Gulf War syndrome

Gulf War syndrome, also called Gulf War illness or chronic multisymptom illness, is a persistent multi-organ condition affecting veterans of the 1990 to 1991 Persian Gulf War, with fatigue, pain, cognitive complaints and sleep disturbance that have now lasted for more than three decades.

It is now linked mainly to low-level exposure to organophosphate nerve agents and pesticides, is not explained by combat stress, and in October 2025 received a dedicated code in the United States clinical modification of ICD-10.

Terminology and classification

• The names in use are Gulf War syndrome, Gulf War illness, chronic multisymptom illness and Persian Gulf syndrome, and patient groups increasingly prefer Gulf War illness because it avoids the implication of a single syndrome.
• ICD-10-CM introduced code T75.830 with seventh characters A, D and S on 1 October 2025, and companion code Z77.31 records contact with or suspected exposure to the Gulf War theatre.
• The WHO version of ICD-10 has no specific code, ICD-11 mortality and morbidity statistics have no dedicated category, and the condition is therefore usually coded under general symptom or ill-defined categories outside the United States.
• Other identifiers are SNOMED CT 95877004, UMLS C0282550, MedGen 8439 and MONDO:0005907, and there is no OMIM or Orphanet entry because the disorder is not Mendelian.
• Two case definitions dominate research, the 1998 Centers for Disease Control definition and the 1999 Kansas definition, and they identify overlapping but not identical groups of veterans.
• Gulf War illness is classified separately from post-traumatic stress disorder, traumatic brain injury, chronic fatigue syndrome and fibromyalgia, although it overlaps symptomatically with all of them.

History

• Coalition forces deployed about 697,000 United States personnel and a smaller British contingent to the Gulf in 1990 and 1991, and veterans began reporting fatigue, pain and cognitive problems while the war was still in progress.
• Early United States investigations in 1993 and 1996 documented excess symptoms among deployed veterans but could not identify a single cause, and official reviews initially emphasised psychological explanations.
• The Centers for Disease Control and Prevention proposed a working case definition in 1998, and the Kansas definition followed in 1999, giving epidemiologists standard tools for comparing populations.
• The Research Advisory Committee on Gulf War Veterans' Illnesses concluded in its 2008 report that the illness is a real condition associated with neurotoxic exposures rather than with deployment stress alone.
• In 2014 the Department of Veterans Affairs and the Department of Defense issued a clinical practice guideline for chronic multisymptom illness, which was updated in 2021 with recommendations for cognitive behavioural therapy and mindfulness-based therapies.
• A 2022 case-control study found a gene-environment interaction between the paraoxonase-1 Q192R genotype and low-level nerve agent exposure, and in 2025 the United States introduced a dedicated billing code after decades of lobbying.^[1]

Epidemiology

• Approximately 250,000 of the 697,000 deployed United States veterans, or roughly one in three, report an enduring chronic multisymptom illness attributable to service in the Gulf.
• The Royal British Legion estimated that up to 33,000 British Gulf War veterans could be living with the illness, and around 1,300 had claimed a war pension for related conditions when the report was written.
• Prevalence in the Veterans Affairs Million Veteran Program Gulf War era cohort was about 30 percent among deployed veterans, consistent with earlier surveys and with the 1990s estimates.^[2]
• Longitudinal follow-up showed that from 1995 to 2005 the health of deployed combat veterans deteriorated relative to non-deployed veterans, with more new chronic diagnoses, functional impairment and hospitalisation.^[3]
• The illness affects men and women who served in all military roles, including those with no combat exposure, and it has been reported in naval, air force and support personnel.
• Studies of later conflicts have not shown the same pattern, and the syndrome remains most strongly associated with service in the 1990 to 1991 Gulf theatre.
• A 2026 review reported that 27 of the 35 coalition countries contributing troops have identified Gulf War illness among their veterans, showing that the condition is multinational rather than confined to United States personnel.
• A 2025 Federal Register notice extended presumptive service connection to veterans deployed to Afghanistan, Somalia, Djibouti, Egypt, Jordan, Lebanon, Syria and Uzbekistan, recognising similar chronic multisymptom illness after later deployments.

Pathophysiology

• The leading hypothesis is that acetylcholinesterase inhibition by organophosphate compounds produced sustained cholinergic overactivity and secondary neuronal injury in susceptible individuals.
• Low-level exposure to sarin and cyclosarin occurred when coalition forces destroyed Iraqi chemical weapons facilities, and exposure intensity was estimated from plume modelling and from contemporaneous environmental sampling.^[4]
• Paraoxonase-1 detoxifies organophosphates, and the Q192R polymorphism, particularly in combination with low exposure, was associated with a markedly increased risk of Gulf War illness in a large case-control study.^[1]
• Pyridostigmine bromide, issued as pretreatment against nerve agent attack, and organophosphate pesticides used by troops may have contributed through the same cholinergic mechanism.
• Other proposed mechanisms include neuroinflammation, mitochondrial dysfunction, oxidative stress, impaired detoxification, hypothalamic-pituitary-adrenal axis dysregulation and autonomic dysfunction.
• Depleted uranium, oil well fire smoke, anthrax vaccination and infectious exposures have been studied but show weaker or inconsistent associations than organophosphates.

Clinical features

• Fatigue is almost universal, and it is typically persistent rather than post-exertional only, with a substantial proportion of patients meeting criteria for myalgic encephalomyelitis or chronic fatigue syndrome.
• Musculoskeletal pain, joint stiffness, headaches and widespread tenderness occur frequently and overlap with fibromyalgia, while gastrointestinal symptoms overlap with irritable bowel syndrome.
• Cognitive complaints include poor concentration, memory lapses, word-finding difficulty and slowed processing, and they are often the most disabling feature for younger veterans.
• Sleep disturbance, unrefreshing sleep, night sweats and disturbed sleep architecture are common, and coexisting obstructive sleep apnoea can amplify fatigue and cognitive symptoms.
• Respiratory symptoms, skin rashes, diarrhoea, chemical sensitivity and mood or anxiety symptoms are frequently reported and contribute to functional impairment and reduced quality of life.
• Physical examination and routine laboratory tests are usually normal, and the absence of objective abnormalities has historically led to dismissive clinical attitudes and delayed care.

Diagnosis

• The Centers for Disease Control definition requires at least one symptom from two of three domains, namely fatigue, mood and cognition, and musculoskeletal pain, present for six months or more.
• The Kansas definition is stricter and requires symptoms in at least three of six domains, with moderate severity and exclusion of other diagnoses, and it is often used in treatment trials.
• Deployment history is essential, including dates, locations, duties, pesticide use, pyridostigmine receipt, chemical alarms and exposure to smoke from oil well fires.
• There is no diagnostic biomarker, and testing is directed at excluding anaemia, thyroid disease, diabetes, sleep apnoea, autoimmune disease, chronic infection and malignancy.
• Standardised questionnaires, sleep studies, mental health screening and pain assessment document severity and provide a baseline for symptom-based management.
• The differential diagnosis includes post-traumatic stress disorder, depression, traumatic brain injury, fibromyalgia, chronic fatigue syndrome, irritable bowel syndrome, multiple sclerosis and medication-related fatigue.

Management

• The 2014 and 2021 VA and DoD guidelines recommend a structured, symptom-based programme rather than a single disease-modifying therapy, with cognitive behavioural therapy and graded exercise supported by moderate-strength evidence.
• Mindfulness-based therapies, problem-solving treatment and mind-body approaches such as Tai Chi have shown improvements in pain interference, fatigue, depression, anxiety and quality of life in recent trials.^[5]
• Sleep disorders should be actively treated, including obstructive sleep apnoea with positive airway pressure, insomnia with cognitive behavioural therapy for insomnia and circadian measures.
• Pain is managed with non-opioid strategies such as physical therapy, topical agents, non-steroidal anti-inflammatory drugs and selected neuromodulators, and long-term opioids are discouraged.
• Investigational options include oleoylethanolamide, coenzyme Q10, low-dose naltrexone and mitochondrial supplements, but none has regulatory approval and evidence remains exploratory.^[6]
• Care should be coordinated across primary care, rehabilitation, mental health and specialty services, with attention to disability benefits, employment and family support.
• The Veterans Affairs disability system compensates medically unexplained chronic multisymptom illness lasting at least six months and rated at least 10 percent disabling, which affects access to care, income and rehabilitation services.
• Exercise should be introduced gradually and tailored to the patient's post-exertional response, because fixed graded-exercise programmes can worsen fatigue and pain in some veterans.

Research and controversies

• Whether Gulf War illness is a distinct disease or a cluster of overlapping syndromes remains debated, and critics argue that case definitions select heterogeneous populations.
• The PON1 finding supports a biological mechanism, but replication in independent cohorts and clarification of the exposure metric are still required before it can guide clinical practice.^[1]
• Trial evidence is limited by small samples, different case definitions and heterogeneous outcomes, and the 2020 systematic review found only twelve randomized trials, each testing a different intervention.
• Research funding through the Gulf War Illness Research Program has exceeded 200 million dollars since 2006, yet no disease-modifying drug has emerged.
• Recognition of the condition in ICD-10-CM is expected to improve coding, access to care and epidemiological surveillance, and researchers will need to validate the new code in real-world data.
• Mortality, cancer risk and long-term neurological outcomes remain uncertain, and studies of ageing Gulf War veterans are needed to determine whether the illness accelerates neurodegenerative disease.