HYPERSENSITIVITY PNEUMONITIS
Karen A. Wong, MD
PGY5, Pulmonary & Critical Care
- 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
- 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
- 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
- Previous classification:
- ACUTE
- SUBACUTE
- CHRONIC
- Proposed new classification:
- FIBROTIC HP
- NON-FIBROTIC HP
- 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
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
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
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
- 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
- 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
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
- 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