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Acute Eosinophilic Pneumonia
Acute eosinophilic pneumonia (AEP) is a disorder of unknown etiology characterized by rapid eosinophilic infiltration of the lung interstitium (see Overview of Eosinophilic Pulmonary Diseases).
In contrast to chronic eosinophilic pneumonia, AEP is an acute illness that does not usually recur. Incidence and prevalence are unknown. AEP can occur at any age but most often affects patients between 20 and 40 yr, with a male-to-female ratio of 21:1. The cause is unknown, but AEP may be an acute hypersensitivity reaction to an unidentified inhaled antigen in an otherwise healthy person. Cigarette or other smoke exposure may be involved.
AEP causes an acute febrile illness of short duration (usually < 7 days). Symptoms are nonproductive cough, dyspnea, malaise, myalgias, night sweats, and pleuritic chest pain. Signs include tachypnea, fever (often > 38.5° C), and bibasilar inspiratory crackles and, occasionally, rhonchi on forced exhalation. Patients with AEP frequently present with acute respiratory failure requiring mechanical ventilation. Rarely, distributive (hyperdynamic) shock can occur.
The diagnosis is suspected in patients with symptoms of acute pneumonia that progresses to respiratory failure and does not respond to antibiotics. Diagnosis is based on findings from routine testing and is confirmed by bronchoscopy. AEP is a diagnosis of exclusion and requires the absence of known causes of eosinophilic pneumonia (eg, drug- and toxin-induced, helminthic and fungal infection–related, eosinophilic granulomatosis with polyangiitis [Churg-Strauss syndrome], idiopathic hypereosinophilic syndrome, tumors). The CBC often fails to demonstrate markedly elevated eosinophil counts, unlike in chronic eosinophilic pneumonia. ESR and IgE levels are high but are nonspecific.
The chest x-ray initially may show only subtle reticular or ground-glass opacities, often with Kerley B lines. Isolated alveolar (about 25% of cases) or reticular (about 25% of cases) opacities may also be observed. Unlike in chronic eosinophilic pneumonia, in AEP opacities are not characteristically localized to the lung periphery. Small pleural effusions occur in two thirds of patients and are frequently bilateral.
HRCT is always abnormal with bilateral, random, patchy ground-glass or reticular opacities.
Pleural fluid examination shows marked eosinophilia with high pH. Pulmonary function tests often show a restrictive process with reduced diffusing capacity for carbon monoxide (DL co ).
Bronchoscopy should be done for lavage and, occasionally, biopsy. Bronchoalveolar lavage fluid often shows a high number and percentage (> 25%) of eosinophils. The most common histopathologic features on biopsy include eosinophilic infiltration with acute and organizing diffuse alveolar damage, but few patients have undergone lung biopsy.
Some patients improve spontaneously. Most are treated with prednisone 40 to 60 mg po once/day. In patients with respiratory failure, methylprednisolone 60 to 125 mg IV q 6 h is preferred. The prognosis is usually good; response to corticosteroids and complete recovery is common. Pleural effusions resolve more slowly than parenchymal opacities.
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