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  • • Eosinophilic pneumonia is defined by the presence of pulmonary infiltrates and the demonstration of either peripheral blood eosinophilia, bronchoalveolar lavage fluid eosinophilia, or lung tissue eosinophilia.
  • • Eosinophilic pneumonia is classified as acute or chronic.
  • • Acute eosinophilic pneumonia presents with the rapid onset of lower respiratory tract symptoms, often culminating in acute respiratory failure.
  • • Chronic eosinophilic pneumonia has a subacute to chronic presentation associated with systemic symptoms and peripheral blood eosinophilia.
  • • Drug toxicity can cause both acute eosinophilic pneumonia and chronic eosinophilic pneumonia and should be ruled out in all cases.

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The eosinophilic pneumonias represent a heterogeneous group of diseases that shares the common feature of eosinophilic infiltration of lung tissue resulting in an airspace pattern on chest radiograph. Generally, the eosinophilia is defined by either: (1) pulmonary infiltrates with peripheral blood eosinophilia, (2) tissue biopsy of the lungs, or (3) bronchoalveolar lavage. Traditionally, eosinophilic pneumonia is divided into acute and chronic forms based on the clinical presentation and course. Acute eosinophilic pneumonia generally occurs in previously healthy individuals and represents a rapidly progressive disease that often culminates in acute respiratory failure. Corticosteroid therapy is very effective and relapse is extremely rare. In contrast, chronic eosinophilic pneumonia presents with a slower onset of symptoms, often in persons with a prior history of asthma or sinusitis. Corticosteroids control the disease but relapses off therapy are common. Careful attention in the history and physical examination should be given to identifying secondary causes of eosinophilic pneumonia such as medication toxicity.

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Acute eosinophilic pneumonia is a rapidly progressive disease generally seen in healthy adults. There is no gender predilection. An association with the acquired immunodeficiency syndrome has been reported.

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Pathogenesis

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There is no known cause of acute eosinophilic pneumonia. It has been speculated that it represents an allergic response to exogenous stimuli. Bronchoalveolar lavage, which samples the alveolar air spaces, has revealed an increased number of eosinophils and an increased concentration of interleukin-5, an eosinophil chemoattractant, in patients with acute eosinophilic pneumonia. Lung biopsy reveals diffuse infiltration of alveolar spaces by eosinophils and alveolar macrophages, accompanied by a proteinaceous exudate, hyaline membranes, and interstitial expansion by eosinophils. In contrast to chronic eosinophilic pneumonia, the alveolar exudate and hyaline membranes imply an acute airspace injury and microabscesses and focal necrosis are not present.

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Clinical Findings

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Acute eosinophilic pneumonia is characterized initially by flu-like symptoms including fever, malaise, myalgias, and cough. Shortness of breath develops rapidly over 1 to 5 days with most patients seeking medical attention within the first week. Physical examination is notable for fever, tachycardia, hypoxia, and crackles on auscultation. Initially chest radiographs may show predominantly an interstitial pattern that rapidly progresses to diffuse, airspace disease. Small pleural effusions have been noted. Laboratory studies are notable for the absence of peripheral blood eosinophilia.

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Differential Diagnosis

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The diagnostic criteria for ...

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