Idiopathic hypereosinophilic syndrome

Page most recently updated 7 September 2026

This page focuses on the reported psychiatric associations, which may be the initial presenting manifestation, and on other clinical features that may assist the psychiatrist or primary care physician in identifying the underlying diagnosis, considered through the lenses of the diagnostic lenses framework.

Idiopathic hypereosinophilic syndrome is an immune-mediated hematologic disorder characterized by persistent hypereosinophilia with eosinophil-mediated injury to one or more organs, in the absence of an identifiable underlying cause.

It can present with psychiatric features such as cognitive impairment, behavioural change, mood symptoms, anxiety, confusion, hallucinations, and, rarely, psychosis, particularly when the central nervous system is involved.

Other characteristic features include: neurological manifestations such as encephalopathy, headache, seizures, cerebrovascular events, and peripheral neuropathy. Thromboembolic complications may also occur as a consequence of eosinophil-mediated vascular injury and thrombosis.

From a multisystemic lens perspective, clinical features in other body systems include (but are not limited to):

  • Cardiovascular: eosinophilic myocarditis, intracardiac thrombosis, endomyocardial fibrosis, valvular dysfunction, arrhythmias, and heart failure may occur and are important causes of morbidity.

  • Respiratory: cough, dyspnoea, pulmonary infiltrates, eosinophilic pulmonary inflammation, and, less commonly, pleural effusions may occur.

  • Gastrointestinal: abdominal pain, diarrhoea, nausea, and eosinophilic inflammation of the gastrointestinal tract may occur.

  • Hematologic: marked peripheral blood eosinophilia is defining, with anaemia, thrombocytopenia, or other hematologic abnormalities occurring in some patients.

  • Musculoskeletal: myalgias, arthralgias, and fatigue may occur.

  • Dermatologic: pruritus, urticaria, angioedema, and eczematous or pruritic papules and nodules are characteristic and among the most common manifestations.

Early diagnosis is important to identify and treat eosinophil-mediated organ injury before it becomes irreversible, particularly cardiac and neurological damage, guide appropriate eosinophil-lowering and immunomodulatory treatment, and reduce the risk of progressive multisystem organ dysfunction and mortality.

Selected references and further reading — Multisystemic lens

Cardinal RN, Bullmore ET. The diagnosis of psychosis. Cambridge: Cambridge University Press; 2011.

Sachdev PS, Keshavan MS, editors. Secondary schizophrenia. Cambridge: Cambridge University Press; 2010.

Levenson JL, editor. The American Psychiatric Association Publishing textbook of psychosomatic medicine and consultation-liaison psychiatry. 3rd ed. Washington (DC): American Psychiatric Association Publishing; 2019.

Stern TA, Beach SR, Smith FA, Freudenreich O, Vranceau AM, Fava M, editors. Massachusetts General Hospital handbook of general hospital psychiatry. 8th ed. Philadelphia: Elsevier; 2025.

Arciniegas DB, Yudofsky SC, Hales RE, editors. The American Psychiatric Association Publishing textbook of neuropsychiatry and clinical neurosciences. 6th ed. Washington (DC): American Psychiatric Association Publishing; 2018.

Agrawal N, Faruqui R, Bodani M, editors. Oxford textbook of neuropsychiatry. Oxford: Oxford University Press; 2020.

Boland R, Verduin M, editors. Kaplan and Sadock's comprehensive textbook of psychiatry. 11th ed. Philadelphia: Wolters Kluwer; 2024.

Loscalzo J, Fauci AS, Kasper DL, Hauser SL, Longo DL, Jameson JL, editors. Harrison's principles of internal medicine. 22nd ed. New York: McGraw Hill; 2025.