prove
This study does not prove that the HPA axis plays no role in ME/CFS pathogenesis—only that it may not be a primary causative factor. The review cannot establish definitive causal relationships between lifestyle factors and HPA changes, as it synthesizes existing literature rather than presenting new experimental data. It also does not address whether HPA dysfunction might be important in specific subgroups of ME/CFS patients.
About the PEM badge: “PEM required” means post-exertional malaise was an explicit required diagnostic criterion for participant inclusion in this study — not that PEM was studied, observed, or discussed. Studies using criteria that do not require PEM (e.g. Fukuda, Oxford) are tagged “PEM not required”. How the atlas works →
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