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Eosinophilic lung diseases represent a heterogeneous group of conditions characterized by the accumulation of eosinophils in the alveoli and pulmonary parenchyma.
1. Eosinophilic pneumonia in the course of parasitic infections is likely the most common cause of eosinophilic pneumonia in the world and is mainly due to parasites that migrate through the lungs as they develop (Ascaris lumbricoides, Strongyloides stercoralis, and Ancylostoma duodenale).
Symptoms include cough, rhinitis, loss of appetite, night sweating, low-grade fever, or less frequently wheezing and dyspnea. Eosinophilia in the peripheral blood is common. Sputum should be examined for parasitic larvae. Identification of the worm or ova in stools may be done only several weeks after infestation. Parasite-specific serological assays may be of value. Eosinophilic pneumonia may also be caused by parasites present in the blood or tissues (Toxocara canis, Trichinella spiralis, and taeniasis).
2. Allergic bronchopulmonary aspergillosis (ABPA) is a distinct pulmonary syndrome due to the fungus Aspergillus. ABPA is characterized by asthma, eosinophilia, and bronchiectasis secondary to complex immune-mediated airway reactions to Aspergillus antigens. The disease commonly manifests in patients with established diagnoses of asthma and cystic fibrosis.
Symptoms of ABPA include symptoms of asthma, sometimes with fever and the expectoration of tenacious brown mucus plugs. Chest radiographs reveal damage to the large proximal airways with associated upper-lobe predominant bronchiectasis, mucus plugging, and consequent atelectasis. Acute flares of ABPA are characterized on imaging by fleeting pulmonary opacities due to eosinophilic pneumonia or mucus plugging with regional atelectasis.
1) Atopic asthma or cystic fibrosis.
2) Positive skin prick test results with Aspergillus fumigatus antigens or elevated specific IgE against A fumigatus.
3) Serum IgE >1000 ng/mL.
4) Positive precipitation reaction with A fumigatus antigens.
5) Peripheral eosinophilia >500/mm3.
6) Pulmonary opacities consistent with ABPA.
7) Proximal bronchiectasis (not consistently seen in all patients).
Differential diagnosis includes other types of pulmonary eosinophilia, cryptogenic organizing pneumonia, eosinophilic vasculitis (particularly eosinophilic granulomatosis with polyangiitis [Churg-Strauss syndrome]), and poorly controlled asthma.
Treatment: Oral prednisone 0.5 mg/kg during exacerbations for 14 days followed by a weaning protocol for a total treatment course of 3 to 6 months. Long-term glucocorticoid maintenance therapy is reserved for patients with recurrent exacerbations or with progressive lung injury. Itraconazole can be used as a steroid-sparing agent either as part of an up-front initial combination therapy or in patients demonstrating an inadequate response to glucocorticoids alone.
3. Chronic eosinophilic pneumonia: An idiopathic process that most frequently affects middle-aged women. Approximately 50% and 60% of patients have a preceding history of asthma or atopy. The vast majority of patients are nonsmokers.
Symptoms include fever, night sweats, cough, and weight loss. The disease is characterized by a progressive onset of symptoms over weeks to months. Chest radiographs reveal upper-zone consolidations in the peripheral areas of the lungs (a “photographic negative of pulmonary edema”). Consolidations often do not correspond to anatomical pulmonary segments and are migratory in 25% of patients. Eosinophilia in the peripheral blood is frequent, and significant eosinophilia in the bronchoalveolar lavage (BAL) fluid is present.
Diagnosis is based on the clinical manifestations and presence of eosinophilia; surgical lung biopsy is rarely necessary.
Treatment: Oral prednisone 0.5 mg/kg/day for 2 weeks followed by 0.25 mg/kg/day. Improvement is usually observed within 1 or 2 weeks of treatment initiation, with 80% of patients noting improvement by 48 hours. Continue treatment for ≥6 months while tapering the dose. Patients are at high risk of disease relapse with steroid withdrawal.
4. Acute eosinophilic pneumonia: The etiology is unknown, although a strong association with the initiation of smoking or with numerous environmental exposures has been described.
Symptoms include acute-onset fever, dyspnea, cough, myalgias, and pleuritic pain, although it may also develop subacutely over a few weeks. Patients often develop respiratory failure and require ventilation. Chest radiographs initially reveal fine, disseminated parenchymal lesions that quickly (within hours to 2 days) progress to disseminated consolidations, which are commonly accompanied by pleural effusions. Eosinophilia is very high in BAL and pleural fluids, while eosinophil counts in the peripheral blood are usually normal.
Diagnosis is based on established criteria:
1) Acute onset of febrile respiratory manifestations (≤1 month’s duration).
2) Bilateral diffuse opacities on chest radiography.
3) Hypoxemia with partial pressure of carbon dioxide in the arterial blood (PaO2) on room air <60 mm Hg, and/or PaO2/fraction of inspired oxygen (FiO2) ≤300 mm Hg, and/or oxygen saturation on room air <90%.
4) Lung eosinophilia with >25% eosinophils in the BAL differential cell count.
5) Absence of infection or other known causes of eosinophilic lung disease (especially potential drug reactions).
Treatment: IV methylprednisolone 125 mg every 6 hours until the resolution of respiratory failure followed by prednisone 40 to 60 mg/day, which can be tapered over 2 to 4 weeks. Response is generally observed within 48 hours, allowing rapid weaning from mechanical ventilation if warranted.
5. Eosinophilic bronchitis is characterized by elevated sputum eosinophils and active airway inflammation in the absence of airway hyperresponsiveness. This disease is airway-centered and is a common mimicker of asthma.
Diagnosis is established in the presence of chronic cough, >3% eosinophils in induced sputum, and a negative methacholine challenge test.
Treatment: Inhaled corticosteroids.
6. Other: Chronic eosinophilic leukemia (see Hypereosinophilia), eosinophilic granulomatosis with polyangiitis (Churg-Strauss syndrome).