Hypersensitivity Pneumonitis - Extrinsic Allergic Alveolitis

Hypersensitivity pneumonitis has several synonyms, including hypersensitivity syndrome and extrinsic allergic alveolitis.

Etiologies

• Thermophilic actinomyces – farmer lung, bagassosis 
• Fungi/mold – maple bark disease, malt-worker lung
• Animal proteins – pituitary snuff-taker lung, pigeon breeder disease
• Chemicals – bathtub finisher lung

Pathophysiology

• Type III immune complex disease
• Also includes type IV cell-mediated immunity
• Inhaled antigen acts upon alveolar macrophages to activate them and causes the release of enzymes which results in inflammation and fibrosis

Clinical Presentation

• Chills, fever
• Dyspnea, cough, airway obstruction
• Weight loss
• Disease process may be progressive with eventual fibrotic lung disease

Diagnosis

• Early identification of hypersensitivity is crucial for removal of offending antigens and initiation of treatment
  • Suspect in patients with recurring pneumonias or pneumonitis
• Laboratory testing
  • Serum precipitating antibodies
• Imaging studies
  • Chest X-ray – ground glass appearance suggesting pneumonia

Treatment

• Removal from antigen exposure
• May require corticosteroid therapy 

Indications for Ordering

• Tests generally appear in the order most useful for common clinical situations
• Click on number for test-specific information in the ARUP Laboratory Test Directory