Chronic fatigue syndrome — diagnostic criteria, clinical manifestations, predisposing factors, course, prognosis and treatment

Definition. Chronic fatigue syndrome, also called myalgic encephalomyelitis (ME/CFS) and, in the IOM formulation, systemic exertion intolerance disease, is a chronic, disabling, multisystem illness characterised by profound fatigue that is not explained by ongoing exertion, is not relieved by rest, and causes a substantial reduction in previous levels of occupational, social and personal activity, together with post-exertional malaise and unrefreshing sleep, persisting for at least six months (or, under NICE, three months for diagnosis) and not attributable to another disorder.

Diagnostic criteria — IOM / National Academy of Medicine 2015. Diagnosis requires all three of: (i) a substantial reduction or impairment in the ability to engage in pre-illness levels of activity, persisting more than six months, accompanied by fatigue that is often profound, of new or definite onset, not the result of ongoing excessive exertion, and not substantially alleviated by rest; (ii) post-exertional malaise; and (iii) unrefreshing sleep. Plus at least one of: cognitive impairment or orthostatic intolerance. Symptoms should be present for at least half the time and of at least moderate intensity.

Diagnostic criteria — Fukuda (CDC) 1994, still widely quoted in examinations. Clinically evaluated, unexplained, persistent or relapsing fatigue for six months or more, of new onset, not the result of ongoing exertion, not substantially alleviated by rest, and resulting in substantial reduction in previous activity levels — plus four or more of the following eight, concurrently present for six months: impaired short-term memory or concentration; sore throat; tender cervical or axillary lymph nodes; muscle pain; multi-joint pain without swelling or redness; headaches of a new type, pattern or severity; unrefreshing sleep; and post-exertional malaise lasting more than 24 hours.

Post-exertional malaise is the cardinal feature — and the examinable one. PEM is a disproportionate worsening of symptoms after physical, cognitive, emotional or social exertion that was previously tolerated, characteristically delayed in onset by hours to days and disproportionately prolonged, taking days, weeks or longer to recover. It is not ordinary post-exertional fatigue, and this distinction determines the entire management approach. NICE NG206 makes post-exertional malaise mandatory for the diagnosis.

Clinical manifestations. Constitutional — profound fatigue, PEM, unrefreshing sleep, sleep-phase disturbance. Neurocognitive — "brain fog", impaired concentration, word-finding and short-term memory difficulty, slowed information processing, sensory hypersensitivity to light and noise. Autonomic — orthostatic intolerance, postural orthostatic tachycardia, palpitations, dizziness, nausea, temperature dysregulation. Musculoskeletal — widespread myalgia, arthralgia without swelling, muscle weakness. Immune-like — recurrent sore throat, tender lymph nodes, flu-like malaise. Gastrointestinal — irritable bowel symptoms. Severity spans from those who continue reduced work to the severely affected, who are housebound or bedbound and require assistance with all activities of daily living — a group of about 25%.

Predisposing, precipitating and perpetuating factors. Predisposing — female sex (2–4:1), genetic susceptibility, pre-existing anxiety or depression, childhood adversity, and a personality pattern of high achievement and persistence. Precipitating — most characteristically an infection: Epstein–Barr virus, Q fever, Ross River virus, enterovirus, influenza, and now SARS-CoV-2; also major physical trauma, surgery, or severe psychological stress. Perpetuating — the boom-and-bust cycle of over-activity followed by collapse, deconditioning, disturbed sleep, chronic pain, comorbid mood disorder, and iatrogenic harm from inappropriate exercise prescription. Proposed mechanisms — none diagnostic — include immune dysregulation with altered cytokine profiles, hypothalamic–pituitary–adrenal axis hypofunction, autonomic dysfunction, and impaired cellular energy metabolism. This last is directly supported in the geriatric literature: idiopathic chronic fatigue in older adults has been linked to impaired mitochondrial content and biogenesis signalling in skeletal muscle.

Diagnosis is clinical — investigations are to exclude, not to confirm. There is no diagnostic test. A baseline screen excludes the treatable mimics: full blood count, ESR and CRP, urea and electrolytes, creatinine, liver function, calcium, glucose and HbA1c, TSH, creatine kinase, ferritin, vitamin B12 and folate, vitamin D, coeliac serology, urinalysis, and, where indicated, HIV, hepatitis serology, chest radiograph, ANA and cortisol. NICE recommends baseline investigation to exclude alternative diagnoses and regular follow-up investigation to capture new or missed diagnoses. The differential in an older adult is wide and matters more than in the young: anaemia, hypothyroidism, diabetes, occult malignancy, heart failure, chronic kidney disease, COPD, obstructive sleep apnoea, polymyalgia rheumatica, depression, sarcopenia and frailty, undernutrition, and — above all — drug adverse effects from beta blockers, opioids, antihistamines, benzodiazepines, antidepressants, statins and antihypertensives.

The particular problem in older adults. ME/CFS characteristically begins between 20 and 50 and a new diagnosis after 65 should be made only with great caution, because in that age group fatigue is far more likely to be the presenting feature of occult disease, polypharmacy, depression or frailty. In geriatric practice fatigue is therefore treated as a syndrome requiring evaluation, not a diagnosis. Where CFS/ME is genuinely present in an older person, it is usually long-standing disease carried into later life, in which case the clinical task is managing the interaction of ME/CFS with accumulating comorbidity, deconditioning, sarcopenia and falls risk. In the related and better-studied model of cancer-related fatigue, the textbook approach is instructive: it is a multicomponent disturbance of neuroendocrine regulation and cytokine signalling, and management begins with a review of associated symptoms — pain, insomnia, depression — and a complete evaluation of possible medication side effects, since fatigue-inducing drugs are so often the cause.

Course and prognosis. The course is fluctuating, with relapses and remissions, typically punctuated by PEM-driven "crashes". Onset may be abrupt and post-infectious or insidious. Prognosis is generally poor for full recovery in adults: full recovery occurs in roughly 5–10%, some degree of improvement in about 40%, and the remainder run a chronic, fluctuating course; children and adolescents do considerably better. Favourable prognostic factors: shorter duration before diagnosis, milder illness, absence of comorbid psychiatric disorder, a clear infective trigger, younger age, and good social and family support. Adverse factors: long duration, severe or bedbound disease, older age, comorbid depression or anxiety, chronic pain, ongoing pursuit of a purely psychological explanation, and — importantly — iatrogenic deterioration from enforced exercise. Mortality is not directly increased, but there is excess suicide risk in the severely affected, and profound impairment of quality of life.

Treatment — there is no cure; management is supportive, individualised and multidisciplinary. (a) Energy management ("pacing") is the cornerstone: the patient establishes an individual "energy envelope" and stays within it, planning and prioritising activity and building in rest, rather than pushing through symptoms. (b) Sleep management — sleep hygiene, treatment of a reversed sleep-wake cycle, and screening for obstructive sleep apnoea, without hypnotics where possible. (c) Symptom-directed treatment — analgesia for pain following the analgesic ladder with attention to constipation and delirium risk in the old; low-dose amitriptyline or duloxetine for pain and sleep; increased fluid and salt, compression garments, and slow positional change for orthostatic intolerance, with fludrocortisone or midodrine reserved for specialist use; management of irritable bowel symptoms; and treatment of coexisting depression or anxiety, which is a comorbidity to be treated in its own right and not an explanation of the illness. (d) Psychological support — cognitive behavioural therapy may be offered as an adjunct to support coping and reduce the distress of chronic illness, but it is not a cure and must not be offered as one. (e) Rehabilitation and social care — physiotherapy aimed at maintaining, not increasing, function; occupational therapy, aids, adaptations, home care, disability certification and carer support. (f) Ruthless deprescribing of fatigue-inducing drugs, and correction of anaemia, thyroid disease and nutritional deficiency. In the specific setting of cancer-related fatigue, where a pharmacological trial is contemplated, methylphenidate is the best-studied agent and the usual first choice, with close monitoring, although trials show a marked placebo response and benefit largely confined to those with severe fatigue.

NICE NG206 reversed the previous standard of care, and the reversal has held. The changes are the most examinable content in this topic. Post-exertional malaise is now recognised as a core symptom and must be present for the diagnosis. ME/CFS can be confirmed after 3 months of symptoms rather than 4–6, balanced by baseline investigations to exclude alternative diagnoses and regular follow-up investigation to capture new or missed diagnoses. Graded exercise therapy is no longer recommended and should not be offered as a treatment for ME/CFS; people with ME/CFS should aim to remain within their energy limit and should not push through symptoms to complete tasks. Cognitive behavioural therapy is no longer considered a treatment for ME/CFS itself and should be used only as an adjunct — the guideline states explicitly that CBT "is not a cure for ME/CFS and should not be offered as such", but aims to improve wellbeing and quality of life and to reduce the distress of living with a chronic illness. Individualised care should be provided by a multidisciplinary team. The evidence base for graded exercise has continued to be criticised through 2025 for reliance on subjective self-report, poor recording of adverse effects, and biological data showing distinct immune and metabolic abnormalities in patients with PEM, which suggest that exercise may worsen symptoms.

Long COVID has transformed the epidemiology and the research landscape. A substantial proportion of people with long COVID meet ME/CFS criteria, so prevalence has risen sharply and the two conditions now share diagnostic and management pathways — pacing and energy management have been adopted in long-COVID rehabilitation precisely because of the ME/CFS experience with graded exercise. Two caveats to state for balance. First, NICE itself notes that NG206 should not be assumed to apply to post-COVID-19 syndrome, since its evidence was reviewed before the pandemic. Second, the relationship is not identical: in a comparative study, self-reported PEM was common in long COVID (67% of one questionnaire cohort), but objectively observed PEM after standardised cardiopulmonary exercise testing was infrequent, and when present was less severe and less prolonged than in ME/CFS. The practical geriatric implication is that older adults with post-COVID fatigue should be assessed for PEM specifically, since its presence dictates a pacing-based rather than a reconditioning-based rehabilitation plan — and getting this wrong causes harm.

The ageing kidney and the ageing endocrine system explain most of this syllabus. Blunted thirst, impaired urinary concentration and dilution, salt and urea wasting, hypoaldosteronism, poor acid handling, reduced receptor and post-receptor responsiveness. Open almost any answer with one line of that physiology and the clinical features follow logically.

Atypical presentation is the geriatric signature. Hypoglycaemia, HHS, hyponatraemia, hypercalcaemia, hypokalaemia, osteomalacia, pseudogout, thyrotoxicosis and heat stroke all present as falls, delirium, immobility or "just ageing" rather than as textbook syndromes. Say this once in every answer.

Creatinine lies, and so does HbA1c. Sarcopenia plus net tubular reabsorption means a normal creatinine can conceal a halved GFR; anaemia, CKD and transfusion make HbA1c falsely low. Dose every drug to the estimated GFR, and use glucose profiles or CGM where HbA1c is unreliable.

Deprescribing is treatment, not the absence of it. The thiazide in hyponatraemia and gout, the NSAID or PPI in interstitial nephritis and hypomagnesaemia, the SSRI in SIADH, the salt substitute in hyperkalaemia, the sulphonylurea in hypoglycaemia, the unnecessary levothyroxine — successfully withdrawn from half of the nursing-home residents studied.

Start low, go slow, and accept an imperfect target. Levothyroxine 12.5–25 µg, allopurinol under 100 mg, acarbose 25 mg, HbA1c 7–8%, TSH 6–7, sodium correction ≤8–10 mEq per 24 hours. The old are harmed by aggressive normalisation, and correction speed punishes more often than the number itself.

Function and frailty, not chronological age, drive every decision — renal biopsy, immunosuppression, dialysis modality, transplantation, thyroid surgery, testosterone therapy and glycaemic targets alike. Age is never, on its own, a contraindication. INDIAN CONTEXT — READY-TO-USE LINES FOR ANY ANSWER Programme / framework What to write NPHCE National Programme for the Health Care of the Elderly — geriatric clinics, Regional Geriatric Centres, district geriatric units NPCDCS Opportunistic screening for diabetes and hypertension at health and wellness centres; the entry point for early CKD and diabetic foot detection PMNDP Pradhan Mantri National Dialysis Programme — free district-level haemodialysis in PPP mode, with policy expansion of peritoneal dialysis AB-PMJAY / Ayushman Vay Dialysis and hospital packages; the Vay Vandana Card covers all citizens aged 70 and Vandana Card above irrespective of income NDMA Heat Action Plans · Ahmedabad HAP as the national model; NCDC "Emergency Cooling for Severe Heat-NCDC/NPCCHH Related Illnesses" (March 2024), including improvised immersion using a body bag or tarpaulin; ambulance 108 ICMR-NIN Dietary reference values, calcium and vitamin D intake, and food-fortification policy — the pragmatic alternative to population-wide 25(OH)D testing ADIP–ALIMCO · Rashtriya Assistive devices including therapeutic footwear for the diabetic foot Vayoshri Yojana Disease-specific Indian points CKD of unknown aetiology (CKDu) in the agricultural belts of Andhra Pradesh, Odisha and Tamil Nadu · tuberculosis as a granulomatous cause of hypercalcaemia and a pulmonary cause of SIADH · iodine-deficient regions making toxic nodular goitre relatively commoner than Graves' disease · potassium-containing "low-sodium salt" and aristolochic acid in herbal preparations · barefoot walking as a diabetic-foot risk · high-carbohydrate diets justifying voglibose and acarbose · cheap generic empagliflozin and dapagliflozin against costly GLP-1 receptor agonists · HLA-B*5801 in about 7% of those of Southeast Asian descent · Kerala's community palliative care network as the model for conservative kidney management