Epidemiology
Etiology
- Combined type III hypersensitivity reaction and type IV hypersensitivity reaction with genetic predisposition
- Inhalation of organic particles (< 5 microns), primarily through occupational exposure
- Farmers are frequently affected
Pathophysiology
Clinical features
- Acute
- Flu-like symptoms: fever, chills, malaise, cough, headache
- Dyspnea without wheezing
- Chest tightness
- Diffuse fine crackles and a late inspiratory squawk upon auscultation
- Symptoms subside within hours to days after removal of the inciting antigen.
- Chronic
- Insidious onset of fatigue, productive cough, progressive dyspnea, cyanosis
- Bilateral rales
- Weight loss
- Due to increased respiratory activity
Diagnostics
High-resolution CT
- Honeycombing (irreversible fibrotic changes) with or without emphysema
- Thickening of alveolar septa
- Traction bronchiectasis or bronchiolectasis
- Ground-glass opacities with inspiratory mosaic attenuation
Lung biopsy
- Supportive findings: noncaseating granulomas with lymphocytes and polynuclear giant cells
Differential diagnostics
- Noncaseating granuloma: vs sarcoidosis
- Clinical features and HRCT: vs idiopathic pulmonary fibrosis
- Affected patients are usually older (eg, age >50) and granulomas are not expected on lung biopsy.