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Essentials of Diagnosis
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A link between symptoms and antigen exposure may be obtained from work or environmental history
Exposure to inhaled microbial, avian, and animal antigens, and less commonly to an inorganic agent
Presentation can be acute or subacute illness
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General Considerations
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A nonatopic, nonasthmatic inflammatory pulmonary disease (also called extrinsic allergic alveolitis)
Manifested mainly as occupational disease where exposure to an inhaled organic antigen leads to an acute illness
Causes
See Table 9–21
Farmer's lung (moldy hay)
"Humidifier" lung (contaminated humidifier, heating, or air conditioning)
Bird fancier's lung ("pigeon breeder's disease")
Bagassosis (moldy sugar cane fiber)
Sequoiosis (moldy redwood sawdust)
Maple bark stripper's disease
Mushroom picker's disease (moldy compost)
Suberosis (moldy cork dust)
Detergent worker's lung (enzyme additives)
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Acute illness 4–8 hours after exposure characterized by
Malaise
Chills
Low-grade fever
Cough
Dyspnea
Nausea
Bibasilar crackles, tachypnea, tachycardia, and (occasionally) cyanosis are found
Subacute and chronic illness (15% of cases)
Insidious onset of chronic cough and progressive dyspnea
With continued exposure, slowly progressive dyspnea
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Differential Diagnosis
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Sarcoidosis
Asthma
Atypical pneumonia
Collagen vascular disease, eg, systemic lupus erythematosus
Idiopathic pulmonary fibrosis
Lymphoma
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Pulmonary function tests show a restrictive pattern with reduced diffusing capacity
White blood count shows leukocytosis with a left shift
Arterial blood gases show hypoxemia
Hypersensitivity pneumonitis antibody panels are available; positive results while supportive do not establish a definitive diagnosis
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Chest radiograph classically shows small nodular densities sparing the apices and bases
Pulmonary fibrosis may be found with repeated exposure to the offending agent
High-resolution CT findings of non-fibrotic disease include upper-/mid-lung ground glass or nodular opacities and signs of air trapping
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Diagnostic Procedures
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