Chronic Fatigue Syndrome
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Direct answer
Chronic fatigue syndrome, also called myalgic encephalomyelitis or systemic exertion intolerance disease, is diagnosed clinically after exclusion: at least six months of substantially activity-limiting fatigue not relieved by rest, with post-exertional malaise — a disproportionate worsening after previously trivial exertion — plus unrefreshing sleep and either cognitive impairment or orthostatic intolerance, per the 2015 Institute of Medicine criteria. There is no diagnostic test and no curative drug; management is energy management with pacing, individualised symptom treatment for pain and sleep, and a cautious, monitored return of activity that never exceeds the patient's envelope, since 2021 National Institute for Health and Care Excellence guidance withdrew graded exercise therapy as a default recommendation. In India the diagnosis is often delayed because the differential — anaemia, hypothyroidism, tuberculosis, depression, diabetes — must first be excluded and re-examined, and because post-viral fatigue clinics barely exist outside major centres.
What you must remember
- Core diagnostic triad: six months or more of medically unexplained, activity-limiting fatigue; post-exertional malaise; and unrefreshing sleep — with cognitive dysfunction ("brain fog") or orthostatic intolerance completing the criteria set.
- Exclusion screen before labelling: full blood count, erythrocyte sedimentation rate or C-reactive protein, thyroid-stimulating hormone, fasting glucose, electrolytes, creatinine, liver tests, human immunodeficiency virus and hepatitis serology where indicated, and a drug and alcohol history — the diagnosis is one of exclusion and follow-up.
- What it is not: fatigue explained by anaemia, hypothyroidism, sleep apnoea, depression, tuberculosis or malignancy — and the exam expects you to name the screen rather than accept the label at face value.
- Pacing over pushing: energy management keeps expenditure within limits, plans rest before crashes and avoids the boom-bust cycle; per the 2021 NICE guideline, graded exercise therapy is no longer offered routinely and cognitive behavioural therapy is supportive, not curative.
- Overlap territory: a substantial proportion report onset after viral infection — dengue, chikungunya, Epstein-Barr and notably post-coronavirus disease states share the post-exertional malaise phenotype, making the criteria newly relevant in Indian practice.
- Comorbidities to treat in their own right: fibromyalgia-type widespread pain, irritable bowel syndrome, orthostatic intolerance including postural orthostatic tachycardia syndrome, and depression or anxiety — each treated on its own evidence.
- Red flags redirecting the workup: weight loss, fever, lymphadenopathy, focal neurological signs, raised inflammatory markers — these are not chronic fatigue syndrome and reopen the search.
A typical clinic case
A 34-year-old teacher presents with ten months of exhaustion after a documented dengue infection; she sleeps twelve hours and wakes unrefreshed, and a supermarket trip confines her to bed for two days. The reasoning runs in three moves. First, exclude with the screen above plus a tilt-standing bedside test for orthostatic vitals — all normal, repeated once, Second, apply the criteria: duration well past six months, activity substantially reduced, unmistakable post-exertional malaise, unrefreshing sleep and concentration difficulty — the clinical box is ticked and she is told the diagnosis explicitly, because naming the illness reduces iatrogenic harm. Third, manage: pacing diary with her worst-day baseline, sleep hygiene without sedative dependence, low-dose symptomatic treatment for myalgia, a planned workplace accommodation letter, and scheduled review every few months to re-examine and catch any evolving alternative diagnosis. The case teaches the shape of good care — exclusion, explanation, envelope-based rehabilitation, vigilance — in a condition with no single decisive test.
Where students slip
Two errors dominate. The first is treating the label as a diagnosis of exclusion so aggressive that the patient is investigated for years and never told what they have — the criteria are clinical and positive once the screen is clean, and delayed naming is itself harmful. The second is reflexively prescribing graded exercise: the exam-aware answer reflects the 2021 NICE position that therapy must be individualised, malaise-monitored and never a fixed escalating protocol, because post-exertional worsening is the defining symptom. A third, quieter slip is conflating chronic fatigue syndrome with depression — the discrimination lies in anhedonia and mood change dominating depression, while effort-triggered physical deterioration and unrefreshing sleep dominate chronic fatigue syndrome, though they coexist often enough that both need treating.
Frequently asked questions
What are the Institute of Medicine criteria for chronic fatigue syndrome?
Six months of substantial activity-limiting fatigue with post-exertional malaise and unrefreshing sleep, plus cognitive impairment or orthostatic intolerance, after excluding alternatives.
Which investigations precede the diagnosis?
Full blood count, inflammatory markers, thyroid-stimulating hormone, glucose, renal and liver biochemistry, and where indicated human immunodeficiency virus and hepatitis serology — a defined exclusion screen.
What changed in the 2021 NICE guideline?
Graded exercise therapy was withdrawn as a routine recommendation; energy management with pacing, delivered individually and monitored for post-exertional worsening, became the core approach.
What is post-exertional malaise?
Disproportionate deterioration in symptoms — exhaustion, cognitive fog, myalgia — beginning hours to a day after exertion that the patient previously tolerated, lasting days.
How is chronic fatigue syndrome distinguished from depression?
Depression leads with anhedonia, guilt and mood change; chronic fatigue syndrome leads with effort-triggered physical deterioration and unrefreshing sleep — though comorbidity is common and both are treated.