Chronic eosinophilic pneumonia is a rare disorder characterized by the appearance of dyspnea, cough, and constitutional symptoms as a response to an abundance of eosinophils in the lungs. The cause remains to be determined, but many patients suffer from asthma, suggesting an immune-mediated pathogenesis. Clinical criteria, laboratory workup identifying eosinophilia, and imaging studies in the form of X-rays and computed tomography, are used to make the diagnosis.
Chronic eosinophilic pneumonia (CEP) is an interstitial lung disorder of unknown etiology (often termed idiopathic CEP in the literature) that is characterized by a profound deposition of eosinophils in the lungs and the subsequent development of symptoms     . CEP is most frequently diagnosed in adults around 50 years of age with a significant predilection toward female gender . Although a clear association has not been described, a large number of individuals suffer from asthma or some other form of atopy (such as allergic rhinitis)    . Additionally, isolated studies have identified radiation therapy for breast cancer as a possible risk factor . The clinical presentation is distinguished by a cough, wheezing, and progressive dyspnea as main respiratory complaints that may be accompanied by constitutional symptoms - weight loss, fever, and night sweats    . In rare cases, massive eosinophilic infiltration can lead to respiratory insufficiency, but most patients suffer from a milder form of the disease  . CEP usually has a slow course, and several weeks might pass before the diagnosis is made  .
A thorough workup is necessary in the case of CEP, encompassing clinical, radiologic, and possibly histopathologic studies. They are all necessary for narrowing the broad differential diagnosis, which includes pulmonary infections (both parasitic and fungal), iatrogenic causes, neoplastic processes, autoimmune vasculitis (Churg-Strauss syndrome), and several other entities that induce pulmonary eosinophilia   . Obtaining a complete patient history that will identify basic characteristics of symptoms and their duration is the first step, followed by a detailed personal history. A meticulous physical examination should follow, although lung auscultation may not yield any pathological findings. For this reason, laboratory and imaging studies are the cornerstones in making an initial diagnosis. Detection of peripheral eosinophilia (often exceeding ≥ 1000/mm3) in blood, but also in the bronchioalveolar aspirate (obtained through a bronchioalveolar lavage, or BAL) is a valid diagnostic clue, whereas serum inflammatory markers (erythrocyte sedimentation rate and C-reactive protein), but also immunoglobulin E levels, are often elevated   . Conversely, the presence of bilateral infiltrates and ground-glass opacities at the peripheries is typical for CEP, which can be better visualized on computed tomography (CT) compared to standard X-rays of the chest     . Although not necessary and now rarely used for confirmation of CEP, bronchoscopy and subsequent biopsy with histopathological examination is useful for excluding other disorders, as the accumulation of eosinophils in the alveoli and the interstitium is the hallmark of CEP  . Pulmonary function tests are not always abnormal, but several studies have identified a reduced ability of the lungs to transfer oxygen into the blood, known as the diffusing capacity of the lung for carbon monoxide (DLCO)  .