Interstitial lung disease (ILD) encompasses a diverse group of disorders characterized by varying degrees of inflammation and fibrosis of the lung parenchyma, leading to impaired gas exchange and respiratory function. These conditions are often progressive and challenging to diagnose due to overlapping clinical and radiological presentations. 

The clinical spectrum of ILD ranges from mild dyspnea and dry cough to severe respiratory compromise, while radiological manifestations commonly include ground-glass opacities, reticulations, and honeycombing patterns observed on high-resolution computed tomography (HRCT). North India, like other regions with environmental and occupational hazards, may present unique patterns of ILD prevalence and subtypes due to factors such as exposure to dust, biomass fuels, and climate conditions.⁴ However, there is limited data on the clinical and radiological features specific to this geographical area, particularly in large cohorts. While prior studies in India have identified idiopathic pulmonary fibrosis (IPF) and hypersensitivity pneumonitis (HP) as prevalent forms of ILD, variations in disease phenotype and presentation remain underexplored.^5-8

The present study aims to contribute to the existing literature by expanding the sample size to provide a comprehensive understanding of the clinical and radiological spectrum of ILD in a North Indian state. By analyzing clinical presentations, imaging findings, and disease patterns, this research seeks to bridge knowledge gaps and inform better diagnostic and management strategies for patients with ILD in this region.

This prospective observational study was conducted in the Department of Radiodiagnosis at the Sheri-Kashmir Institute of Medical Sciences, Medical College, Bemina, Srinagar, between March 2023 and February 2024. The objective was to explore the clinical and radiological spectrum of interstitial lung disease (ILD) in patients referred for High Resolution CT (HRCT) scans of the chest. The study included all consecutive patients referred to the department with suspected ILD, based on clinical features, spirometry, and chest X-ray findings, who provided informed consent to participate. A total of 150 patients were enrolled in the study. Patients with recent or active infections, known tuberculosis, neoplastic diseases, or those who declined participation were excluded.

Data collection involved a detailed medical history focusing on presenting symptoms (such as cough, dyspnea, and chest pain), prior and coexisting medical comorbidities (e.g., diabetes, hypertension, autoimmune diseases), occupational history (such as exposure to asbestos or silica), environmental exposures (e.g., biomass fuel usage, air pollution), family history of ILD or lung diseases, and medications, especially those linked to drug-induced lung disease. Additional investigations performed for diagnosing ILD included haemogram, chest radiograph, sputum smear examination for acid-fast bacilli (AFB), Mantoux test, pulmonary function test (PFT), and serological tests such as serum anti-nuclear antibody (ANA), serum calcium, serum angiotensin-converting enzyme (ACE) levels, cytoplasmic antineutrophil cytoplasmic antibodies (c-ANCA), perinuclear anti-neutrophil cytoplasmic antibodies (p-ANCA), anti-topoisomerase I antibody (Scl-70), rheumatoid factor (RA), anti-cyclic citrullinated peptide antibodies (anti-CCP), and anti-double-stranded DNA (anti-dsDNA). Additional investigations, including 24-hour urinary calcium levels, were also recorded.

Histopathological investigations were conducted when indicated, using techniques such as bronchoalveolar lavage (BAL), transbronchial needle aspiration (TBNA), endobronchial biopsy, transbronchial lung biopsy (TBLB), surgical lung biopsy, and fine needle aspiration or biopsy of other affected sites, including skin. The diagnostic criteria for the primary ILD subtypes followed recognized guidelines. Idiopathic Pulmonary Fibrosis (IPF) was diagnosed according to the American Thoracic Society (ATS), European Respiratory Society (ERS), Japanese Respiratory Society, and Latin American Thoracic Association guidelines. The Idiopathic Interstitial Pneumonias (IIPs) were diagnosed based on the ATS/ERS Multidisciplinary Consensus Classification for IIPs. Sarcoidosis was diagnosed based on clinical and radiological findings, granulomatous inflammation in tissue specimens, and the exclusion of other causes such as tuberculosis. Hypersensitivity Pneumonitis (HP) was diagnosed with a history of exposure to organic dusts, HRCT findings, and histological confirmation of HP. Connective Tissue Disease-associated ILD (CTD-ILD) was diagnosed in the presence of a confirmed connective tissue disease (e.g., rheumatoid arthritis or systemic sclerosis) along with ILD evident on HRCT.

Statistical analysis was conducted using the Statistical Package for the Social Sciences (SPSS), version 20.0 (SPSS Inc., Chicago, Illinois, USA). Continuous variables were presented as mean ± standard deviation (SD), and categorical variables as frequencies and percentages. The significance of relationships between clinical, radiological, and histopathological features was determined using appropriate statistical tests. The study was approved by the institutional ethics committee of the Sheri-Kashmir Institute of Medical Sciences. Informed consent was obtained from all participants, and confidentiality of patient information was ensured throughout the study.

Table 1: Clinical Profile of the Patients

The study included a diverse patient population in terms of age, gender, clinical symptoms, and comorbidities. The majority of patients were aged 50-69 years (56.0%), followed by those aged 30-49 years (20.7%). A higher proportion of male patients (59.3%) were represented compared to females (40.7%). Nearly half of the patients were current or previous smokers (42.0%). In terms of clinical symptoms, the most common were exertional breathlessness (98.7%) and cough (96.0%). A smaller proportion of patients reported chest pain (22.0%), weight loss (27.3%), and arthralgia (20.7%). Other symptoms included lower extremity edema (16.0%), fever (3.3%), and skin rash (2.7%).

The most prevalent comorbidities in the study cohort were hypertension (70.7%), gastroesophageal reflux disease (62.7%), and obstructive sleep apnoea (30.7%). Other notable comorbid conditions included diabetes mellitus (22.0%), obesity (20.0%), and osteoarthritis (17.3%). Chronic kidney disease (12.7%), ischemic heart disease (10.0%), and hypothyroidism (7.3%) were less common.

Table 2: Radiological Abnormalities on HRCT Thorax of the Study Patients

Table 2 presents the radiological abnormalities observed on High-Resolution CT (HRCT) thorax in the study patients. The most common finding was ground glass opacities, present in 52.5% of patients. Interlobular septal thickening (39.3%) and intralobular septal thickening (34.4%) were also frequently observed. Honeycombing, a characteristic sign of advanced interstitial lung disease, was found in 28.7% of patients. Other radiological findings included peribronchovascular septal thickening (20.5%), mediastinal adenopathy (32.8%), and random nodules (20.5%). Less common findings included centrilobular nodules (4.9%), centrilobular emphysema (9.8%), mosaic attenuation (4.1%), and consolidation (5.7%). Traction bronchiectasis, a sign of fibrotic lung disease, was noted in 26.3% of patients, and cysts were identified in 3.3% of cases. These findings highlight the wide range of radiological abnormalities seen in interstitial lung disease, providing important diagnostic clues.

Table 3: Distribution of Radiological Abnormalities on HRCT Thorax

Table 3 shows the distribution of radiological abnormalities observed on HRCT thorax in the study patients. A diffuse pattern, involving both upper/middle and lower lobes, was the most common, seen in 41.8% of patients. Abnormalities predominantly affecting the upper/middle lobes were observed in 33.6% of cases, while 24.6% of patients had radiological findings primarily in the lower lobes. This distribution highlights the variability of interstitial lung disease patterns and underscores the importance of careful interpretation of HRCT findings in different lobar regions.

Table 4: Final Diagnosis of the Study Patients

Table 4 presents the final diagnoses of the study patients, showing the distribution of different interstitial lung diseases (ILD). The most common diagnosis was Idiopathic Pulmonary Fibrosis (IPF), which accounted for 29.33% of cases. Non-IPF Idiopathic Interstitial Pneumonia followed with 24%, and Nonspecific Interstitial Pneumonia was the third most frequent at 16.67%. Other notable diagnoses included Hypersensitivity Pneumonitis (16%), Connective Tissue Disease-associated ILD (10.67%), and Sarcoidosis (8%). Less common conditions such as Acute Interstitial Pneumonia, Cryptogenic Organizing Pneumonia, and Langerhans Cell Histiocytosis were diagnosed in 0.67% of patients each. Additionally, 2.67% of cases were classified as Unclassified ILD.

This study evaluated the radiological spectrum of various interstitial lung diseases (ILDs). Epidemiological data regarding ILD in India is limited, with only a few sporadic studies published in the literature.^9-13 These studies present sparse and sometimes conflicting data. The largest prospective ILD registry published in 2016 provides minimal representation from our state.¹⁴ Jammu and Kashmir, as the northernmost state of India, differs significantly from the rest of the country in terms of climate, environment, culture, ethnicity, and occupational patterns. These unique factors motivated us to conduct this study to identify the prevalent types of ILD in our region and explore their radiological patterns.

The mean age of the patients in our study was 64.1 ± 9.7 years, ranging from 18 to 82 years. This is considerably higher than what has been reported in previous Indian studies.^19,23 In the ILD India registry, the mean age at the time of presentation was 55.3 years [14]. Similarly, studies by Dhooria S et al., Das V et al., and Kumar R et al. reported mean ages of 50.6 years, 53.99 years, and 44.24 years, respectively.^21,23 Thus, our population presented almost a decade or more later than the populations in these earlier studies. One possible explanation for this could be the late onset of the disease in our distinct population, as previously mentioned. Additionally, Idiopathic Pulmonary Fibrosis (IPF), which was the most common ILD in our study, was associated with older patients (mean age 69.3 ± 13.6 years) compared to other subgroups of ILD, a finding that has been consistently observed in other studies.^14,21,23

In our study, males comprised the majority (59.3%) of patients, whereas previous studies have typically reported nearly equal sex distribution or a slight female predominance in ILD patients.^5-14 Within the IPF subgroup, 83.3% of the patients were male, which aligns with findings from other studies that have shown male dominance in IPF cases.^14,21,23 This male predominance may be influenced by factors such as the societal tendency for poorer healthcare-seeking behavior among females in our region. Smoking, an important environmental risk factor for ILD, was reported by 42% of patients in our study, with 61.1% of IPF patients having a history of smoking. This prevalence is more than double that reported in previous studies.^21-23 This notably high smoking prevalence could partly be attributed to the elevated stress levels in our population, stemming from the ongoing political turmoil in the region. The mean duration of symptoms before diagnosis in the present study was almost 3 years, which is comparable to the 3.07 years reported by Kumar R et al..²¹ However, this duration is considerably shorter than the 4.1 years reported in the ILD India registry and the 6 years observed in a large study by Dhooria S et al.^14-23 This discrepancy could be attributed to differences in the types and patterns of ILD observed in these studies, earlier referral of patients in our region to higher centers for more comprehensive diagnostic evaluation, or potentially more rapid symptomatic progression of ILD in our population.

In terms of clinical presentation, exertional breathlessness (98.7%) and cough (96%) were the most common symptoms reported by our patients, followed by weight loss (27%), chest pain (22%), and arthralgia (20.7%). Fever and skin rash were uncommon, with 3.3% and 2.7% of patients presenting with these symptoms, respectively. The clinical symptomatology in our study was consistent with findings from previous studies.^5-14,21-23 Comorbidities play an important role in the clinical course and long-term prognosis of ILD patients. In our study, the most frequently observed comorbidities were hypertension (70.7%) and gastroesophageal reflux disease (62.7%). Other common comorbidities included obstructive sleep apnoea (30.7%), diabetes mellitus (22%), obesity (20%), osteoarthritis (17.3%), chronic kidney disease (12.7%), ischemic heart disease (10%), and hypothyroidism (7.3%). These findings were similar to those reported in previous studies.^5-14,21-23  A history of tuberculosis or antitubercular therapy intake was observed in almost 8.5% of patients in our study, which is nearly half the prevalence reported in previous Indian studies.^21-23  In the ILD India registry, 15.5% of patients had a prior history of tuberculosis, while Kumar R et al. reported antitubercular therapy intake in 14.9% of patients, and Dhooria S et al. noted a history of tuberculosis in 18.4% of patients diagnosed with ILD in tertiary care hospitals of India.^14,21-23  The lower prevalence of tuberculosis in our study may be due to either a lower overall prevalence in our population or a higher threshold among physicians for prescribing antitubercular therapy. Similar to previous studies, the history of antitubercular therapy intake was most frequently seen among patients diagnosed with sarcoidosis and Gujjar lung (4.8% and 1.7%, respectively).^21-26 The clinical and radiological similarities between tuberculosis, sarcoidosis, and Gujjar lung often lead to misdiagnosis and the unnecessary prescription of antitubercular therapy for these patients.

In the present study, the most common high-resolution computed tomography (HRCT) findings included ground glass opacities (52.5%), interlobular septal thickening (39.3%), intralobular septal thickening (34.4%), honeycombing (28.7%), and mediastinal adenopathy (32.8%). Random nodules were observed in 20.5% of patients, while peribronchovascular septal thickening was present in 20.5% of cases. Traction bronchiectasis was noted in 26.3% of patients, and centrilobular emphysema was observed in 9.8% of patients, predominantly in those with idiopathic pulmonary fibrosis (IPF). The most prevalent patterns of lung involvement were diffuse (41.8%), followed by predominant involvement of the upper/middle lobes (33.6%) and lower lobes (24.6%). In comparison with previously reported studies, our study found a higher frequency of ground glass opacities and a diffuse pattern of lung involvement .^9-13,21-23  The most common interstitial lung disease (ILD) observed in this study was idiopathic pulmonary fibrosis (29.33%), followed by non-IPF idiopathic interstitial pneumonia (IIP) at 24%. Among the non-IPF IIPs, nonspecific interstitial pneumonia (NSIP) was the most prevalent (16.67%), with cryptogenic organizing pneumonia and respiratory bronchiolitis-associated ILD observed in 2.67% and 3.33% of patients, respectively. Hypersensitivity pneumonitis was the third most common diagnosis (16%), followed by connective tissue disease-associated ILD (10.6%). Sarcoidosis was diagnosed in 8% of patients, while occupational lung disease was present in 4%. These findings are consistent with those from previous studies, although varying prevalences of different ILD subtypes have been reported in the literature. ^{9-14, 21-23} In a study by Dhooria S. et al., which included 803 subjects, sarcoidosis was the most common ILD (42.2%), followed by IPF (21.2%). Connective tissue disease-associated ILDs, hypersensitivity pneumonitis, and non-IPF IIPs were diagnosed in 12.7%, 10.7%, and 9.2% of the subjects, respectively.²³ Similarly, Kumar R. et al. reported sarcoidosis as the most common ILD (37.3%), followed by IPF (27.6%) and NSIP (25.6%).²¹ In contrast, the multicenter ILD India registry, which included 1,084 patients from 27 centers in India, reported hypersensitivity pneumonitis as the most common ILD (47.3%). Other diagnoses in this study included connective tissue disease-associated ILD (13.9%), IPF (13.7%), idiopathic nonspecific interstitial pneumonia (iNSIP) (8.5%), sarcoidosis (8%), pneumoconiosis (3%), and other ILDs (5.7%).¹⁴ The notably high prevalence of hypersensitivity pneumonitis in this registry has been subject to criticism due to several limitations. The study was affected by significant selection bias, as patient enrollment was non-consecutive and drawn from various small hospitals and scattered clinics. Additionally, histopathological confirmation was available for only 7.5% of patients who underwent lung biopsy, and a high proportion (48.1%) of patients were casually diagnosed with air-cooler-induced hypersensitivity pneumonitis without establishing a cause-and-effect relationship. In another study by Das V. et al., IPF was found to be the most prevalent subtype of ILD, constituting 29.29% of cases, followed by NSIP (27.14%) and connective tissue disease-associated ILD (15.71%). Sarcoidosis and hypersensitivity pneumonitis each constituted 8.57% of cases.²² These findings were similar to those observed in our study. The divergent results across Indian studies may be attributed to the diversity of patient populations, as India is a vast country with varied social, cultural, occupational, and environmental factors. Additionally, differences in the availability and access to healthcare facilities, as well as variability in data collection protocols, diagnostic criteria, and categorization strategies, may contribute to the observed discrepancies. A rare yet distinctive form of interstitial lung disease (ILD) found in our region is Gujjar lung, an environmental ILD caused by indoor air pollution from pinewood smoke. In the present study, Gujjar lung was diagnosed in 2.67% of ILD patients. This condition predominantly affects individuals from the Gujjar community, a cattle-rearing socioethnic group residing in the high-altitude, hilly regions of the Indian subcontinent.^23-26 The term "Gujjar lung" was first introduced in 1991 by Dhar and Pathania from Kashmir, who observed miliary mottling and a reticulonodular pattern on chest radiographs in patients from this community, which did not respond to empirical antitubercular therapy (ATT).²⁴ Lung biopsies in these patients revealed anthracotic nodules, carbon-laden macrophages, and fibrosis. The authors attributed these findings to indoor air pollution from biomass combustion, specifically pinewood smoke. These observations have since been validated by multiple subsequent studies.^25,26

In conclusion, this study provides a comprehensive overview of the demographic, clinical, and radiological characteristics of patients with interstitial lung disease (ILD). The findings highlight a diverse patient population with a wide range of clinical presentations and comorbidities, emphasizing the complexity of diagnosing and managing ILD. The most common clinical symptoms, such as exertional breathlessness and cough, were observed across a majority of patients, while a variety of radiological abnormalities were identified on High-Resolution CT (HRCT), underscoring the varied patterns of lung involvement in ILD. The diagnostic distribution revealed a predominance of Idiopathic Pulmonary Fibrosis, followed by other interstitial lung diseases, illustrating the need for careful evaluation to differentiate between different ILD subtypes. These results reinforce the importance of a thorough, multidisciplinary approach in diagnosing ILD, incorporating clinical, radiological, and histopathological data to guide optimal patient management.

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