Baseline predictors of mortality in non-idiopathic pulmonary fibrosis interstitial lung disease - A retrospective cohort study at a tertiary centre in Malaysia

This retrospective cohort study of non-idiopathic pulmonary fibrosis interstitial lung disease patients in Malaysia identifies baseline forced vital capacity, age, specific disease subtypes, and notably ethnicity as independent predictors of mortality, with Chinese and Indian patients facing significantly higher risks compared to Malays.

The Gist

Imagine your lungs are like a complex, bustling city. In a healthy city, the airways are wide, clean streets, and the buildings (alveoli) are flexible and ready to exchange oxygen.

Interstitial Lung Disease (ILD) is like a slow, creeping fog that settles over this city. It causes the streets to get clogged with scar tissue (fibrosis) and the buildings to become stiff. While there is a famous, well-studied version of this fog called IPF (Idiopathic Pulmonary Fibrosis), this paper focuses on the "other" types of fog—Non-IPF ILD. These are caused by different things: autoimmune diseases (where the body attacks itself), breathing in bad dust, or unknown reasons.

Until now, doctors have had a very good map for predicting the fate of the IPF fog, but the map for the "other" fogs has been blurry. This study, conducted at a major hospital in Malaysia, tried to draw a clearer map for these other types.

Here is the story of what they found, explained simply:

1. The Players in the Study

The researchers looked at 229 patients over 13 years. It's important to note the mix of people:

• Gender: There were many more women than men (3 women for every 1 man).
• Ethnicity: Malaysia is a melting pot. The group included Malays, Chinese, and Indians.
• The "Fog" Types: The patients had different causes for their lung scarring, including autoimmune diseases (CTD), unknown causes (IIP), breathing in allergens (Hypersensitivity Pneumonitis or HP), and rare conditions.

2. The "Weather Report" for Survival

The team wanted to know: Who is most likely to survive, and who is at higher risk? They looked at the "weather conditions" at the time of diagnosis.

The Big Three Predictors of Risk:

1. Age: Being older (over 50) was like driving a car with worn-out brakes. It made the journey riskier.
2. Lung Capacity (FVC): Imagine your lungs are a balloon. If the balloon can only be inflated to less than half its normal size (less than 50% capacity), the risk of a bad outcome triples. This was a stronger warning sign than in Western studies, suggesting that in this Asian population, the "danger zone" for lung size is lower.
3. Ethnicity (The Surprise Finding): This was the most unique discovery. The study found that Chinese and Indian patients had a significantly higher risk of mortality compared to Malay patients, even when they had the same age, lung capacity, and disease type.
   • Analogy: It's like two cars with the same engine and the same driver, but one car has a hidden, invisible flaw in its chassis that makes it more prone to accidents. The researchers suspect this "flaw" could be genetic, cultural habits, or different environmental exposures, but they aren't sure yet.

3. The "Fog" Types: Who is the Worst Off?

Not all fogs are created equal. The study ranked the different types of ILD by how quickly they moved:

• The Slowest (Best Prognosis): Pulmonary Sarcoidosis and Connective Tissue Disease (CTD). These were like a light mist that often clears up or stays manageable.
• The Fastest (Worst Prognosis): Hypersensitivity Pneumonitis (HP). This was the "storm" of the group. Patients with this condition had the shortest survival time (about 6 years on average), which is surprisingly close to the prognosis of the dreaded IPF.
• The Middle Ground: Idiopathic Interstitial Pneumonia (IIP) and "Unclassifiable" cases fell in the middle.

4. Why Does This Matter?

Think of this study as a compass for doctors in Malaysia and similar regions.

• Before: Doctors might have treated all "Non-IPF" patients the same, using maps designed for Western populations.
• Now: They know that in this region, a patient's ethnicity and lung capacity are critical clues. If a Chinese or Indian patient walks in with a lung capacity under 50%, the doctor knows to sound the alarm immediately.

The Bottom Line

The researchers concluded that while we have good tools for some lung diseases, we need to stop using a "one-size-fits-all" map.

• The Mystery: Why do Chinese and Indian patients in this study have a harder time? The paper suggests it might be a mix of genes (the blueprint of the house), culture (how people live and cook), or environment (what they breathe in).
• The Call to Action: We need more studies to solve this mystery. Until then, doctors should treat patients based on their specific background and lung function, not just the name of their disease.

In short: This study tells us that in the diverse landscape of Malaysia, the "fog" of lung disease behaves differently depending on who you are and how much air your lungs can hold. Recognizing these differences is the first step to saving more lives.

Technical Summary

1. Problem Statement

Interstitial Lung Diseases (ILDs) other than Idiopathic Pulmonary Fibrosis (IPF) constitute a heterogeneous group of disorders with varying prognoses. While the GAP model (Gender, Age, Physiology) is well-validated for predicting mortality in IPF, its applicability to non-IPF ILD is inconsistent due to the diverse etiologies involved (e.g., connective tissue diseases, hypersensitivity pneumonitis, sarcoidosis). Furthermore, there is a significant lack of data regarding baseline mortality predictors for non-IPF ILD in Asian and multi-ethnic populations, particularly in Southeast Asia. Existing models often rely on Caucasian cohorts, potentially overlooking regional variations in disease phenotype, genetic background, and environmental exposures.

2. Methodology

• Study Design: Retrospective cohort study.
• Setting: Universiti Malaya Medical Centre (UMMC), a tertiary referral center in Kuala Lumpur, Malaysia.
• Timeframe: January 1, 2010, to May 31, 2023.
• Population:
  • Inclusion: Adult patients (≥18 years) diagnosed with non-IPF ILD.
  • Exclusion: Patients lacking baseline High-Resolution Computed Tomography (HRCT) or Respiratory Function Test (RFT) data; pulmonary fibrosis not due to ILD; non-pulmonary sarcoidosis.
  • Final Cohort: 229 patients (after excluding 114 patients due to missing baseline lung function data).
• Data Collection:
  • Demographics (age, gender, ethnicity), clinical history (smoking, comorbidities), and baseline investigations (HRCT, RFT, autoantibodies, biopsies).
  • Diagnostic Confirmation: All cases were cross-verified by experienced pulmonologists and a thoracic radiologist against International Guidelines.
• Statistical Analysis:
  • Survival Analysis: Kaplan-Meier method with log-rank tests to compare survival across subtypes.
  • Predictor Identification: Univariate and Multivariate Cox proportional hazard regression models. Variables with $p < 0.25$ in univariate analysis were entered into the multivariate model.
  • Significance: $p < 0.05$ (two-sided).

3. Key Contributions

• Regional Validation: Provides the first comprehensive analysis of baseline mortality predictors for non-IPF ILD specifically within a multi-ethnic Malaysian cohort (Malay, Chinese, Indian).
• Ethnicity as a Prognostic Factor: Identifies ethnicity as an independent predictor of mortality, a variable often underrepresented in global ILD prognostic models.
• Physiological Thresholds: Challenges the applicability of Western-derived FVC thresholds for Asian populations, suggesting different risk stratification cut-offs.
• Subtype-Specific Prognosis: Offers granular survival data for specific non-IPF subtypes (e.g., Hypersensitivity Pneumonitis vs. Connective Tissue Disease-ILD) in this demographic.

4. Key Results

• Demographics:
  • Mean age: 60 ± 15 years.
  • Gender: Female-to-Male ratio of 3:1.
  • Ethnicity: Indians (47.6%), Chinese (31.9%), Malays (20.5%).
  • Most common subtype: Connective Tissue Disease-ILD (CTD-ILD, n=117).
• Baseline Characteristics:
  • Mean baseline Forced Vital Capacity (FVC): 53.3 ± 21% predicted.
  • 50.7% of patients had an FVC <50% predicted.
• Multivariate Predictors of Mortality:
  The following factors were independently associated with increased mortality risk:
  1. Age ≥50 years: Hazard Ratio (HR) 3.23 (95% CI 1.11–9.43).
  2. FVC <50% predicted: HR 3.65 (95% CI 1.65–8.06).
  3. Ethnicity:
     • Chinese: HR 9.86 (95% CI 1.27–76.89) compared to Malays.
     • Indian: HR 8.59 (95% CI 1.14–64.69) compared to Malays.
  4. ILD Subtypes:
     • Idiopathic Interstitial Pneumonia (IIP): HR 2.39 compared to CTD-ILD.
     • Hypersensitivity Pneumonitis (HP): Showed a trend toward higher mortality (HR 2.10), though not statistically significant in the final multivariate model ($p=0.185$), but showed the poorest survival in Kaplan-Meier analysis.
• Survival Outcomes:
  • Kaplan-Meier Analysis: Significant differences in survival across subtypes ($p=0.048$).
  • Poorest Prognosis: Hypersensitivity Pneumonitis (HP) had the shortest mean survival (6.1 years), approaching the prognosis of IPF.
  • Best Prognosis: Pulmonary Sarcoidosis and CTD-ILD demonstrated the most favorable survival outcomes.

5. Significance and Implications

• Clinical Management: The study suggests that FVC <50% is a critical threshold for high mortality risk in this Asian cohort, which is lower than the ~70% threshold often cited in Caucasian studies. This implies that risk stratification tools must be population-specific.
• Ethnic Disparities: The finding that Chinese and Indian patients have significantly higher mortality risks than Malay patients (even after adjusting for age, lung function, and comorbidities) highlights the need to investigate underlying mechanisms, such as:
  • Genetic variations.
  • Cultural differences in environmental exposures (e.g., agricultural practices, indoor air quality).
  • Socioeconomic factors (though not explicitly measured in this study).
• Treatment Strategy: Early identification of high-risk features (older age, low FVC, specific ethnicities, and HP/IIP subtypes) allows for timely intervention, including:
  • Initiation of antifibrotic therapy.
  • Aggressive immunosuppression.
  • Referral for lung transplantation evaluation.
• Future Research: The authors emphasize the need for large, prospective, multi-center studies to validate these findings and to explore the biological and environmental drivers behind the observed ethnic disparities.

Limitations Noted:

• Retrospective design with potential selection bias (exclusion of patients without baseline RFTs may have removed the most severe cases).
• Single-center data limits generalizability to the entire Malaysian population.
• Lack of socioeconomic data and limited Diffusing Capacity of the Lungs for Carbon Monoxide (DLCO) data.