What is the treatment for a patient diagnosed with hypersensitivity pneumonitis?

Treatment of Hypersensitivity Pneumonitis

Complete and immediate antigen avoidance is the single most critical intervention to alter disease trajectory and mortality in hypersensitivity pneumonitis, and must be prioritized above all other treatments. 1, 2

Initial Management: Antigen Identification and Avoidance

The cornerstone of HP management is identifying and eliminating exposure to the inciting antigen. This requires:

• Comprehensive exposure history focusing on occupational, household, and recreational exposures including birds, molds, humidifiers, hot tubs, metalworking fluids, and indoor water damage 3
• Environmental assessment by occupational medicine specialists and certified environmental hygienists when the exposure source is unclear or occupational 3
• Immediate removal from the suspected environment within days if the antigen source cannot be remediated 1

Critical caveat: Patients with unidentified inciting antigens have significantly worse survival (HR 2.08; 95% CI 1.02-4.24) compared to those with identified exposures, making thorough exposure assessment essential 1, 2

Phenotype-Based Treatment Approach

Non-Fibrotic HP

For patients without radiological or histopathological evidence of fibrosis:

• Antigen avoidance alone is often sufficient, with clinical improvement typically occurring within 2 weeks to 3.4 months 1, 2
• Corticosteroids (prednisone 1-2 mg/kg/day tapered over 4-8 weeks) are recommended only for severe disease or respiratory failure 1, 2, 4
• Expected outcomes: Lung function improvement averages 3.4 ± 2.4 months after antigen cessation, with corticosteroids reversing lung function decline from -0.35% monthly to +0.84% monthly (P < 0.01) 1

Fibrotic HP

For patients with radiological or histopathological evidence of fibrosis:

• Antigen avoidance remains essential despite limited response, as clinical improvement is associated with decreased mortality (HR 0.18; 95% CI 0.04-0.77) 1, 2
• Higher-dose corticosteroids may be needed for longer periods, though response is often limited 1, 4
• Steroid-sparing immunosuppressants (mycophenolate mofetil 500-1000 mg/m² body surface area or azathioprine) should be considered for patients requiring prolonged therapy, as they alter the slope of FVC decline and improve DLCO 1
• Antifibrotic therapy (nintedanib) is FDA-approved for progressive fibrotic HP and should be considered for patients with progressive phenotype 5

Monitoring Response to Treatment

• Pulmonary function testing (FVC%, DLCO%) should be performed regularly to objectively document response 2
• Clinical improvement with antigen avoidance has 51% sensitivity and 81% specificity for HP diagnosis in non-fibrotic disease 1
• Lack of improvement does not rule out HP, especially in fibrotic disease where progression may occur despite all interventions 1, 2, 4

Special Exposure-Specific Management

Hot Tub Lung (Mycobacterial HP)

• Complete avoidance of indoor hot tub use; move outdoors or remove entirely 1, 2
• Antimycobacterial therapy for 3-6 months if symptoms persist after antigen avoidance 2

Marijuana-Related HP

• Complete cessation of marijuana smoking is mandatory 4
• Environmental assessment to identify mold or chemical contaminants in the marijuana 4

Occupational HP

• Workplace removal with assistance from occupational medicine specialists 3
• Workers' compensation evaluation when applicable 3

Critical Pitfalls to Avoid

• Never escalate immunosuppression without ensuring complete antigen avoidance first, as continued exposure negates treatment benefits and increases mortality 1, 4
• Do not assume lack of improvement rules out HP, particularly in fibrotic disease where progression is common despite treatment 1, 2, 4
• Do not rely solely on clinical improvement with medical therapy to confirm or rule out HP diagnosis 2, 4
• Do not overlook the need for steroid-sparing agents in patients requiring prolonged corticosteroid therapy 1, 4

Long-Term Management

• Continued surveillance for exposure at every visit with patient education focused on antigen avoidance 2
• Regular maintenance of potential antigen sources (humidifiers, HVAC systems) according to manufacturer recommendations 3
• Multidisciplinary discussion involving pulmonologists, radiologists, and pathologists for complex cases 3