Pneumonitis, Hypersensitivity

Key Features

Essentials of Diagnosis

• A link between symptoms and antigen exposure may be obtained from work or environmental history

• Antigen can be microbial agents, animal proteins, or chemical sensitizers

• Presentation can be acute or subacute illness

General Considerations

• 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 9–23

  • 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)

Clinical Findings

Symptoms and Signs

• Acute illness 4–8 hours after exposure characterized by

  • Malaise

  • Chills

  • 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

  • Anorexia

  • Weight loss

Differential Diagnosis

• Sarcoidosis

• Asthma

• Atypical pneumonia

• Collagen vascular disease, eg, systemic lupus erythematosus

• Idiopathic pulmonary fibrosis

• Lymphoma

Diagnosis

Laboratory Tests

• Pulmonary function studies show a restrictive pattern with decreased diffusion capacity

• WBC 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

Imaging Studies

• Chest radiograph classically shows small nodular densities sparing the apices and bases

• Pulmonary fibrosis may be found with repeated exposure to the offending agent

Diagnostic Procedures

• Bronchoscopy with bronchoalveolar lavage

• Surgical lung biopsy may be necessary

Treatment

Medications

• Corticosteroids (prednisone, 0.5 mg/kg/day as single morning dose for 2 weeks, tapered to nil over 4–6 weeks)

Therapeutic Procedures

• Identification of ...