Hypereosinophilic lung diseases - Acute idiopathic eosinophilic pneumonia
Dr Ian Glaspole MBBS PhD FRACP Respiratory Physician. Alfred Hospital, Prahran 3181
Description: Acute eosinophilic pneumonia is a condition characterised by the accumulation of eosinophils within the lung. Most patients who develop the condition are aged between 20 and 40 years, with men being affected approximately twice as frequently as women.
Epidemiology and diagnosis: The cause for acute eosinophilic pneumonia is unknown. It may reflect an acute hypersensitivity reaction to an unidentified inhaled antigen, with the condition being noted to occur in situations where patients have been exposed to unusual inhaled antigens, such as around the time of the World Trade Centre disasters, or with the new onset of cigarette smoking.
At its onset, an acute febrile illness with generalised symptoms such as malaise, muscle aches, and night sweats may occur. Usually within the first week of illness, respiratory symptoms occur, including cough, breathlessness and pleuritic chest pain. The condition usually progresses rapidly, and the majority of patients develop respiratory failure, leading to the need for oxygen and sometimes mechanical ventilation.
Blood tests demonstrate elevation of the eosinophil count and usually the neutrophil count. The ESR is elevated. The IgE level is also high in the majority of patients. Chest x-ray may demonstrate initially e only subtle haziness but as the disease advances, more pronounced diffuse opacification of both lungs is seen. Small pleural effusions (collections of fluid in the space between the lung and chest wall) are frequently seen. High resolution CT scans are always abnormal and demonstrate involvement of the alveolar walls and air spaces. At bronchoscopy, specimens reveal elevation of the number of eosinophils, and frequently lymphocyte and neutrophil proportions are also increased. Surgical lung biopsy demonstrates diffuse alveolar damage and the presence of increased numbers of alveolar eosinophils.
Management: Where acute eosinophilic pneumonia is suspected other causes of lung eosinophilia should be excluded. Other causes for lung eosinophilia include asthma, allergic bronchopulmonary aspergillosis, parasitic infection, fungal infection, certain medications, and inhalational injury. Most patients with acute eosinophilic pneumonia demonstrate progressive respiratory failure. The condition almost always rapidly responds to intravenous or oral corticosteroid therapy. Frequently high doses of steroids are required. For those patients in respiratory failure, therapy is usually started with intravenous treatment. After several days, therapy can usually be switched to oral treatment which is administered in a tapering regimen over a period of several months, with the total duration being guided by the patient's response.
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