Eosinophilic pneumonia overview

# Overview
Eosinophilic pneumonia (EP) is a disease in which a certain type of white blood cell called an eosinophil accumulates in the lung. These cells cause disruption of the normal air spaces (alveoli) where oxygen is extracted from the atmosphere. Several different kinds of eosinophilic pneumonia exist and can occur in any age group. The most common symptoms include cough, fever, difficulty breathing, and sweating at night. EP is diagnosed by a combination of characteristic symptoms, findings on a physical examination by a health provider, and the results of blood tests and x-rays. Prognosis is excellent once most EP is recognized and treatment with corticosteroids is begun.

# Historical Perspective
In 1944, Hamman described a group of four otherwise healthy patients who developed progressive lung disease, known as Hamman-Rich syndrome. In 1989, acute eosinophilic pneumonia was first described by Badesch and colleagues. In 1969, Carrington was the first to describe chronic eosinophilic pneumonia and known as Carrington syndrome.

# Classification
Eosinophilic lung diseases may be classified according to the cause into pneumonia of unknown cause such as idiopathic chronic eosinophilic pneumonia and idiopathic acute eosinophilic pneumonia, pneumonias of known cause such as allergic bronchopulmonary aspergillosis, eosinophilic pneumonias of parasitic origin, and eosinophilic airways diseases such as hypereosinophilic asthma and idiopathic hypereosinophilic constrictive bronchiolitis.

# Pathophysiology
Eosinophils migrate to inflammatory sites in tissues in response to chemokines like CCL11, CCL24, CCL5,, and certain leukotrienes like leukotriene B4. When eosinophils are activated, they release eosinophilic granules. Following activation, eosinophils effector functions include production of reactive oxygen products such as superoxide and peroxide produced by eosinophil peroxidase, growth factors such as TGF beta and cytokines such as IL-1, IL-2, and TNF alpha.

# Causes
Causes of eosinophilic lung diseases are acute eosinophilic pneumonia, chronic eosinophilic pneumonia, tropical pulmonary eosinophilia, eosinophilic granulomatosis with polyangitis, allergic bronchopulmonary aspergillosis, and medications such as nonsteroidal anti-inflammatory drugs, anticonvulsants, antidepressants, angiotensin converting enzyme inhibitors, and beta blockers.

# Differentiating  from other Diseases
Acute eosinophilic pneumonia may be differentiated from other causes of pulmonary eosinophilia such as acute eosinophilic pneumonia, the transpulmonary passage of helminth larvae (Loffler syndrome), tropical pulmonary eosinophilia, eosinophilic granulomatosis with polyangiitis, allergic bronchopulmonary aspergillosis, and drugs and toxins.

# Epidemiology and Demographics
The prevalence of idiopathic chronic eosinophilic pneumonia (ICEP) remains unknown. The incidence of chronic eosinophilic pneumonia in an Icelandic registry was 0.23 cases/100,000 population per year between 1990 and 2004. ICEP has been reported to contribute to 0 to 2500 per 100,000 of cases included in different registries of interstitial lung diseases. There is no racial predilection for ICEP. Women are more commonly affected by ICEP than men. ICEP typically affects patients in their 30s or 40s.

# Risk Factors
Risk factors for eosinophilic pneumonia vary according to the type; acute pneumonia is related to the recent initiation of tobacco smoking. One third to one-half of the chronic pneumonia patients have a history of asthma.

# Screening
There is no specific screening for eosinophilic pneumonia.

# Natural History, Complications and Prognosis
If left untreated, patients with eosinophilic pneumonia may progress to develop dyspnea, pleural effusion, and respiratory failure. Common complications of eosinophilic pneumonia include respiratory failure, relapse, and adverse effects of steroids. Prognosis is generally excellent, and only a couple of lethal cases have been reported.

# Diagnostic Criteria
Diagnostic criteria of idiopathic chronic eosinophilic pneumonia include diffuse pulmonary alveolar consolidation, eosinophilia at bronchoalveolar lavage, respiratory symptoms present for at least 2 to 4 weeks, and absence of other known causes of eosinophilic lung disease. Idiopathic acute eosinophilic pneumonia criteria are acute onset with febrile respiratory manifestations, bilateral diffuse infiltrates on imaging, lung eosinophilia, with 25% eosinophils at bronchoalveolar lavage, and absence of determined cause of acute eosinophilic pneumonia.

# History and symptoms
Onset of chronic type is more than 2-4 weeks and acute one is less than 1 month. A history of atopy is found in 60 percent. Symptoms of idiopathic eosinophilic pneumonia include dyspnea, fever, cough, wheezing, sputum, myalgias.

# Physical Examination
Physical examination may reveal fever or sometimes low body temperature, an increased respiratory rate, low blood pressure, a fast heart rate, or a low oxygen saturation, which is the amount of oxygen in the blood as indicated by either pulse oximetry or blood gas analysis. Patients who have difficulty breathing, who are confused, or who have cyanosis (blue-tinged skin) require immediate attention. Auscultation findings include lack of normal breath sounds, the presence of crackling sounds (rales), or increased loudness of whispered speech (whispered pectoriloquy) with areas of the lung that are stiff and full of fluid, called consolidation. Vital signs are useful in determining the severity of illness and have predictive values. However, a high degree of suspicion should be kept in elderly as the presentation could be subtle in them.

# Laboratory Findings
No laboratory studies are specific for acute or chronic eosinophilic pneumoina. The usual laboratory tests include complete blood count, pulmonary function tests, liver function tests, renal function tests, and tests to exclude other causes of pulmonary eosinophilia.

# X-ray
The chest x-ray of eosinophilic pneumonia may show reticular or ground glass opacities. The distribution of opacities is localized to the lung periphery in acute pneumonia and diffuse in chronic one.

# CT
Characteristic CT findings of CEP include ground-glass attenuation, consolidation, nodules, septal thickening, pleural effusions, and thickening of bronchovascular bundles.

# Other imaging Studies
Thoracic US can be used to follow-up patients with acute eosinophilic pneumonia. The US shows that all patients exhibited multiple diffuse bilateral B-lines and lung sliding which was consistent with the alveolar-interstitial syndrome. B-line numbers fell during the course of treatment. The US is a useful modality for evaluating the treatment response in patients with acute eosinophilic pneumonia.

# Other diagnostic studies
In acute eosinophilic pneumonia (AEP), Pulmonary function tests show reduced forced vital capacity and total lung capacity with a normal forced expiratory volume in one second; diffusing capacity for carbon monoxide (DLCO) is commonly reduced. Bronchoalveolar lavage (BAL) is performed in the majority of patients to exclude infection, hemorrhage, or malignancy. The BAL is performed using a sequential installation and recovery of 50 to 60 mL. The median BAL cellularity was 350,000/mm3. BAL eosinophilia was present in all cases with a median of 38%. Lung biopsy is rarely necessary to make a diagnosis of AEP in immunocompetent patients with a compatible history and prominent BAL eosinophilia in the absence of infection or another known precipitant.

# Medical Therapy
Medical treatment of eosinophilic pneumonia include supportive care with supplemental oxygen, empiric antibiotics until culture results are available, and systemic glucocorticoid therapy, systemic glucocorticoids for almost all patients except those with clear evidence of an improving course. Prednisone is the preferred drug of choice. The dose of 40 to 60 mg daily is reasonable. Glucocorticoid tapering over 7 to 14 days may be acceptable for patients who present with initial eosinophilia. If a patient fails to respond to glucocorticoids, an alternative diagnosis should be used such as subcutaneous interferon, high-dose intravenous immunoglobulins, plasma exchange. Relapse can be treated with a dose of 20 mg per day of prednisone.

# Surgery
Surgery is not indicated for eosinophilic pneumonia.

# Primary Prevention
Relapses occur in more than half the patients while decreasing or after stopping corticosteroids. Relapses typically can be treated with a dose of 20 mg per day of prednisone.

# Secondary Prevention
There are no established measures for the secondary prevention of eosinophilic pneumonia.