Interstitial lung diseases (ILDs) are a group of lung parenchymal diseases characterized by a variable degree of inflammation that involves the alveolar walls, interstitium, and terminal airspaces [1]. The clinical and radiological pattern in this disease may have similar presentations, yet its etiology, histopathology, and progression are completely different. Therefore, identification of clinical, radiological, and etiological patterns is important for appropriate management and outcomes [2]. There is a growing pattern of increase in diagnosis of ILDs, which could be because of increased awareness and improved diagnostic modalities such as the use of high-resolution computed tomography (HRCT) [3]. The pattern of ILDs in low- and middle-income countries such as India still remains limited. The global epidemiological data show that the prevalence of ILD ranges from 13% to 20% per 100,000 population. Regional studies from India report variable presentation in frequency because of differences in environmental exposures, occupational hazards, and genetic predisposition [4]. Large multicentric registries in India, such as the ILD India registry, have found significant differences in the epidemiology of ILD as compared to the western population [5]. In western countries, the predominant pattern of ILD was idiopathic pulmonary fibrosis (IPF), as in India, it has been found that hypersensitivity pneumonitis (HP) is the predominantly prevalent condition, followed by connective tissue disease-associated ILD (CTD-ILD) [6]. The increased incidence of HP in India could be due to the use of biomass fuel, organic antigens, and environmental pollution [7]. Compounding the problem is the late presentation in cases, and the limited availability of diagnostic facilities results in underdiagnosis and misclassification of ILDs [8]. The common clinical presentation of ILD patients is progressive exertional dyspnea and dry cough. Clinical examination of such patients often reveals existing fine respiratory crackles, and clubbing may also be present in some cases [9]. Pulmonary function test (PFT) in such cases shows a restrictive ventilatory pattern and reduced diffusion capacity for carbon monoxide (DLCO), which indicates impaired alveolar-capillary gas exchange [10]. Since many cases show non-specific symptoms, which result in delayed diagnosis or patients being treated for bronchitis, they are sometimes treated for tuberculosis before ILD is diagnosed [11]. Radiological evaluation by HRCT remains the gold standard in ILD diagnosis because of its ability to provide fine visual details of parenchymal abnormalities and help in differentiation from interstitial pneumonia (UIP), non-specific interstitial pneumonia (NSIP), and organizing pneumonia (OP) [12]. In most cases, the use of HRCT along with clinical and serological tests is enough for diagnosis without the need for lung biopsy [13]. Despite these obvious advantages, HRCT remains underutilized in several parts of India due to cost and limited availability [14]. The etiology of ILD encompasses a broad range of causes that include autoimmune diseases, occupational and environmental exposures, drug reactions, infections, and idiopathic causes [15]. Identifying these etiological factors is vital as certain forms, such as HP or drug-induced ILDs, may be reversible if they are recognised early and the offending exposure removed [16]. On the other hand, fibrotic forms (IPF) have an inexorable progressive course that often leads to respiratory failure despite therapy [17]. With this background, the current study aimed to analyse the clinical presentation, radiological pattern, and etiological distribution of ILDs in a tertiary care hospital setting. This regional evaluation will help in understanding the local burden present to highlight the challenges associated with diagnosis, as well as the use of a more standardized approach towards ILD diagnosis and management in the Indian population.

This cross-sectional prospective observational study was conducted in the Department of Pulmonary Medicine, Govt Medical College and Hospital, Jangaon, Telangana. Institutional Ethical approval was obtained for the study after explaining the nature of the study in the vernacular language. Written consent was obtained from all the participants of the study after explaining the nature of the study in the vernacular language. Inclusion criteria 1. Adults aged 18 years and above 2. Chronic respiratory symptoms like dyspnea and dry cough. 3. Radiological imaging suggestive of diffuse parenchymal lung disease 4. Referred for evaluation of ILD 5. Signed the written consent Exclusion criteria 1. Acute cardiorespiratory instability 2. Patients in whom investigations were not carried out 3. Pregnancy 4. Refused to sign informed consent 5. Patients on definitive antifibrotic therapy for more than 3 months 6. Pulmonary tuberculosis 7. Acute respiratory infections The sample size obtained for the study during the period of study was n=45. The method of sample collection followed in this study was a convenience sampling method. After selection of the case based on the inclusion and exclusion criteria, a standardized case record form was used to record demographic data, smoking history, occupational and environmental exposures, existing comorbidities, symptom duration, and systemic features suggestive of connective tissue diseases. Complete physical examination with auscultatory findings (bibasilar crackles), clubbing, and other signs of systemic diseases were recorded. Pulmonary function test (PFT): All the patients underwent a pulmonary function test as per American Thoracic Society (ATS) and European Respiratory Society (ERS) ATS/ERS guidelines. The results were categorized as restrictive, obstructive, or mixed patterns. Diffusing capacity for carbon monoxide (DLCO) was determined if possible. Routine laboratory tests were done: complete blood count, ESR/CRP, renal and liver function tests. Targeted serological screening for connective tissue disease (ANA, rheumatoid factor, anti-CCP, ENA panel) was carried out if clinically indicated. Where applicable, testing for hypersensitivity pneumonitis (precipitins) and precipitins to suspected antigens was undertaken. All patients received chest high-resolution computed tomography (HRCT) (1-1.5 mm slices) using a standard protocol. HRCT images were reviewed independently by two experienced thoracic radiologists who were blinded to the clinical data. Radiological patterns were classified as usual interstitial pneumonia (UIP), probable UIP, nonspecific interstitial pneumonia (NSIP), organizing pneumonia (OP), hypersensitivity pneumonitis (HP) pattern, or indeterminate according to the established ATS/ERS/Fleischner criteria. Flexible bronchoscopy with bronchoalveolar lavage (BAL) was done as clinically indicated. BAL cellular analysis and microbiology (including AFB staining/culture and fungi) were used to rule out infection. Each case was classified etiologically (idiopathic interstitial pneumonia, CTD-ILD, HP, drug-related, occupational, others) after the integration of clinical, serological, BAL, histopathological, and HRCT data. Statistical analysis: All the available data were entered in an MS Excel spreadsheet and analyzed by SPSS version 26 in Windows format. The continuous variables were represented as mean, standard deviation, or median (IQR), frequency, and percentages. The categorical variables were calculated by the Mann-Whitney U test for continuous variables and χ² analysis. The values of (p<0.05) were considered significant.

The study involved a total of n=45 patients who were diagnosed with interstitial lung disease (ILD). The mean age of the participants was 62.4 ± 10.8 years. The largest number of those (62.2%) were in the age group of 50-70 years, which is due to the higher prevalence of ILD in middle-aged and elderly people. Males (57.8%) marginally outnumbered females (42.2%), in line with the worldwide epidemiological pattern of fibrotic ILDs such as idiopathic pulmonary fibrosis (IPF). The assessment of risk factors and exposure is presented in Table 1. A critical analysis of the table showed that this cohort included 44.4% of patients who never smoked 40% of them were ex-smokers, and 15.6% were current smokers. This showed that the association between smoking and incidence of ILD subtypes, especially of IPF and desquamative interstitial pneumonia, was significant. Occupational exposure to dust or chemical agents was found to be present in 35.6% of cases, and biomass fuel exposure was present in 26.7% of cases, which highlights the role of environmental risk factors in this cohort. About 20% of the cases had exposure to birds on farms, which leads to hypercreativity pneumonitis. The overall duration of symptoms ranged from (IQR 9–36 months) and a median of 18 months, which indicates a chronic course before diagnosis. Clinical examination showed the presence of clubbing in 33.3%, and bibasilar crackles were heard in 88.9% of patients. Evaluation of signs and symptoms of the cohort is given in Table 2. The universal symptom in the cohort was dyspnea (100%), which was MRC grade ≥2. A dry cough was present in 91.1% of cases, and systemic features such as fatigue were common in 71.1% cases, weight loss in 40% and arthralgia and arthritis were in 31.1% cases. These signs indicate that multisystem involvement occurs due to ILDs. Patients with concurrent involvement of connective tissue disease associated with ILD (CTD-ILD) were found to have Raynaud's phenomenon in 13.3% cases and skin rash in 11.1% of cases. Pulmonary function testing (PFT) was comparable with parenchymal fibrosis in 77.8% of patients with a restrictive ventilatory defect (Table 3). Isolated reduction in DLCO was observed in 15.6% of the patients, and a mixed obstructive/restrictive pattern was rare (4.4%). Only one patient (2.2%) had normal spirometry. Of those with a measurable DLCO (n=40), the impairment was mild (30%), moderate (45%), and severe (25%), indicating functional impairment of significant magnitude in the majority of cases. High-resolution computed tomography (HRCT) patterns revealed that Usual Interstitial Pneumonia (UIP) was the leading radiological subtype, which was identified in 26.7% of patients, followed by the probable UIP (22.2%) and Non-specific interstitial Pneumonia (NSIP) pattern in 20% of patients (Table 4). Hypersensitivity pneumonitis (HP) and organizing pneumonia (OP) patterns were observed in 15.6% and 8.9% cases, respectively, while 6.7% were unclassifiable because of overlapping or nonspecific features. After multidisciplinary discussion (MDD), idiopathic interstitial pneumonias (IIPs) were the largest etiological group, accounting for 53.3% of cases (Table 5). Among them, Idiopathic Pulmonary Fibrosis (IPF) represented 40% of patients, idiopathic NSIP represented 8.9% and cryptogenic organizing pneumonia 4.4%. Connective tissue disease-associated ILD (CTD-ILD) 24.4% most commonly rheumatoid arthritis-associated ILD 11.1% followed by systemic sclerosis-associated ILD 6.7% and other CTD-ILDs 6.7% e.g., Sjorgren's syndrome, inflammatory myositis, and mixed connective tissue disease - ILDs. Hypersensitivity pneumonitis represented 15.6% and occupational/environmental ILD and Unclassifiable ILD, respectively, 4.4% and 2.2%. Overall, the results show that idiopathic pulmonary fibrosis and CTD-related ILDs are the most common etiology of ILD in this series, with restrictive physiology and fibrotic HRCT patterns being the most common clinical and radiological features. Table 1: Baseline Demographic and Clinical Characteristics of the Study Population (N=45) Characteristic Category Number (n) Percentage (%) Age (Years) Mean SD 62.4 ± 10.8 <50 7 15.6 50-70 28 62.2 >70 10 22.2 Sex Male 26 57.8 Female 19 42.2 Smoking History Never Smoker 20 44.4 Ex-Smoker 18 40 Current Smoker 7 15.6 Occupational Exposure Yes 16 35.6 Biomass Exposure Yes 12 26.7 Bird/Farm Exposure Yes 9 20.0 Symptom Duration (Months) Median (IQR) 18 (9-36) Presence of Clubbing Yes 15 33.3 Auscultatory Crackles Yes 40 88.9 Table 2: Presenting Symptoms and Clinical Signs (N=45) Symptom/Sign Number (n) Percentage (%) Dyspnea (MRC Grade 22) 45 100.0 Dry Cough 41 91.1 Fatigue 32 71.1 Weight Loss (>5% body weight) 18 40.0 Arthralgia/Arthritis 14 31.1 Raynaud's Phenomenon 6 13.3 Skin Rash 5 11.1 Table 3: Pulmonary Function Test Patterns (N=45) PFT pattern Number (n) Percentage (%) Restrictive Defect 35 77.8 Isolated DLCO Reduction* 7 15.6 Mixed Obstructive & Restrictive 2 4.4 Normal 1 2.2 DLCO Severity (n=40) Mild (260% predicted) 12 30.0 Moderate (40-59% predicted) 18 45.0 Severe (<40% predicted) 10 25.0 *With preserved lung volumes. DLCO: Diffusing Capacity for Carbon Monoxide. Table 4: High-Resolution CT (HRCT) Thorax Patterns (N=45) HRCT pattern Number (n) Percentage (%) Usual Interstitial Pneumonia (UIP) 12 26.7 Probable UIP 10 22.2 Nonspecific Interstitial Pneumonia (NSIP) 9 20.0 Hypersensitivity Pneumonitis (HP) Pattern 7 15.6 Organizing Pneumonia (OP) Pattern 4 8.9 Unclassifiable / Indeterminate 3 6.7 Table 5: Final Etiological Classification after Multidisciplinary Discussion (MDD) (N=45) Etiological Category Specific Diagnosis Number (n) Percentage (%) Idiopathic Interstitial Pneumonias 24 53.3 Idiopathic Pulmonary Fibrosis (IPF) 18 40.0 idiopathic NSIP 4 8.9 Cryptogenic Organizing Pneumonia 2 4.4 Connective Tissue Disease-Associated ILD (CTD-ILD) 11 24.4 Rheumatoid Arthritis-ILD 5 11.1 Systemic Sclerosis-ILO 3 6.7 Other CTD-ILD* 3 6.7 Hypersensitivity Pneumonitis (HP) 7 15.6 Occupational/Environmental ILD 2 4.4 Unclassifiable ILD 1 2.2 *Includes Sjogren's syndrome, inflammatory myositis, and mixed connective tissue disease.

The current study was done to analyze the clinical, radiological, and etiological spectrum of interstitial lung disease in patients presenting to our tertiary care hospital. A total of n=45 cases were analyzed during the duration of the study. The overall findings of this study were consistent with prior global and regional studies, which showed that ILD commonly affects older adults with a higher prevalence among males and individuals exposed to occupational and environmental risk factors [1, 3, 10]. The mean age of the cohort was 62.4 years, which is similar to the results shown by other studies in this field. Raghu et al. [15] and Travis et al. [1] in their respective study found that idiopathic pulmonary fibrosis is one of the most prevalent idiopathic interstitial pneumonias, which typically manifests after the sixth decade of life. The male predominance as observed in the result of this study was also shown in other studies, which reported higher prevalence in males due to existing risk factors such as smoking and occupational exposures common in males [3, 12] We noticed existing environmental occupational risk factors in our patients. Approximately 35.65% of the cases of this study had exposure to dust or chemical agents, while 26.7% had chronic exposure to biomass fuel. This pattern is consistent with findings reported from other Indian as well as foreign studies which showed environmental factors are the significant burden for the ILD [13, 14] An exposure to bird or farm was exsiting in 205 of cases which is an important etiological clue for hypersensitivity pneumonitis (HP) which was also reported by Selman et al. [18] in their study. The important clinical features in this study showed the universal existence of dyspnea, followed by 91.1% having a dry cough. These typical findings are characteristics of ILD, and it has been shown by King et al. [19] in their study. There were existing systemic symptoms such as fatigue, arthralgia, and weight loss in one third of cases, which shows the overlapping features between idiopathic and connective tissue disease-related ILDs (CTD-ILDs). The physical findings in patients, such as the presence of clubbing (33.3%) and bibasilar crackles (88.9%), showed the diagnosis of chronic fibrosing interstitial disease. Patients were subjected to a Pulmonary function test (PFT), the results of which showed a predominant restrictive pattern of lung involvement (77.8%) of cases with varying degrees of diffusion impairment, and aligning with common findings in ILD. The estimation of DLCO reduction in the cases with existing (mild in 30%, moderate in 45%, severe in 25%) reductions indicates significant alveolar-capillary membrane dysfunction related to disease severity and extent of fibrosis [5, 20]. The most important role in the diagnosis of ILDs is played by HRCT findings, which require classification of the disease as well. The Usual Interstitial Pneumonia (UIP) pattern was commonly found in 26.75% of cases, followed by probable UIP (22.2%) and Nonspecific Interstitial Pneumonia (NSIP) (20%) of cases. These findings are concurrent with the ATS/ERS classification and studies from Middle Eastern cohorts, where UIP and NSIP are the dominant radiologic patterns on HRCT (10,14). The presence of HP (15.6%) and organizing pneumonia (8.9%) showed the heterogeneity of ILDs, which highlights the role of integrating clinical, radiological, and exposure analysis for accurate diagnosis. Based on multidisciplinary analysis, we found Idiopathic interstitial pneumonias (IIPs) were the frequent etiologic group (53.3%), and IPF constituted 40% of total ILDs. This distribution is consistent with studies from the ILD India Registry and the Middle East, where IPF is among the leading subtypes (14, 19). CTD-ILDs were the second most common (24.4%) category, with rheumatoid arthritis- ILDs being by far the most common CTD-ILD, followed by systemic sclerosis-ILDs, which were comparable to data from Bouros et al. [21] and Fischer et al. [20], emphasizing the important autoimmune contribution to ILD burden. A smaller group of cases (15.6%) had HP, which probably reflects under-recognition from a lack of environmental evaluation and a lack of lung biopsy confirmation in some cases. Occupational/environmental ILD (4.4%) and unclassifiable ILD (2.2%) were relatively rare, consistent with the need for better access to diagnosis and long-term evaluation that clarifies these entities [13, 15]. Overall, the present study supports the idea that IPF and CTD-ILDs are the major etiologies, and environmental exposures play a significant secondary role. The findings emphasise the importance of thorough clinical assessment, HRCT imaging, and multidisciplinary assessment for both correct classification, prognostication, and management of ILD patients in a regional setting.

Within the limitations of the current study, we found idiopathic interstitial pneumonias, especially IPF, were the commonly prevalent type of ILD, followed by CTD-associated ILD and hypersensitivity pneumonitis. Our study delineates the importance of HRCT pattern for recognition and use of multidisciplinary discussion between Pulmonologists, Physicians and Radiologists for accurate diagnosis and classification of ILD. Such an approach will lead to accurate diagnosis, early intervention, and improved outcomes.

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