By Dr. Michael Wechsler
Division of Pulmonary and Critical Care
Brigham and Women’s Hospital
Harvard Medical School
There are 2 main types of eosinophilic pneumonias, acute and chronic. While both are characterized by eosinophil invasion of the lung tissue, they are quite different from one another and described below.
Acute eosinophilic Pneumonia
First described in the 1980’s, acute(develops suddenly) eosinophilic pneumonia is characterized by fevers, difficulty breathing, respiratory failure that may require mechanical ventilation, abnormal chest xray, inflammation throughout the lungs, and pulmonary eosinophilia in a previously healthy individual (Table 1).
At presentation, it is often mistaken for acute lung injury or acute respiratory distress syndrome (ARDS), until a bronchoalveolar lavage (fluid washed from airways) is performed and reveals >25% eosinophils. The main symptoms of acute eosinophilic pneumonia are cough, shortness of breath, fatigue, muscle aches, night sweats and chest pain worsened by breathing. Exam findings include high fevers and abnormal lung sounds. Acute eosinophilic pneumonia most often affects males between age 20 and 40 with no history of asthma. While no clear etiology has been identified, several case reports have linked acute eosinophilic pneumonia to recent initiation of tobacco smoking (JAMA 2005), or exposure to other environmental stimuli including dust from indoor renovations (PhilitAJRCCM 2002), or even World Trade Center dust (ROM AJRCCM 2002).
In addition to a suggestive history, the key to establishing a diagnosis of acute eosinophilic pneumonia is the presence of >25% eosinophilia on bronchoalveolar lavage fluid from the lungs. Lung biopsy is not always necessary to make a diagnosis. While patients present with an elevated white blood cell count, in contrast to other pulmonary eosinophilic syndromes, acute eosinophilic pneumonia is often not associated with high eosinophil levels in the blood at first. However, between 7 and 30 days, blood eosinophil levels become elevated. CT scans of the chest are always abnormal with patchy opacities in both lungs, and small amounts of fluid around the lung in many.
Treatment & Prognosis
While some patients improve without specific treatment, most patients require admission to an intensive care unit and respiratory support with either invasive (intubation) on noninvasive mechanical ventilation. Usually just the lungs are affected, with normal function of other organs. Acute eosinophilic pneumonia is very responsive to steroids and the prognosis is excellent. Another distinguishing feature of acute eosinophilic pneumonia is the complete recovery of both symptoms and x-ray abnormalities without recurrence or residual sequelae, within weeks of treatment.
Table 1 Diagnostic criteria of Acute Eosinophilic Pneumonia
Acute febrile illness with respiratory manifestations of <1 month duration
Hypoxemic respiratory failure (inability to breathe, low oxygen levels)
Diffuse pulmonary infiltrates on chest x-ray (abnormal x-ray)
Lung fluid eosinophilia>25%
Absence of parasitic, fungal or other infection
Absence of drugs known to cause pulmonary eosinophilia
Quick clinical response to corticosteroids
No recurrence after discontinuation of corticosteroids
Chronic Eosinophilic Pneumonia
aChronic eosinophilic pneumonia is characterized by pulmonary infiltrates and eosinophilia in both the tissue and blood (see table ). Most patients are middle age female nonsmokers and patients do not usually develop the severe sudden illness seen in acute eosinophilic pneumonia. Similar to Churg-Strauss Syndrome, a majority have asthma, with many having a history of allergies; the airflow obstruction tends to worsen with disease activity, but responds similarly to corticosteroids.
Patients present with illness occurring over weeks to months, with cough, low grade fevers, progressive shortness of breath, weight loss, wheezing, fatigue and night sweats, and a chest x-ray with migratory abnormalities.
Almost 90% of patients have high blood levels of eosinophils, with mean eosinophil counts of over 30% of total white blood cell count. Lung fluid from the bronchii also shows high numbers of eosinophils, close to 60%. The high levels of eosinophils respond to treatment with corticosteroids. Lung biopsy is also often not required to establish a diagnosis.
Treatment & Prognosis
Similar to acute eosinophilic pneumonia, non-respiratory manifestations are uncommon but joint pain, nerve damage and skin and gastrointestinal symptoms have all been reported; their presence may suggest another eosinophil associated disease like CSS or HES. Chronic eosinophilic pneumonia responds rapidly to corticosteroids with quick resolution of lung and blood eosinophils, and improvement in symptoms. However, over 50 % of patients have recurrent eosinophilic pneumonia, and many require prolonged courses of corticosteroids for months to years.
Table: Chronic eosinophilic pneumonia
- Respiratory symptoms of usually more than 2 weeks duration
- Lung and/or blood eosinophilia
- Pulmonary infiltrates on x-ray
- Exclusion of any known cause of eosinophilic lung disease.
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