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Hypersensitivity Pneumonitis

Immune-mediated interstitial lung disease from inhaled antigen exposure

Written by: Saygı Hospital Health Guide Editorial Board
Published:

This content is for general information; please consult your physician for diagnosis and treatment.

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What is Hypersensitivity Pneumonitis?

Hypersensitivity pneumonitis (HP), also called extrinsic allergic alveolitis, is an immune-mediated inflammatory and often fibrotic interstitial lung disease caused by inhalation of antigens from organic sources (bird proteins, molds, bacteria) or low-molecular-weight chemicals (isocyanates) in genetically susceptible individuals.

Pathophysiology involves a combination of type III (immune complex) and type IV (cell-mediated) hypersensitivity reactions with granulomatous inflammation centered on bronchioles and alveoli. Repeated antigenic exposure may lead to progressive fibrosis.

Current classification divides HP into non-fibrotic (predominantly inflammatory) and fibrotic forms based on radiographic and histopathologic findings. Fibrotic HP resembles IPF and carries worse prognosis; non-fibrotic HP often improves with antigen avoidance.

Diagnosis integrates exposure history, characteristic HRCT findings (centrilobular ground-glass nodules, mosaic attenuation with air trapping, fibrotic changes), bronchoalveolar lavage lymphocytosis, specific serum IgG antibodies, and when needed, transbronchial or surgical lung biopsy.

Symptoms

Acute form: influenza-like symptoms 4-8 hours after exposure with cough, dyspnea, fever, chills, myalgia
Subacute form: progressive dyspnea, cough, fatigue, weight loss over weeks to months
Chronic form: insidious progressive exertional dyspnea, cough, weight loss, clubbing
Bibasilar inspiratory crackles and squawks on auscultation
Reduction in exercise tolerance and gas exchange abnormalities
Resolution with antigen avoidance in non-fibrotic disease; persistence or progression in fibrotic HP

Risk Factors

Farmer's lung (moldy hay — thermophilic actinomycetes)
Bird fancier's / pigeon breeder's lung (avian proteins in droppings, feathers)
Hot tub lung (Mycobacterium avium complex aerosols)
Occupational: chemical workers (isocyanates), metalworkers, woodworkers
Domestic mold exposure, humidifier contamination, feather-filled bedding
Genetic susceptibility: HLA-DRB1 variants, MUC5B promoter polymorphism

When to See a Doctor?

If you experience any of the following symptoms, seek medical attention promptly:

  • Recurrent flu-like symptoms with cough and dyspnea following specific environmental exposures warrant medical evaluation and exposure history.
  • Progressive dyspnea, persistent cough, or weight loss in individuals with relevant occupational or environmental exposures requires pulmonary assessment.
  • Known HP patients with worsening respiratory symptoms despite exposure avoidance need urgent re-evaluation for progression or alternative diagnosis.

Treatment Methods

01
Complete antigen avoidance is the cornerstone of management; identify and eliminate the offending exposure through detailed environmental history.
02
Systemic corticosteroids (prednisone 0.5-1 mg/kg/day with gradual taper) for symptomatic non-fibrotic HP and acute exacerbations.
03
Immunosuppressive agents (mycophenolate, azathioprine) for steroid-sparing in chronic or relapsing disease.
04
Antifibrotic therapy (nintedanib) for fibrotic HP demonstrating progressive pulmonary fibrosis despite antigen avoidance.
05
Supportive care: supplemental oxygen for hypoxemia, pulmonary rehabilitation, influenza and pneumococcal vaccination.
06
Lung transplantation evaluation for end-stage fibrotic HP with refractory progression and functional decline.

Which Department to Visit?

You can visit our Göğüs Hastalıkları department for these complaints. Our specialist physicians will create the most suitable treatment plan for you.

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Health Disclaimer: The information on this page is prepared for general informational purposes only. It does not replace medical diagnosis and treatment. Please consult your physician for your complaints. Saygı Hospital does not accept responsibility for actions taken based on the information on this page.