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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)

Table 9–23.Selected causes of hypersensitivity pneumonitis.

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 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 the offending agent with removal or avoidance

  • Change in occupation is often unavoidable

Outcome

Follow-Up

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