Chronic Fatigue Syndrome (ME/CFS)

Myalgic encephalomyelitis, also called chronic fatigue syndrome, is a serious, multi-system illness that has been misunderstood for decades and is still frequently misdiagnosed as depression or deconditioning. The Institute of Medicine criteria require three core features present for at least six months: substantial reduction in the ability to engage in pre-illness activity accompanied by fatigue, post-exertional malaise, and unrefreshing sleep — plus either cognitive impairment or orthostatic intolerance. Post-exertional malaise is the defining feature and separates ME/CFS from every other fatiguing condition. It is not simply tiredness after exertion. It is a delayed, disproportionate worsening of the whole symptom complex — fatigue, pain, cognitive dysfunction, flu-like malaise — typically appearing twelve to forty-eight hours after activity and lasting days or weeks. Crucially, the triggering activity can be trivial: a shower, a conversation, reading. This has direct treatment consequences. Two-day cardiopulmonary exercise testing demonstrates a reproducible abnormality in ME/CFS that does not occur in deconditioning: performance on the second day is worse than the first, indicating impaired recovery rather than lack of fitness. Graded exercise therapy, once standard, has been removed from major guidance including NICE after evidence of harm, and pacing — staying within an energy envelope — is the recommended approach. Onset frequently follows infection. Epstein-Barr virus, Ross River virus, Q fever, influenza and SARS-CoV-2 have all been documented triggers, and a substantial share of long COVID cases meet ME/CFS criteria. There is no diagnostic test and no approved treatment. Management is symptomatic: pacing, treating orthostatic intolerance, addressing sleep and pain, and avoiding the push-crash cycle.

• •Post-exertional malaise 12-48 hours after physical, cognitive or emotional exertion
• •Profound fatigue not relieved by rest, lasting over six months
• •Unrefreshing sleep despite adequate hours
• •Cognitive impairment — brain fog, slowed processing, word-finding difficulty
• •Orthostatic intolerance — dizziness or symptom worsening on standing
• •Widespread muscle and joint pain
• •Headaches of a new type or pattern
• •Sore throat and tender lymph nodes
• •Sensitivity to light, sound and certain foods

• •Post-viral onset — Epstein-Barr virus, enteroviruses, Ross River virus, Q fever, SARS-CoV-2
• •Immune dysregulation with altered cytokine profiles and natural killer cell dysfunction
• •Mitochondrial and bioenergetic impairment
• •Autonomic nervous system dysfunction, frequently with POTS
• •Hypothalamic-pituitary-adrenal axis abnormalities
• •Genetic susceptibility
• •Physical trauma or major surgery as a trigger in a minority

No single mechanism explains ME/CFS, and the most credible current model is a persistent dysregulated state triggered by an initial insult, usually infection, in a genetically susceptible person. Immune findings are among the most consistent: reduced natural killer cell cytotoxicity has been replicated repeatedly, and altered cytokine profiles have been reported, particularly early in illness. Whether these are causal or downstream remains unresolved. Bioenergetic abnormalities are also well documented. Studies show impaired ATP production in peripheral blood mononuclear cells, abnormal metabolomic signatures resembling a hypometabolic state, and the two-day cardiopulmonary exercise test abnormality — a reproducible failure to reproduce day-one performance on day two, which does not occur in sedentary controls or in depression. Autonomic dysfunction is common enough to be diagnostically useful. Postural orthostatic tachycardia syndrome coexists in a large minority, and cerebral blood flow reductions on standing have been demonstrated in ME/CFS patients even without meeting POTS criteria. Importantly, deconditioning does not explain the picture. Patients frequently develop the illness while highly active, and the day-two exercise test abnormality distinguishes ME/CFS from deconditioning directly.