Abstract

 Introduction: Interstitial lung diseases are a group of diffuse parenchymal lung disorders associated with substantial morbidity and mortality and pose diagnostic and therapeutic challenges to the clinician. Diagnosis of ILD is by multidisciplinary discussion (MDD) between clinician, radiologist and pathologist. Risk prediction is challenging in ILDs because of heterogeneity in disease-specific and patient-specific variables. Studies assessing factors associated with mortality in ILDs are scarce in our setting. Prospective disease registries can provide better estimates of incidence and prevalence as well as insights to etiology, associated risks, natural history, and outcomes of a disease. Data regarding the use of composite prediction models like Composite physiologic index and ILD Gap index are limited.

Aim of study 1.To compare the adverse outcome, as defined by>10% decline in FVC and mortality  at 6 months in patients with Idiopathic pulmonary fibrosis (IPF) and other non IPF interstitial  lung diseases diagnosed by MDD, at Department of Pulmonary medicine, MCH, Trivandrum over a period of two years. Secondary objectives were to determine factors affecting adverse outcomes in interstitial lung diseases and to evaluate the prognostic value of composite physiologic index(CPI) and ILD - GAP index in interstitial lung diseases.

Study design: Prospective Cohort study.

Study setting: Department of Pulmonary Medicine, Government Medical College Trivandrum. Study period: Two years.

Study population: Patients with multidisciplinary diagnosis of ILD, attending Department of Pulmonary Medicine, Government Medical College Trivandrum, Inclusion criteria: All patients diagnosed as ILD patients, who give consent to participate in the study. Exclusion criteria: ILD Patients with Lung Cancer or Pulmonary Tuberculosis. Data collection A prospective cohort study over a period of two years conducted at Pulmonary medicine, Department, Medical College, Thiruvananthapuram. 164 consecutive patients with multidisciplinary diagnosis of interstitial lung disease were included in the study. Detailed history, spirometry, SPO2, DLCO, HRCT, 6 minute walk test, ECG,2D ECHO were done and recorded in duly filled proforma. ANA profile, serum angiotensin converting enzyme, serum calcium, 24 hour urinary calcium were estimated wherever it was indicated. Diagnosis of IPF was done after excluding the known causes and the HRCT findings suggestive of UIP pattern based on the current guidelines of the American Thoracic Society/European Respiratory Society CPI was calculated from spirometry and DLCO. ILD GAP index was also calculated. Patients were given appropriate therapy as per the clinical subtypes. Patients were followed up with clinical assessment and spirometry, and DLCO at 6 months. Outcome variables assessed were death and FVC decline ≥ 10%/ at 6   months.

Institutional ethical committee clearance was obtained before data collection. Statitical Analysis. Data were entered in Microsoft Excel and analyzed using Epi Info version 7. For descriptive statistics, quantitative variables were described by mean and standard deviation. Qualitative variables were described by percentage distribution. For inferential statistics between groups, comparison of qualitative variables were analysed by chi-square test and quantitative variables were compared by student t test. P value of less than 0.05 was considered as level of significance.

Survival pattern was assessed by Kaplan-meir survival plot.

Results: Out of the 164 patients studied, 26.2% were idiopathic pulmonary fibrosis (IPF) and 73.78% were non-IPF.15.2% died at 6 months follow up, of which 72% were IPF. 51.2% had a fall in FVC ≥ 10% at 6 months. In bivariate analysis, factors associated with mortality in interstitial lung diseases are: age > 60, male gender, BMI < 18.5, smoking, presence of pulmonary hypertension, mean saturation< 90%, % predicted FVC < 50%, % predicted DLCO < 40%, 6 Minute walk distance < 250m,at diagnosis, UIP pattern in HRCT, CPI score > 50 and ILD- GAP index > 4. On multivariate analysis using logistic regression, factors associated with mortality were age > 60 years and IPF group.  Similar Factors were associated with decline in FVC more than 10%  at 6 months in bivariate analysis, whereas On multivariate analysis are history of smoking and initial % predicted DLCO <40% were significant. ILD Gap index is a better predictor of mortality than Composite physiologic index in interstitial lung diseases. (AUROC 0.912 vs 0.856 for CPI).

Conclusion: The factors associated with mortality in ILD were age >60 years, type of ILD as idiopathic pulmonary fibrosis and decline in FVC ≥ 10% at 6 month. and FVC < 50% at baseline. The availability of reliable prediction models like composite physiologic index (CPI) and ILD Gap index can help in prognostication and making clinical decisions. ILD Gap index was a better predictor of mortality than composite physiologic index.   

Keywords: Interstitial lung diseases, adverse outcomes, mortality, FVC decline, composite physiologic index, ILD Gap index.

Dr Sreekala C

Navaneetham, APRA 307, Ajantha Pulli Lane,

Pettah PO, Chackai, Trivandrum 695024

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