chronic hypersensitivity pneumonitis

Introduction

A chronic progressive form of pneumonitis which occurs after exposure to a variety of antigens, including occupational antigens (i.e. farmer's lung, pigeon breeder's lung, byssinosis etc.).

Pathology

• granulomatous reaction with round cell infiltrates, epithelioid cells
• septal swelling with lymphocytes & plasma cells
• foamy macrophages with interstitial granulomas (pigeon breeder's lung)

Clinical manifestations

• symptoms are insidious in onset
• symptoms are progressive eventually resulting in pulmonary fibrosis
• clinically identical to idiopathic pulmonary fibrosis

Laboratory

• bronchoalveolar lavage (BAL) may show reversal of CD4/CD8 ratio
• lung biopsy
• positive serology is not diagnostic
  • 20% of asymptomatic farmers have positive precipitins
  • 40% of asymptomatic pigeon breeder's have positive precipitins
  • 10% of symptomatic farmers have negative precipitins

Diagnostic procedures

Pulmonary function testing:

• decreased lung volumes
• decreased lung compliance
• decreased DLCO
• exercise-induced hypoxemia

Management

• avoid exposure to causative precipitins
• corticosteroids

More general terms

• hypersensitivity pneumonitis
• chronic lung disease

Additional terms

• idiopathic pulmonary fibrosis (IPF); usual interstitial pneumonitis (UIP)