Landmark Review Maps the Biology and Broken History of Chronic Fatigue Syndrome

Myalgic encephalomyelitis, more commonly known as chronic fatigue syndrome, has long occupied an uncomfortable position in medicine: a disease that leaves millions of patients profoundly disabled, yet one that has been repeatedly dismissed, misdiagnosed, and starved of research funding. A comprehensive review published in the Journal of Translational Medicine by Madhan Jeyaraman, Filippo Migliorini, and colleagues now assembles the scattered evidence on ME/CFS into a single, sobering portrait. The authors argue that the condition is neither psychological in origin nor a vague collection of complaints, but a multisystem illness with measurable disturbances in energy metabolism, immune signaling, autonomic regulation, and the gut microbiome. Their synthesis arrives at a moment of unusual opportunity, as the overlap between ME/CFS and Long COVID has pushed post-infectious chronic illness from the margins of medicine into the center of scientific attention.

The clinical picture the review describes is dominated by a symptom that has no equivalent in most other diseases: post-exertional malaise, or PEM. Patients with ME/CFS experience a worsening of fatigue, pain, cognitive dysfunction, and other symptoms after physical or mental exertion, and the deterioration is disproportionate and delayed, often appearing a day or more after the triggering activity. The authors identify PEM as the cardinal feature of the disease, the hallmark that most reliably distinguishes it from ordinary fatigue or depression. Alongside PEM, the core clinical characteristics include persistent, unexplained fatigue that does not resolve with rest, unrefreshing sleep, and cognitive impairment that patients frequently describe as brain fog. Multisystem involvement means that cardiovascular, gastrointestinal, neurological, and immunological symptoms can all coexist in the same patient, making the presentation bewilderingly heterogeneous.

That heterogeneity has been one of the greatest obstacles to scientific progress. The review traces the history of diagnostic criteria for ME/CFS and finds a succession of definitions that varied widely in their requirements, producing patient populations that were not comparable across studies. Some earlier criteria emphasized fatigue alone, a choice that allowed conditions such as major depressive disorder to be folded into the diagnosis and reinforced the historical linkage of ME/CFS to psychiatry. The authors are blunt about the consequences: inconsistent diagnostics, the absence of any validated biomarker, and decades of psychological framing delayed recognition of the disease and marginalized the patients living with it. Diagnosis today remains clinical, resting on symptom patterns and the exclusion of other conditions, which means that underdiagnosis is widespread and prevalence estimates vary considerably across countries and study designs.

One of the most consequential shifts documented in the review concerns treatment. For years, graded exercise therapy was offered to ME/CFS patients on the theory that deconditioning perpetuated their symptoms and that carefully escalated activity would restore function. The review notes that this approach has now been formally withdrawn from treatment guidelines, with evidence of harm: for a disease in which exertion itself triggers pathological worsening, pushing patients to exercise can precipitate severe and prolonged relapses. The withdrawal represents an acknowledgment that a treatment paradigm built on the wrong model of the disease caused real damage. Pacing, the strategy of carefully balancing activity and rest to stay within an individual’s energy envelope, remains a pragmatic management approach, but the review is clear that no disease-modifying treatment currently exists.

The pathophysiological section of the review is where the technical story becomes most compelling. Multiple independent lines of evidence now point to mitochondrial dysfunction as a central abnormality. Mitochondria are the cellular power plants that convert nutrients into adenosine triphosphate, the molecular currency of energy, and studies in ME/CFS patients have found impaired energy production and abnormal metabolic profiles consistent with cells that cannot generate ATP efficiently. Metabolomic assays, which survey hundreds of small molecules in blood or urine, have detected reproducible disturbances in energy metabolism pathways, and some researchers have proposed these metabolic signatures as candidate diagnostic biomarkers. Electrophysiological assays, which measure the electrical activity of cells, offer another emerging tool for objectifying a disease that has long lacked laboratory confirmation.

Immune dysregulation forms a second pillar of the pathophysiological evidence. The review describes abnormalities in immune cell function and inflammatory signaling that suggest the immune system in ME/CFS is chronically activated yet ineffective, a state that could explain both the flu-like symptoms many patients report and their vulnerability to symptom flares. Autonomic imbalance is a third strand: dysregulation of the autonomic nervous system, which controls heart rate, blood pressure, and other involuntary functions, manifests as orthostatic intolerance and other cardiovascular symptoms that worsen when patients stand upright. Neuroinflammation, inflammation within the central nervous system, provides a plausible mechanism for the cognitive impairment that so many patients experience. Finally, alterations in the gut microbiome, the community of microorganisms inhabiting the intestine, have been documented in ME/CFS and may contribute to systemic inflammation through the gut-immune axis.

On the therapeutic frontier, the review highlights several strategies under investigation. Among the most intriguing are mTOR inhibitors, drugs that modulate the mechanistic target of rapamycin pathway, a central cellular signaling hub that regulates metabolism, growth, and autophagy. Given the metabolic disturbances observed in patients, pathway modulation represents a rational therapeutic hypothesis, though the authors present it as exploratory rather than established. The review also emphasizes methodological innovation: decentralised clinical trial designs, which recruit and follow participants remotely rather than requiring frequent visits to academic centers, could overcome one of the practical barriers that has hampered ME/CFS research, namely that the disease itself often prevents patients from traveling to study sites.

The intersection with Long COVID receives particular emphasis as a scientific accelerant. A substantial fraction of people infected with SARS-CoV-2 develop a chronic post-infectious syndrome whose symptoms overlap strikingly with ME/CFS, including PEM, cognitive dysfunction, and unrefreshing sleep. The review frames this convergence as a chance to rapidly advance the study of post-infectious chronic diseases more broadly, because Long COVID has attracted funding, patient cohorts, and scientific talent on a scale ME/CFS never achieved. Insights from one condition are likely to inform the other, and the enlarged research community now working on post-acute infection syndromes may finally supply the mechanistic answers that decades of ME/CFS research struggled to reach in isolation.

To convert this momentum into durable progress, the authors argue for stringent subtyping of patients, uniform data collection across studies, and ongoing patient participation in research design. Subtyping acknowledges that ME/CFS may encompass several distinct biological subgroups with different triggers and mechanisms, and that pooling them has obscured signals in past studies. Standardized data collection would make findings comparable across laboratories and countries, while involving patients, who possess detailed experiential knowledge of symptom patterns and treatment harms, would help ensure that research questions and outcome measures are clinically meaningful. The review closes with a call for equitable research funding, contending that biomarker discovery and the development of disease-modifying treatments will remain out of reach until investment matches the disease burden. Caring for people with ME/CFS, the authors conclude, is not only a clinical obligation but a public health one, a statement that would have been difficult to publish in a major translational medicine journal a generation ago.

Subject of Research: Pathophysiology, diagnosis, and treatment of myalgic encephalomyelitis/chronic fatigue syndrome

Article Title: Comprehensive review of myalgic encephalomyelitis/chronic fatigue syndrome

Article References: Jeyaraman, M., Jeyaraman, N., Ramasubramanian, S., Schäfer, L., Migliorini, F., & Balaji, S. (2026). Comprehensive review of myalgic encephalomyelitis/chronic fatigue syndrome. Journal of Translational Medicine. https://doi.org/10.1186/s12967-026-08833-4

Image Credits: AI Generated

DOI: 10.1186/s12967-026-08833-4

Keywords: ME/CFS, chronic fatigue syndrome, post-exertional malaise, mitochondrial dysfunction, neuroinflammation, immune dysregulation, autonomic dysfunction, gut microbiome, Long COVID, graded exercise therapy, diagnostic criteria, biomarkers