Chronic Fatigue Syndrome (ME/CFS) — Causes, Symptoms, Diagnosis & Treatment Guide — Symptoms, Causes & Treatment | MyMedicPlus

Myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) is a serious, complex, long-term multisystem condition characterised by profound and disabling fatigue of more than 6 months duration that is not explained by any other condition, not relieved by rest, and significantly worsens with physical or mental exertion (post-exertional malaise — PEM). The IOM (Institute of Medicine, 2015) diagnostic criteria require all three core features: (1) substantial reduction in functioning with profound fatigue; (2) post-exertional malaise (PEM — characteristic worsening of all symptoms after any form of exertion, typically 12-48 hours later, lasting days or weeks); and (3) unrefreshing sleep — plus at least one of: cognitive impairment ('brain fog') or orthostatic intolerance. ME/CFS is a genuine biomedical condition — not a functional or psychosomatic disorder. Evidence demonstrates multiple abnormalities in immune activation, cellular energy metabolism (impaired mitochondrial function), autonomic dysregulation, and brain microglial activation. Long COVID shares pathophysiological mechanisms with ME/CFS and has substantially increased scientific attention and research funding for the condition.

The exact aetiology of ME/CFS remains incompletely understood but is multifactorial. Common precipitating triggers: viral infections (Epstein-Barr virus/glandular fever — 10% of infectious mononucleosis patients develop post-infectious fatigue; COVID-19 — estimated 10-15% of COVID-19 cases develop ME/CFS-like long COVID; enteroviruses), bacterial infections (Lyme disease, Q fever, Ross River virus), other immune system disruptions. Biological mechanisms under investigation: immune system dysregulation (elevated pro-inflammatory cytokines — IL-6, TNF-alpha, interferon-alpha; natural killer cell dysfunction; T-cell exhaustion markers); impaired mitochondrial energy metabolism (reduced ATP production — metabolomics studies showing characteristic patterns in PNAS by Naviaux et al.); autonomic nervous system dysfunction (small fibre neuropathy found in skin biopsies of some patients); orthostatic intolerance (delayed orthostatic hypotension or postural orthostatic tachycardia syndrome — POTS — present in many ME/CFS patients); HPA axis hypoactivation (blunted cortisol awakening response); brainstem neuroinflammation (neuroimaging studies); gut microbiome dysbiosis. Genetic predisposition (familial clustering observed). Risk factors: female sex, prior adversity reducing resilience, atopic conditions.

Core symptoms: Profound, disabling fatigue — not ordinary tiredness; significantly reduces ability to engage in pre-illness activities (work, school, social activities) by 50% or more; not relieved by rest. Post-exertional malaise (PEM) — the hallmark and diagnostic feature: worsening of all ME/CFS symptoms (fatigue, pain, cognitive function) typically 12-48 hours after physical, cognitive, social, or emotional exertion; often delayed in onset; can be triggered by minimal activity (a short walk, a shower, a conversation); can last days to weeks (a 'crash'). Unrefreshing sleep: sleep does not restore energy; often accompanied by sleep disorders (hypersomnia, insomnia, reversed circadian rhythm, disrupted sleep architecture on polysomnography). Cognitive impairment ('brain fog'): slowed processing speed, impaired short-term memory, word-finding difficulties, difficulty concentrating, inability to multitask. Orthostatic intolerance: dizziness, palpitations, and worsening symptoms on standing; pre-syncope; POTS (heart rate increase above 30 bpm on standing without orthostatic hypotension). Additional common symptoms: headaches, myalgia, arthralgia, sore throat and tender lymph nodes, sensory sensitivities (light, noise, smell), nausea and GI symptoms, temperature dysregulation. Severity ranges from mild (reduced functioning but able to perform some activities) to severe (housebound — 25% of ME/CFS patients) and very severe (bedbound, requiring assistance with all daily activities).

ME/CFS is a clinical diagnosis — no single diagnostic test exists. Diagnosis is based on meeting IOM 2015 or NICE 2021 criteria and excluding other conditions. NICE NG206 (2021): diagnosis requires all three of the following, present for at least 6 weeks in adults (3 weeks in children): (1) disabling fatigue not due to excessive exertion, not relieved by rest, significantly different from pre-illness; (2) post-exertional malaise; (3) unrefreshing sleep or sleep disturbance — plus one of: cognitive impairment or orthostatic intolerance. Diagnosis should not be delayed if symptoms are characteristic — NICE states diagnostic consideration at 4 weeks onset. Blood tests to exclude other conditions: FBC, CRP/ESR, LFTs, renal function, thyroid function (TSH), glucose/HbA1c, vitamin B12 and folate, vitamin D, coeliac antibodies, ferritin, CK, immunoglobulins, urinalysis — all typically normal in ME/CFS. Sleep study if sleep disorders or sleep apnoea suspected. NASA lean test or tilt table test for orthostatic intolerance/POTS. Exclude: depression (in depression motivation is often lost; in ME/CFS the will to be active is preserved but capacity is not), hypothyroidism, anaemia, sleep apnoea, inflammatory/autoimmune conditions, malignancy. ME/CFS and depression commonly coexist but are distinct conditions.

NICE 2021 guidance (NG206) represents a landmark change — it explicitly recommends AGAINST graded exercise therapy (GET) and cognitive behavioural therapy (CBT) as treatments intended to cure ME/CFS, or as first-line treatment, having concluded that the PACE trial evidence base was flawed and GET risks causing harm through triggering PEM crashes. Energy management (pacing — the cornerstone of current management): teaching patients to stay within their 'energy envelope' — the sustainable level of activity that does not trigger PEM; establishing a stable baseline before cautiously increasing activity (only if symptom-free for 2 weeks at current level — by 10% increments with minimum 6-week gaps); using heart rate monitoring (stay below anaerobic threshold — approximately 60% of maximum heart rate) to prevent PEM; includes physical, cognitive, social, and emotional activity. Sleep management: regular wake times; sleep hygiene; avoid prolonged daytime napping if worsening night sleep; melatonin for circadian rhythm disruption; low-dose tricyclics (amitriptyline 10-25 mg at night) for unrefreshing sleep and pain (off-label). Orthostatic intolerance/POTS: increased salt and fluid intake (2-3 litres/day with added salt); compression stockings; tilt training; low-dose beta-blockers or ivabradine (specialist-initiated) for refractory POTS. Pain: low-dose naltrexone (LDN — emerging evidence, off-label); pregabalin or gabapentin for neuropathic pain. Psychological support (to support coping with chronic illness, not as ME/CFS treatment): acceptance-based CBT, peer support groups, specialist ME/CFS clinics with multidisciplinary teams (physiotherapy, occupational therapy, dietetics).

ME/CFS causes a wide range of serious complications, particularly in severe and very severe cases. Severe disability and housebound or bedbound state: approximately 25% of ME/CFS patients are severely affected — housebound and unable to manage basic daily tasks; 1-2% are so severely ill that they are bedbound and require assistance for all activities of daily living. Post-exertional crashes: repeated triggering of PEM without adequate recovery leads to sustained deterioration and can result in permanent loss of function. Orthostatic intolerance complications: untreated POTS can cause recurrent syncope (fainting), fall-related injuries, and severe functional limitation. Nutritional deficiencies: inability to prepare meals, severe nausea, or gastrointestinal dysfunction leads to significant nutritional deficits — vitamin D, B12, and iron deficiency are common. Mental health deterioration: living with severe, disabling, and often medically dismissed illness causes depression, anxiety, grief, and social isolation — reported in 30-60% of patients. Secondary deconditioning: prolonged inactivity leads to muscle atrophy and cardiovascular deconditioning, further worsening functional capacity. Financial and occupational harm: ME/CFS forces 75% of sufferers to stop working or significantly reduce working hours, causing profound economic hardship.

Understanding and avoiding PEM is the most important self-management strategy. Keep a symptom and activity diary to identify triggers and personal activity limits. Use heart rate monitoring to stay below the anaerobic threshold during all activity. Plan carefully — distribute activities across the day, incorporate rest between tasks, and plan recovery time after any significant exertion. Avoid the 'push-crash' cycle (overdoing activity on 'good days' consistently leads to crashes lasting days to weeks — a key barrier to recovery). Rest at the first sign of symptom worsening — horizontal rest is more restorative than seated rest. Attend post-viral illness review early — prompt recognition and rest during acute viral illness may reduce the risk of post-infectious ME/CFS developing. Pacing education and ME/CFS peer support groups (ME Association, Action for ME in UK) significantly improve self-management. Optimise sleep, nutrition, and mental wellbeing. Long COVID patients developing ME/CFS symptoms should be referred to specialist ME/CFS or long COVID clinics promptly — early management education improves outcomes.

Consult your GP for persistent, disabling fatigue lasting more than 4 weeks (3-6 weeks in children) that is not explained by obvious causes and is worsened by physical or mental activity — NICE recommends diagnostic consideration at 4 weeks. Request referral to a specialist ME/CFS service for confirmed or suspected ME/CFS, diagnostic uncertainty, severe or rapidly worsening disability, suspected comorbidities (POTS, sleep disorders, chronic pain). Seek urgent medical review for: unexplained weight loss, night sweats, fever, lymphadenopathy, or focal neurological signs (to exclude malignancy, infection, or inflammatory disease mimicking ME/CFS); sudden severe deterioration without obvious precipitant. For very severe or bedbound patients, NICE recommends that home visits by specialist teams should be offered — attending clinic itself may cause significant post-exertional worsening. Consider NICE NG206 guidance when speaking to healthcare professionals — some clinicians may still recommend GET, which is now contraindicated per NICE.