Idiopathic acute eosinophilic pneumonia

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					Idiopathic acute eosinophilic pneumonia
Authors: Doctor François Philit1, Professor Jean-François Cordier
Creation Date: February 2002
Update: April 2004

Scientific Editor: Professor Jean-François Cordier
Service de Réanimation Médicale et d'Assistance Respiratoire, Hôpital de la Croix Rousse, 93 Grande
Rue de la Croix Rousse, 69004 Lyon Cedex 04, France.

Disease name and synonyms
Diagnosis criteria
Clinical presentation
Diagnostic methods
Differential diagnosis
Treatment and outcome

Idiopathic acute eosinophilic pneumonia (IAEP) is characterized by acute febrile respiratory failure
associated with diffuse radiographic infiltrates and eosinophilia in bronchoalveolar lavage fluid (BAL) in
the absence of infection. Patients, who are initially healthy and often young, present with severe
hypoxemia (partial pressure oxygen / fractional inspiratory oxygen, PaO2/FiO2 < 200 in most cases). BAL
allows diagnosis by showing eosinophilia (25-80%) without evidence of infection. IAEP may be mistaken
for acute respiratory distress syndrome if BAL differential cell count is not performed. The exact
prevalence of IAEP is unknown. It is a rare disorder with less than 100 cases reported so far and the
largest series including 15 patients only. Steroid treatment is recommended since IAEP can lead to life-
threatening respiratory failure. No relapse is observed after recovery.

eosinophilic pneumonia, bronchoalveolar lavage, respiratory failure, ARDS

Disease name and synonyms                                             Diagnosis criteria
Idiopathic acute eosinophilic pneumonia (IAEP)                        The criteria currently proposed for diagnosis are:
Acute eosinophilic pneumonia                                          1. acute onset: onset of any symptoms usually
                                                                      within 7 days before presentation;
Definition                                                            2. fever;
Idiopathic acute eosinophilic pneumonia (IAEP)                        3. bilateral infiltrates in chest films;
is an eosinophilic pneumonia of undetermined                          4. severe hypoxemia: PaO2 (partial pressure
etiology without systemic manifestations. It is                       oxygen) on room air < 60 mm Hg, and/or oxygen
characterized by acute respiratory failure, diffuse                   saturation on room air < 90 %, and/or A-a
bilateral lung infiltrates on chest X-ray, and                        (alveolo-arterial) gradient > 40;
pulmonary eosinophilia (1). IAEP has been                             5. lung eosinophilia: bronchoalveolar lavage
characterized as a distinct entity in 1989 (2).                       (BAL) differential cell count with > 25%
                                                                      eosinophils (or predominance of eosinophils in
                                                                      open lung biopsy);

Philit, F. and Cordier J.F. Idiopathic acute eosinophilic pneumonia. Orphanet encyclopedia, February 2002.                                                                       1
6. no history of hypersensitivity to drugs, no                        White blood cell count at presentation usually
history or laboratory evidence of infection, and                      shows        increased        leukocytosis       with
no other known cause of eosinophilic lung                             predominance of neutrophils. Eosinophils are
disease (3).                                                          higher than 0.5 Giga (109)/L in only 1 third of
                                                                      cases (3). However, eosinophilia greater than
Frequency                                                             0.5 G/L is present at least in 50% of patients
The exact prevalence of IAEP is unknown. It is a                      during disease course. Severe hypoxemia is
rare disorder with less than 100 cases reported                       currently present, since most of the patients
so far and the largest series including 22                            present with partial pressure oxygen/ fractional
patients only (3, 4). In June 1999, we conducted                      inspiratory oxygen, PaO2/FiO2 below 200 at
a multicentric retrospective study of IAEP: in                        admission (3, 5).
June 1999, 5300 specialists in intensive care                         Finally, the clinical presentation of IAEP much
and/or respiratory medicine in France, Belgium,                       resembles that of acute lung injury or adult
and Switzerland received a letter asking them to                      respiratory distress syndrome (ARDS) in many
report the cases of IAEP they had previously                          cases: rapid onset of acute respiratory failure
observed. Among the 34 answers, 22 cases                              requiring mechanical ventilation in up to 2 thirds
fitted with the above-mentioned diagnosis criteria                    of patients (3, 5), bilateral infiltrates, and severe
of IAEP (5).                                                          hypoxemia (10). However, the high percentage
                                                                      of eosinophils at BAL differential cell count is the
Etiology                                                              most relevant distinctive feature between IAEP
No well-defined cause was found in the reported                       and ALI/ARDS, and it could be added as
cases of IAEP. However, in some patients, IAEP                        exclusion criteria for the diagnosis of ALI and
developed after exposure to dust (1). IAEP has                        ARDS (5).
also been reported in patients who started
smoking less than 3 months before disease                             Diagnostic methods
onset (6, 7). In our experience 6 out 8 smokers                       BAL is the key to diagnosis of IAEP, showing
with IAEP were recent smokers (5). It is unlikely                     eosinophilic alveolitis (37 to 54 %) and increased
that smoking is the sole cause of IAEP, but                           neutrophils and lymphocytes (3, 5). BAL fluid
exposure to smoke or other environmental                              culture and staining for fungi or other infectious
agents may facilitate the onset of IAEP.                              agents are negative. When performed,
                                                                      transbronchial or open lung biopsy shows
Clinical presentation                                                 alveolar and interstitial infiltration by eosinophils,
IAEP onset is acute in individuals that are initially                 associated with interstitial edema (3). Organizing
healthy. In contrast with chronic eosinophilic                        diffuse alveolar damage may also be present (8).
pneumonia, patients are young, with an average                        Lung      biopsy    may       be      considered    in
age at presentation usually below 30 years                            immunocompromised patients developing IAEP,
(29±15 in our series). Males are predominantly                        especially when potential fungi exposure is
affected (3, 5). The duration of symptoms until                       present (3), but BAL eosinophilia obviates this
diagnosis of IAEP is usually less than 7 days (2                      procedure in most non-immunocompromised
to 3 days). However, IAEP cases have been                             patients.
reported in patients with symptoms which lasted
up to 1 month (5, 8).                                                 Differential diagnosis
All the patients initially present with fever and                     1. Chronic eosinophilic pneumonia (CEP)
dyspnea, and two thirds of them have cough and                        IAEP differs from CEP mainly by its acute onset
chest pain. Myalgia and abdominal pain may                            within a few days (average of 19 weeks in CEP),
also be noted, but in less than one third of                          the absence of asthma (about of half of the
patients (3). At physical examination, all patients                   patients in CEP), a higher proportion of smokers,
are tachypneic, and crackles are a predominant                        a male predominance, the onset of acute
finding at auscultation (1, 3).                                       respiratory failure and no relapse after
Chest X-ray shows bilateral infiltrates in all the                    pneumonia improves (11).
patients. Diffuse bilateral air-spaces opacities,
mixed air-space and interstitial opacities are the                    2. Eosinophilic pneumonia of determined
3 most current radiographic patterns (3, 9).                          origin
Bilateral small pleural effusion is common.                           IAEP can resemble fungal pneumonia
Computed tomography of the chest confirms that                        (especially     invasive     aspergillosis      or
bilateral air-space opacities are the most current                    Pneumocystis        carinii   pneumonia          in
imaging pattern, associated with bilateral pleural                    immunocompromised patients) or parasitic lung
effusion in most of the patients. The chest X-ray                     infection (Strongyloides stercoralis, filaria, and
returns to normal within 1 month (3).

Philit, F. and Cordier J.F. Idiopathic acute eosinophilic pneumonia. Orphanet encyclopedia, February 2002.                                                                           2
others). A large number of drugs can also cause                       of the literature. Medicine 1996; 75:334-342.
eosinophilic pneumonia (1, 3).                                        4. Allen JD, Davis WB. Eosinophilic lung
                                                                      diseases. Am J Respir Crit Care Med 1994;
3. Churg-Strauss syndrome                                             150:1423-1438.
This systemic vasculitis associated with adult-                       5. Philit F, Langevin B, Etienne B, et al. Acute
onset asthma differs from IAEP by the presence                        eosinophilic pneumonia. A study of 22 patients.
of peripheral blood eosinophilia and the                              Am J Respir Crit Care Med 2001; 163:A980.
involvement of non-pulmonary organs (1).                              6. Shintani H, Fujimura M, Ishiura Y, Noto M. A
                                                                      case of cigarette smoking-induced acute
Treatment and outcome                                                 eosinophilic pneumonia showing tolerance.
Steroid therapy has been used in most of the                          Chest 2000; 117:277-279.
reported cases of IAEP. However, it may be                            7. Nakajima M, Manabe T, Niki Y, Matsushima
initiated only when an infectious cause has been                      M. Cigarette smoke-induced acute eosinophilic
confidently excluded (3). The dose and duration                       pneumonia. Radiology 1998; 207:829-831.
of steroid treatment vary widely in the literature,                   8. Tazelaar HD, Linz LJ, Colby TV, Myers JL,
but all treated patients received intravenous                         Limper AH. Acute eosinophilic pneumonia:
steroid first, and orally thereafter. In our                          histopathologic findings in nine patients. Am J
experience and in the literature, some patients                       Respir Crit Care Med 1997; 155:296-302.
recovered spontaneously (5, 12). Although                             9. King MA, Pope-Harman AL, Allen JD,
efficacy of steroid therapy has not been                              Christoforidis GA, Christoforidis AJ. Acute
demonstrated, it is recommended in IAEP                               eosinophilic pneumonia: radiologic and clinical
patients with life-threatening hypoxemia.                             features. Radiology 1997; 203:715-719.
When mechanical ventilation is required, the                          10. Alp H, Daum RS, Abrahams C, Wylam ME.
patient's condition improves rapidly and weaning                      Acute eosinophilic pneumonia: a cause of
is possible within 1 week (3, 5). In our                              reversible, severe, noninfectious respiratory
experience non-invasive ventilation has also                          failure. J Pediatr 1998; 132:540-543.
been successfully used with favourable outcome                        11. Marchand E, Reynaud-Gaubert M, Lauque
within a few days (5).                                                D, Durieu J, Tonnel AB, Cordier JF, and the
Except one reported case of hypoxemia-related                         Groupe d'Etudes et de Recherche sur les
death, patients usually recover rapidly. This                         Maladies Orphelines Pulmonaires (GERM"O"P).
constant favorable outcome is another clinical                        Idiopathic chronic eosinophilic pneumonia. A
feature that distinguish IAEP from ALI/ARDS.                          clinical and follow-up study of 62 cases.
After recovery, no eosinophilia is found at BAL                       Medicine 1998; 77:299-312.
(1). In contrast with CEP, no relapse occurs after                    12. Hayakawa H, Sato A, Toyoshima M,
stopping steroid treatment.                                           Imokawa S, Taniguchi M. A clinical study of
                                                                      idiopathic eosinophilic pneumonia. Chest 1994;
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Acute eosinophilic pneumonia as a reversible
cause of noninfectious respiratory failure. N Engl
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3. Pope-Harman AL, Davis WB, Allen ED,
Christoforidis AJ, Allen JD. Acute eosinophilic
pneumonia. A summary of 15 cases and review

Philit, F. and Cordier J.F. Idiopathic acute eosinophilic pneumonia. Orphanet encyclopedia, February 2002.                                                                     3