Eosinophil Count

Toxocaral disease (visceral larva migrans) is a typical parasitic disease in which eosinophil counts (eosinophils >30% on differential) are usually elevated. Taylor et al¹ point out, however, that up to 27% of children with toxocariasis have normal eosinophil counts. Thus, normal eosinophil counts do not rule out toxocaral disease or other parasitic infestations. The cytokine interleukin 5 appears to induce eosinophilia in patients with certain parasitic diseases.²

An important although rare cause of increased eosinophils in the peripheral blood is the acute hypereosinophilic syndrome (HES). Reported mortalities ranged from 81% to 95% in one to three years. The HES syndrome includes high peripheral WBC count, circulating early eosinophilic forms without blast cells, mental confusion, delusions, near coma, and severe cardiac symptoms. Consistently associated with a poor prognosis are WBC count ≥90,000/mm³, blast forms in blood, heart failure, and severe CNS symptoms (confusion, organic psychosis and coma). This condition may not be a true leukemic myeloproliferative disease, although concepts of HES are controversial.

Infiltrative lung diseases, in which peripheral blood eosinophils may be increased, include eosinophilic pneumonia, Löffler syndrome (often related to Ascaris infestation), and tropical eosinophilia (usually related to filariasis).³

Eosinophilic gastroenteritis may occur with blood eosinophilia.⁴

Eosinophilia myalgia syndrome (EMS) characterized by an eosinophil count of 2000 cells/mm³ or more and severe often incapacitating myalgia is possibly associated with the use of L-tryptophan-containing products (LTCPs). Further definition of this syndrome, causal association between LTCPs and EMS, and modifying etiologic factors/cofactors has been recommended and is being pursued by CDC.^5,6 EMS is potentially fatal (Guillain-Barré like ascending polyneuropathy) with a clinical course resembling the toxic oil syndrome that was epidemic in Spain in 1981.⁷