What is interstitial lung disease (ILD) and how is it managed?

Interstitial Lung Disease: Definition and Management

Interstitial lung diseases (ILDs) are a diverse group of disorders characterized by inflammation and/or fibrosis of the lung parenchyma that cause progressive dyspnea, frequently resulting in end-stage respiratory failure and significant mortality. 1

Definition and Epidemiology

• ILDs comprise a heterogeneous group of chronic lung disorders affecting the interstitium, alveolar spaces, and sometimes the bronchial system 2
• The prevalence ranges between 72.1 and 164.2 cases per 100,000 Europeans, with approximately 650,000 people affected in the US 3, 1
• ILDs cause approximately 25,000 to 30,000 deaths per year in the US 1
• The most common forms include:
  • Idiopathic pulmonary fibrosis (IPF) - approximately one-third of all cases 1
  • Connective tissue disease-associated ILD (CTD-ILD) - approximately 25% of cases 1
  • Hypersensitivity pneumonitis - approximately 15% of cases 1

Pathophysiology

• ILDs involve inflammation and scarring (fibrosis) of the interstitium, obliterating alveoli and capillary units 4
• Progressive pulmonary fibrosis (PPF) causes irreversible lung damage, significant morbidity, and increased mortality 3
• The scarring produces restrictive lung impairment while destruction of alveoli, interstitium, and capillaries results in severe gas exchange abnormalities 4

Clinical Presentation

• Early symptoms are often nonspecific and can be overlooked:
  • Progressive dyspnea on exertion (primary symptom) 1, 4
  • Dry cough (approximately 30% of patients) 1
  • Fatigue 3
• Physical examination may reveal:
  • Bibasilar crackles (rales) on auscultation 4
  • Digital clubbing (in some cases) 5
• Symptoms may be absent in sedentary patients or masked by other organ involvement or comorbidities 3

Diagnostic Approach

• High-resolution computed tomography (HRCT) is essential for diagnosis:
  • Approximately 91% sensitive and 71% specific for diagnosing ILD subtypes 1
  • Can identify specific patterns (UIP, NSIP, etc.) 3
• Pulmonary function tests (PFTs) are crucial for assessment:
  • Typically show restrictive pattern with reduced FVC and DLCO 3, 1
  • A 5% decline in FVC over 12 months is associated with approximately 2-fold increase in mortality 1
• Multidisciplinary discussion (MDD) involving pulmonologists, radiologists, and pathologists is essential for accurate diagnosis 3
• Surgical lung biopsy may be required when HRCT findings are inconclusive 3

Management Approach

General Principles

• Treatment should be based on the specific ILD diagnosis, disease behavior, and risk factors 3, 6
• Multidisciplinary team collaboration is essential, particularly for CTD-ILD 3
• Early recognition and intervention are critical to slow irreversible lung function loss 3

Specific Treatments

• For idiopathic pulmonary fibrosis (IPF):

  • Antifibrotic therapy with nintedanib or pirfenidone is first-line treatment 7, 1
  • These medications slow annual FVC decline by approximately 44% to 57% 1
  • Pirfenidone demonstrated reduced mean decline in FVC compared to placebo (treatment difference 193 mL) at 52 weeks 7

• For CTD-ILD:

  • Immunomodulatory therapy (tocilizumab, rituximab, mycophenolate mofetil) may slow decline or improve FVC 1, 8
  • Antifibrotic medications may be beneficial for progressive fibrosing phenotypes 8
  • Systematic monitoring with short-term PFTs and repeat HRCT is recommended to determine progression rate 3, 6

• For smoking-related ILD:

  • Smoking cessation is the single most effective intervention 6
  • Combination of pharmacotherapy and behavioral support increases cessation success 6

Supportive Care

• Oxygen therapy for patients who desaturate below 88% on exertion improves symptoms and quality of life 1
• Structured exercise therapy reduces symptoms and improves 6-minute walk test distance 1
• Pulmonary rehabilitation is beneficial for symptom management 1
• Vaccinations (influenza, pneumococcal) to reduce risk of respiratory infections 6

Advanced Disease Management

• Lung transplantation should be considered for end-stage ILD:
  • Improves symptoms and resolves respiratory failure 1
  • Median survival after transplant is 5.2 to 6.7 years compared to less than 2 years without transplant 1
• For ILD-associated pulmonary hypertension (occurs in up to 85% of end-stage fibrotic ILD):
  • Inhaled treprostinil improves walking distance and respiratory symptoms 1

Monitoring and Follow-up

• Regular assessment of symptoms, pulmonary function, and imaging is essential 3, 6
• Short-term PFTs (within 3 months) and repeat HRCT (within 6 months) should be considered to determine progression rate 6
• A decline in FVC ≥5% or DLCO ≥10% over 6-12 months indicates disease progression 1

Common Pitfalls to Avoid

• Delayed diagnosis due to nonspecific symptoms being attributed to other conditions 4
• Treating radiographic infiltrates as atypical pneumonias that fail to respond to antimicrobial therapy 4
• Failing to recognize disease progression due to infrequent monitoring 6
• Delaying treatment while focusing solely on diagnostic precision rather than initiating appropriate therapy 3