Eosinophilic Pneumonia of Undetermined Origin

Prior asthma may antedate the diagnosis of ICEP, occur concomitantly, or develop in subsequent years (8). Overall, it is present in approximately two thirds of patients, and may get worse after the occurrence of ICEP, requiring prolonged 

Peripheral blood eosinophiha is almost always present in ICEP when blood count is performed prior to corticosteroid treatment (systemic corticosteroids may decrease dramatically the eosinophil cell count within 24—48 horn s), with a mean blood eosinophilia over 5 x 10 eosinophils/L in most series. Alveolar eosinophilia usually greater than 40% at BAL differential cell count is a hallmark of ICEP (9,60), with a mean of about 60% at differential cell count (9), and is key to the diagnosis. Total blood IgE level is increased in about half the cases. C-reactive protein is elevated. Urine excretion of the EDN/eosinophil protein X (EPX) is markedly increased, indicating active eosinophil degranulation (61). 

Lung function tests in ICEP show an obstructive ventilatory defect in about half the cases and a restrictive ventilatory defect in the other half (6,9). Usually mild hypoxemia is present in two thirds of patients. 

Although spontaneous resolution of ICEP may occasionally occur, treatment with oral corticosteroids is needed and is followed by dramatic clinical improvement and normalization of blood eosinophil level within 48 hours in about 80% of the patients (9). An initial dose of 0.5 mg/kg/day may be used for two weeks, followed by 0.25 mg/kg/day for two weeks, with further tapering of corticosteroids. Chest CT evenmally returns to normal in almost all patients, but streaky or bandlike opacities may persist in a minority of patients. Pulmonary opacities rapidly decrease in both size and extent, with possible evolution from consolidation to ground glass opacities or inhomogeneous opacities, and clear within one week. Similarly, the spirometry remms to normal with treatment in most patients, although persistent airflow obstruction may develop in isolated cases (9,62). 

Relapse occurs in over half of the patients afta- stopping the corticosteroid treatment or under a low daily dose of prednisone ( 10 mg/day) (6,9). Consequently, most patients require prolonged treatment for more than six months, and often several years. However, relapses respond very well to resumed corticosteoid treatment. Whether inhaled corticosteroids might reduce the rate of relapses of ICEP after stopping maintenance oral corticosteroids has not been demonstrated (8,9). 

---

The eosinophilic lung diseases and syndromes are characterized by prominent infiltration of the lung by polymorphonuclear eosinophils, often associated with marked peripheral blood eosinophilia and eosinophilia at bronchoalveolar lavage (BAL), and may include parenchymal lung diseases as well as diseases of the lower airways (1). The diseases associated with eosinophilic pneumonia developed in this chapter may be separated into eosinophilic pneumonia of undetermined origin and well-individualized syndromes, and eosinophilic pneumonia with a definite cause (mainly infection and drug reaction) (Table 1). 

---