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NORD is very grateful to Professeur Vincent Cottin, Centre national de reference des maladies pulmonaires rares, Service de pneumologie - Hopital Louis Pradel, Lyon, France, for assistance in the preparation of this report.
Acute eosinophilic pneumonia (AEP) is a rare disorder characterized by the rapid accumulation of eosinophils in the lungs (pulmonary eosinophilia). Eosinophils are a type of white blood cell and are part of the immune system. They are usually produced in response to allergens, inflammation or infection (especially parasitic ones) and are particularly active in the respiratory tract. Common symptoms associated with AEP include progressive shortness of breath (dyspnea) of rapid onset, cough, fatigue, night sweats, low grade fevers, and unintended weight loss. AEP can rapidly progress to cause acute respiratory failure. The exact cause of the disorder is unknown (idiopathic) in many cases.
AEP was first described as a distinct entity in the medical literature in 1989. AEP is classified as a form of eosinophilic lung disease, a large group of interstitial lung diseases. AEP is different from chronic eosinophilic pneumonia (CEP), which is marked by slower progression, lack of progression to acute respiratory failure, frequent relapses and is often associated with asthma. For more information on CEP, choose "chronic eosinophilic pneumonia" as your search term in the NORD Rare Disease Database.
AEP is characterized by a sudden, rapid onset of symptoms usually within 1-7 days. However, in some cases, symptoms may develop less rapidly over the course of up to one month. AEP often develops in young, otherwise healthy individuals. Associated symptoms are nonspecific and can include fevers, cough, difficulty breathing (dyspnea) and chest pain. Less common symptoms include fatigue, muscle pain (myalgia), joint aches, and abdominal discomfort or pain.
AEP can rapidly progress to acute respiratory failure. Acute respiratory failure occurs when the level of oxygen in the blood decreases severely (hypoxemia), potentially resulting in life-threatening breathing complications. This can occur within a few days or even within hours in individuals with AEP. Approximately two-thirds of individuals may require mechanical ventilation.
AEP is an extremely rare disorder and may be confused with infectious pneumonia, which prevents physicians from developing a definitive picture of associated symptoms and prognosis. As AEP becomes better known and more affected individuals are identified, researchers should be able to obtain a better clinical understanding of the disorder. For example, some researchers believe that milder cases of AEP exist, but may go undiagnosed. These mild cases may cause less severe symptoms and complications.
The cause of AEP is unknown (idiopathic). Researchers believe that AEP develops due to an unidentified, nonspecific triggering agent that causes the body to produce eosinophils. The exact reason for the overproduction and accumulation of eosinophils is unknown.
Several environmental factors including occupational factors have been linked to the development of AEP including exposure to dust and smoke. It is unlikely that a single environmental factor causes AEP. Most likely, multiple factors are necessary for the development of the disorder. The triggering factor in AEP can be different from one individual to another.
In many cases, cigarette smoking is believed to play a role in the development of the disorder, specifically in individuals who had just begun smoking within the last three months before the onset of the disorder, have resumed smoking after temporary cessation, or have recently increased the number of cigarettes smoked daily. Several reports in the medical literature have demonstrated an association between cigarette smoking and AEP in a subset of affected individuals. The exact role that smoking plays in the development of AEP in such cases is not fully understood.
Occupational factors that have been linked to the development of AEP are numerous and varied. These cases suggest that breathing in some type of contaminate or inhaled agent that induces damage to the lungs can trigger AEP.
Additional reports in the medical literature have linked some cases of AEP to the use of specific drugs. Drug-induced cases have been linked to daptomycin, an antibiotic, and velafaxine, an antidepressant.
Some researchers believe that cytokines (specialized proteins secreted from certain immune system cells that either stimulate or inhibit the function of other immune system cells) may play a role in the development of eosinophilic disorders. Interleukin-5 (IL-5) is a cytokine that is known to be a regulator of the development and function of eosinophils. It is possible that IL-5 might suppress the normal disintegration (apoptosis) of eosinophils resulting in their accumulation within the lungs and bloodstream. More research is necessary to determine the exact role, if any, of IL-5 in the development of eosinophilic disorders such as AEP.
AEP affects males approximately twice as often as females. Fewer than 100 cases have been reported in the medical literature and the exact prevalence is unknown. AEP can affect individuals of any age, but occurs most often in individuals between 20-40 years of age.
Symptoms of the following disorders can be similar to those of AEP. Comparisons may be useful for a differential diagnosis.
Acute respiratory distress syndrome (ARDS) is a type of severe, acute lung dysfunction affecting all or most of both lungs that occurs as a result of illness or injury. Although it is sometimes called adult respiratory distress syndrome, it may also affect children. Major symptoms may include breathing difficulties (dyspnea), rapid breathing (tachypnea), excessively deep and rapid breathing (hyperventilation) and insufficient levels of oxygen in the circulating blood (hypoxemia). ARDS may develop in conjunction with widespread infection in the body (sepsis) or as a result of pneumonia, trauma, shock, severe burns, aspiration of food into the lung, multiple blood transfusions, and inhalation of toxic fumes, among other things. It usually develops within 24 to 48 hours after the original illness or injury and is a medical emergency. It may progress to failure of other organs. (For more information on this disorder, choose "acute respiratory distress" as your search term in the Rare Disease Database.)
Pneumonia is an infection of the lungs. Symptoms such as fever, cough, large amounts of mucous production (sputum), fluid in the space surrounding the lungs (pleurisy) and/or chills occur. Chest pain, headache, diarrhea, sore throat and fever blisters may also develop. Shortness of breath, difficulty in breathing, decreased exercise tolerance and night sweats are characteristic. Pneumonia frequently occurs in middle-aged to older adults with various underlying diseases. However, it can occur in persons of all ages, statistically most often in winter and early spring. Pneumonia can be caused by various bacteria, viruses, and other infectious agents. AEP can potentially be mistaken for infectious pneumonia.
A diagnosis of AEP is based upon identification of characteristic symptoms, a detailed patient history, a thorough clinical evaluation, and a variety of specialized tests especially bronchoalveolar lavage (BAL). The presence of other causes of pulmonary eosinophilia such as parasitic infections or exposure to certain drugs must be systematically investigated.
Clinical Testing and Work-Up
An exam known as BAL, may be used in the diagnosis of AEP. During a BAL, a narrow tube (flexible bronchoscope) is slid down the windpipe into the lungs and a sterile solution is passed through the tube washing out (lavaging) cells. This fluid is collected and then the tube is removed, allowing the cells to be studied. BAL fluid in individuals with AEP reveals abnormally high levels of eosinophils (greater than 25%).
Specific imaging techniques may be used to help confirm a diagnosis of AEP including chest x-ray, however abnormalities are not specific. Chest x-rays in individuals with AEP generally show white lines or hazy patches (infiltrates) in the lungs.
During the acute phase, pulmonary function tests show a restricted or obstructed pattern.
Individuals with AEP respond rapidly to high doses of corticosteroids for a few weeks. In most cases, there is usually no relapse after steroid therapy is stopped and the prognosis is excellent. Corticosteroid therapy is initiated only after an infectious cause of pulmonary eosinophilia has been ruled out. Within the medical literature, the dose and duration of corticosteroid therapy has varied greatly. Consequently, there is no agreed upon dose or duration for corticosteroid therapy in individuals with AEP. Individuals reported in the medical literature received intravenous corticosteroids initially, followed by oral administration afterward.
Because the disorder often progresses rapidly, many individual require admission into an intensive care unit to receive respiratory support. Respiratory support can consist of either invasive or noninvasive mechanical ventilation. Invasive ventilation provides respiratory support along with an artificial airway, such as one created via a tracheostomy. With a tracheostomy, a tube is surgically implanted into the windpipe (trachea) to maintain an airway. Noninvasive ventilation provides respiratory support via a ventilator without the creation of an artificial airway. Noninvasive ventilation has led to rapid improvement and weaning is often possible in under a week.
In some cases, AEP improves without any treatment (spontaneous remission).
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Report last updated: 2012/03/13 00:00:00 GMT+0