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Current Concepts in

HYPERSENSITIVITY PNEUMONITIS

Karen A. Wong, MD

PGY5, Pulmonary & Critical Care

Overview:

  • Introduction
  • Epidemiology
  • Pathophysiology
  • Classification & Diagnosis

* 2020 ATS/JRS/ALAT Guidelines

  • Screening & Prevention
  • Management
  • Future Directions

Hypersensitivity pneumonitis (HP)

  • AKA extrinsic allergic alveolitis

  • Immune-mediated ILD in susceptible/sensitized patients

  • Caused by repeated inhalation of/sensitization to wide variety of inhaled antigens

  • Clinical presentation & course high variable

Epidemiology

  • Accounts for 2-47% all ILD cases

  • Annual incidence of 1.28-1.94 per 100K and prevalence of 1.67-2.71 per 100K in USA

  • Increased incidence with increasing age; mean age at dx 50-60yo

  • 58% female predominance in USA

  • Less frequently seen in former/active smokers

Pathophysiology

  • Inciting antigens:
  • Microbes
  • Animal proteins
  • Low molecular weight chemicals

Bird Breeder's/Fancier's Lung

Farmer's Lung

Humidifier Lung

  • Sources:
  • Hay exposure
  • Thermophilic actinomyces
  • Fungi
  • Compost
  • Maize corn
  • Sources:
  • Feather dust
  • Avian excrement & serum

  • Pigeons, parakeets, canaries, parrots, cockatiels, lovebirds

  • Feather duvet lung & cross-reactivity

  • Lingering occult exposure
  • Sources:
  • Contaminated humidifiers/AC
  • Thermophilic actinomyces
  • Bacteria/molds/yeast

Subtypes of HP

  • Previous classification:
  • ACUTE
  • SUBACUTE
  • CHRONIC

  • Proposed new classification:
  • FIBROTIC HP
  • NON-FIBROTIC HP

Clinical Presentation

  • Dyspnea, cough, chest tightness, wheezing
  • Midinspiratory squeaks
  • Constitutional symptoms

  • Timing
  • Acute (days to weeks, occasionally with pleural effusion)
  • Insidious (worsening over months to years)
  • Recurrent/episodic exacerbations

Diagnosis of HP

DEFINITE HP (>=90% confidence)

HIGH-CONFIDENCE FOR HP (80-89%)

MODERATE-CONFIDENCE (70-79%)

LOW CONFIDENCE (51-69%)

1) Exposure identification

  • HPI +/- clinical questionnaire
  • Serum IgG testing +/- inhalational challenge

2) Chest HRCT pattern

3) Bronchoscopic & histopathologic findings

Radiologic Features of Non-Fibrotic HP

centrilobular nodules

mosaic attenuation

air trapping on expiratory scan

uniform, subtle GGOs and cysts

Radiologic Features of Fibrotic HP

coarse reticulation, minimal honeycombing

in random axial distribution

GGOs

Lobules of decreased

attenuation/vascularity

Normal lung

fibrotic GGA alone or with

small airways disease

central/peribronchovascular predominance

small airways disease

upper lung zone predominance

Histopathologic Features of

Non-Fibrotic/Cellular HP

chronic interstitial pneumonia around bronchioles

cellular bronchitis , primarily lymphocytic

poorly formed non-necrotizing granuloma

Histopathologic Features of

Non-Fibrotic/Cellular HP

RLL surgical lung biopsy with patchy fibrosis and architectural distortion

Schaumann body

Adjunct Testing

  • Pulmonary Function Testing
  • Restrictive ventilatory pattern, with reduced FVC, TLC
  • Can see mixed obstructive/restrictive pattern
  • DLCO reduced in all forms of hypersensitivity pneumonitis
  • Many patients have hypoxemia at rest; most patients desaturate with exercise

  • Bronchoalveolar lavage
  • Acute phase: >5% PMNs, usually followed by marked lymphocytosis (at least 20% lymphocytes, usually >50%)
  • Can see mast cells (esp acute, within 3mos of exposure), eos, plasma cells
  • High levels of IgA/IgG/IgM/free light chains with plasma cells supports active HP
  • CD4/CD8 ratio controversial
  • Ratio <1.0 consistent with acute/subacute disease, higher ratio occurs most often in chronic disease
  • Depends on type of antigen, severity of exposure, disease stage

Prevention

  • Avoiding/decrease exposure to inciting antigens is cruit to preventing HP

  • Occupational exposures: routine inspections, remove from environment

  • Antimicrobial solutions to reduce thermophilic actinomycetes (e.g. in bagassosis, during sugar cane processing)

  • Drain humidifiers daily, remove water-damaged furnishings

  • PPE!

Management of HP & Future Directions

  • Complete antigen avoidance

  • Corticosteroids
  • Acute symptomatic relief; may accelerate the initial recovery in persons with severe disease
  • Prednisone 0.5-1mg/kg/2 x 1-2 weeks for acute, 4-8 weeks for subacute/chronic
  • Followed by gradual taper to off or maintenance dosing 10mg/d
  • Guided by clinical response, PFTs, radiographic improvement

  • ICS, bronchodilators, cromolyn, antihistamines --> maybe helpful for reactive airways/obstruction
  • Low dose macrolides for antiinflammatory effect?

  • Azathioprine, cyclosporine, MMF --> unclear in adults

  • Anti-fibrotics?

  • Lung transplant

Takeaways

  • HP is an immune mediated ILD seen in sensitized/susceptible individuals

  • Many sources of inhaled antigens
  • Microbes, yeasts, animal/plant proteins, particulate matter, drugs

  • Proposed classification of non-fibrotic vs. fibrotic HP

  • Dx based on history/exposure, with combination of serum testing/provocation, BAL (lymphs!), HRCT findings, histopathology
  • To biopsy or not to biopsy?

  • Mgmt: AVOID EXPOSURES, corticosteroids, xplant
  • Antifibrotics? Genetic susceptibility testing

Thank you!

Thank you!

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