1. 首先在1989年，於acute resp. failure的case中被描述。
2. AEP與CEP不同，雖然都是肺實質有eosinophilic infiltration
ETIOLOGY — cause unknown, 可能是對unidentified inhaled antigen有 acute hypersensitivity reaction。新抽菸者要考慮之。
PATHOLOGY — (資料不多，參考Mayo clinic的study)
1. Severe extent of disease (肺表面有75%以上的不正常)
2. 常見DAD (Acute and organizing diffuse alveolar damage); 會有 Hyaline membranes & interstitial widening (由於edema, fibroblast proliferation, 與inflammatory cells，以上這些是DAD 在organizing phase的表現)。
3. Marked numbers of interstitial and lesser numbers of alveolar eosinophils were found in all samples?? (不懂)
4. 其他可能的表現有: type II pneumocyte hyperplasia (55%), interstitial lymphocytes (100%), organizing intraalveolar fibrinous exudate (100%), perivascular and intramural inflammation without necrosis (33%)
5. 沒有Granulomas或alveolar hemorrhage。
CLINICAL FEATURES — 會出現於any age,甚至是healthy children。大部份病人約在20~40歲之間。男性居多， 是女性兩倍。少部份有過敏疾病。
1. Clinical presentation:
(1) acute illness(小於四週)；大部份症狀少於七天。症狀包括：乾咳(95%), 喘(92%),與發燒(88%)，另外也會有malaise, myalgias, night sweats, chills, and pleuritic chest pain。
(2) Physical examination: fever (often high), tachypnea, bibasilar inspiratory crackles, occasionally rhonchi。少見Clubbing and signs of cor pulmonale.
(3) 可能一開始就hypoxemic respiratory insufficiency, 需要插管。
2. Laboratory features: 起初可能有neutrophilic leukocytosis；大多病人一開始 eosinophil fraction不會高，接會突然高起來。另外ESR與CRP有時也有會高。大部份病人IgE會高。
EVALUATION — 我們會為AEP的病人會有漸近性的喘(一個月內)， 而且chest radiograph有diffuse parenchymal opacities。要問用藥史(如cocaine, gemcitabine, infliximab, ranitidine, venlafaxine), 照過R/T,有寄生蟲/fungus。
1. Laboratory studies: 通常沒啥用。只能用排除其他疾病。
(1)ANCA test for granulomatosis with polyangiitis (Wegener’s) or eosinophilic granulomatosis with polyangiitis (EGPA, Churg Strauss)。但EGPA只有40 to 60%陽性。
(2)IgM and IgG specific for Coccidioides.
(3)Strongyloides or Paragonimiasis
2. Imaging:
(1) 最開始時，only subtle reticular / GGO + Kerley B lines => 疾病進展，bilateral diffuse mixed GGO (也可能會進展成consolidation, 隨機分佈，但疾病惡化後會沿著bronchovascular bundles走) + reticular opacities (共同組成會有crazing paving的感覺)；也可能只有GGO (25%) 或reticular (25%)
(2) diffuse distribution of opacities (重要!!: 不像CEP的分佈: the opacities localized to the lung periphery)
(3) Small pleural effusions are common (70%，後來可能到90%) / bilateral (interstitial 是smooth的)
3. Pulmonary function tests: 進展太快，無法獲得PFT。若辦到了-> restrictive process (reduced FVC & TLC + a normal FEV1/FVC); reduced DLCO
DIAGNOSIS —
(1)主要靠BAL加排除known causes of pulmonary eosinophilia；不太需要lung biopsy
(2)Diagnostic criteria —
a. A febrile illness of short duration (one month or less, but often less than one week)
b. Hypoxemic respiratory failure (eg, pulse oxygen saturation [SpO2] <90 percent on room air or arterial oxygen tension [PaO2] <60 mmHg)
c. Diffuse pulmonary opacities on chest radiograph
d. BAL differential cell count showing eosinophilia >25 percent
e. Absence of known causes of eosinophilic pneumonia, including drugs, infections, asthma, or atopic disease (table 1) (see "Causes of pulmonary eosinophilia")
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