title: Natural history of severe eosinophilia with uncertain aetiology and proposals on a practical approach to its management.
abstract: BACKGROUND
  Eosinophilia is commonly encountered during clinical practice. Some can be attributed to well-defined causes while others cannot. Optimal management of hypereosinophilia with unknown aetiology is uncertain as the natural history is not well described.
  
  
  METHODS
  We retrospectively studied patients with hypereosinophilia (>5 × 10(9)/L) and described the characteristics, natural history and treatment of those with eosinophilia of uncertain aetiology.
  
  
  RESULTS
  There were 141 patients with hypereosinophilia: 87 with well-defined causes, 54 with uncertain aetiology. The latter was managed as hypereosinophilic syndrome (HES) (n = 5), idiopathic hypereosinophilia (IH) (n = 11), presumptive helminthic infection (n = 11) and reactive eosinophilia (n = 5), while 22 were insufficiently investigated and did not have definite working diagnoses. Their median age and peak eosinophil count were 64 (22 to 94) years and 10.0 (5.2-33.9) × 10(9)/L respectively. Forty-six per cent had symptoms attributable to eosinophilia, with the HES and insufficiently investigated groups having the highest (100%) and lowest (27%) percentages respectively. HES and IH patients were most extensively investigated. All 14 HES or IH patients who received steroids responded. All presumptive helminthic infection patients received mebendazole: nine responded, and two had unassessable responses. For the remaining patients, seven received steroids and all responded; one received mebendazole but defaulted; 19 were not treated: 11 resolved spontaneously. No non-HES patients developed eosinophilia-related organ dysfunction. No mortality was caused by hypereosinophilia.
  
  
  CONCLUSIONS
  Patients with hypereosinophilia of uncertain aetiology can be empirically managed according to working diagnoses derived from history taking, examination and selective investigations. Most patients have benign short-term outcomes, but longer monitoring is required to assess long-term outcomes from untreated hypereosinophilia.
authors.affiliation: Department of Haematology, Singapore General Hospital, Singapore. ang.ai.leen@sgh.com.sg
authors.forename: A L
authors.initials: AL
authors.lastname: Ang
authors.forename: R X
authors.initials: RX
authors.lastname: Wong
authors.forename: Q Y
authors.initials: QY
authors.lastname: Zhuang
authors.forename: Y C
authors.initials: YC
authors.lastname: Linn
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D019468:Disease Management; D004802:Eosinophilia / Q000209:etiology* / Q000473:pathology* / Q000628:therapy; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D008297:Male; D008875:Middle Aged; D012189:Retrospective Studies; D012720:Severity of Illness Index; D035501:Uncertainty; D055815:Young Adult