Interstitial lung diseases (ILDs) are a diverse group of diffuse parenchymal lung disorders characterized by varying degrees of inflammation and fibrosis of the alveolar interstitium. They may occur idiopathically or be associated with identifiable factors such as connective tissue diseases, environmental or occupational exposures, drug-induced toxicity, or hypersensitivity reactions [1,2]. Among the idiopathic forms, idiopathic pulmonary fibrosis (IPF) is the most prevalent subtype, associated with a poor prognosis due to its progressive fibrosing nature [1].

The clinical presentation of ILDs is typically insidious and non-specific, with progressive exertional dyspnea and dry cough being the most common symptoms. These features often mimic other respiratory conditions, resulting in diagnostic delays [3]. Physical findings such as bibasal end-inspiratory crepitations and digital clubbing are useful clinical clues. Pulmonary function tests usually reveal a restrictive ventilatory pattern and reduced diffusing capacity for carbon monoxide (DLCO), while the six-minute walk test (6MWT) serves as a valuable tool for assessing functional status and exercise-induced desaturation [4].

High-resolution computed tomography (HRCT) has become central to the diagnosis of ILDs, enabling visualization of characteristic radiological patterns such as usual interstitial pneumonia (UIP), nonspecific interstitial pneumonia (NSIP), and hypersensitivity pneumonitis (HP) [2,5]. A comprehensive diagnostic approach incorporating clinical history, radiologic features, pulmonary function tests, and serologic markers is essential for accurate classification and effective management of ILDs.

In the Indian context, data on the clinical and radiological profile of ILD patients remains limited. This study was undertaken to evaluate the clinical presentation, risk factors, pulmonary function, and HRCT features of ILD patients presenting to a tertiary care hospital, with the aim of improving diagnostic accuracy and guiding appropriate management strategies.

Study Design and Setting:

This was a hospital-based, observational cross-sectional study conducted at the Government General and Chest Hospital, Hyderabad—a tertiary care referral center for pulmonary diseases in Telangana, India.

Study Duration:

The study was carried out over a period of twelve months, from February 2024 to January 2025.

Study Population:

The study included adult patients (≥18 years) who were diagnosed with interstitial lung disease (ILD) based on clinical evaluation and high-resolution computed tomography (HRCT) thorax findings. Patients presenting to the outpatient and inpatient departments of the hospital with respiratory symptoms suggestive of ILD were evaluated for inclusion.

Inclusion Criteria:

Patients aged 18 years and above.

Radiologically confirmed ILD based on HRCT findings.

Patients who provided informed consent for participation.

Exclusion Criteria:

Patients with known malignancy or active pulmonary tuberculosis.

Patients with incomplete clinical or radiological records.

Hemodynamically unstable patients or those unable to perform pulmonary function tests or 6MWT.

Data Collection:

After obtaining informed consent, a detailed clinical history including symptoms, duration, and occupational/environmental exposure was recorded. A thorough physical examination was performed. Relevant risk factors such as smoking status and family history were noted. All patients underwent:

Pulmonary function testing (PFT) using standard spirometry.

Six-minute Walk test (6MWT) to assess functional status and oxygen desaturation.

High-resolution computed tomography (HRCT) of the thorax to identify ILD patterns.

Serological investigations, including ANA, rheumatoid factor, and other connective tissue disease markers when indicated.

Final Diagnosis:

The diagnosis of specific ILD subtypes was based on a multidisciplinary approach incorporating clinical, radiological, and serological findings, consistent with current ATS/ERS guidelines.

Statistical Analysis:

Data were entered into Microsoft Excel and analyzed using SPSS version 25.0. Descriptive statistics such as means, standard deviations, frequencies, and percentages were used to summarize demographic and clinical characteristics. Associations between variables were evaluated using the Chi-square test for categorical data. A p-value < 0.05 was considered statistically significant.

A total of 100 patients diagnosed with interstitial lung disease (ILD) were included in the study. The mean age of the study population was 56.4 ± 12.8 years, with a predominance of females (58%) over males (42%). The most frequently affected age group was 51–70 years, accounting for 62% of cases. The most common presenting symptoms were dyspnea (92%) and dry cough (76%), followed by basal crepitations (83%) and digital clubbing (28%) (Table 1).

Table 1: Demographic and Clinical Characteristics (n = 100)

Regarding potential risk factors, smoking history was noted in 36% of patients, followed by organic dust exposure (24%), occupational exposure (16%), and a family history of ILD in 6% (Table 2).

Table 2: Risk Factors and History

Pulmonary function tests revealed a restrictive pattern in 81% of patients. The mean forced vital capacity (FVC) was 58.2 ± 14.5% predicted, and diffusing capacity for carbon monoxide (DLCO) was reduced in 88% of cases. The 6-minute walk test (6MWT) showed desaturation >4% in 65% of patients, with a mean distance walked of 312 ± 68 meters (Table 3).

Table 3: Pulmonary Function and Walk Test Results

Figure 1. Pulmonary Function and 6MWT Abnormalities in ILD Patients

High-resolution computed tomography (HRCT) of the thorax revealed characteristic radiological findings. Reticulations were observed in 86%, traction bronchiectasis in 54%, ground-glass opacities in 47%, and honeycombing in 39%. The predominant distribution was subpleural and basal, seen in 72% of cases (Table 4).

Table 4: Radiological Features on HRCT

Figure 2. Radiological Features on HRCT in ILD Patients

\Radiologically, the most common pattern identified was usual interstitial pneumonia (UIP) in 42%, followed by nonspecific interstitial pneumonia (NSIP) in 28%, and hypersensitivity pneumonitis (HP) in 15%. Based on the clinical-radiological correlation and serological evaluation, the final diagnoses included idiopathic pulmonary fibrosis (IPF) in 38%, connective tissue disease-associated ILD (CTD-ILD) in 20%, HP in 15%, and other patterns such as sarcoidosis and organizing pneumonia in 12% (Table 5).

Table 5: ILD Pattern and Final Diagnosis

This study provides valuable insights into the clinical, functional, and radiological characteristics of patients diagnosed with interstitial lung disease (ILD) at a tertiary care center in South India. The demographic profile, with a predominance of middle-aged individuals and a slight female majority (58%), aligns with regional and international data, such as that reported by Ghimire et al. in a tertiary center in Nepal, where ILD was most common in the fifth and sixth decades of life [6].

Dyspnea and dry cough were the most frequently reported symptoms in our study population, occurring in 92% and 76% of patients, respectively. These findings are consistent with global literature describing the typically insidious and non-specific clinical presentation of ILDs [7]. Basal end-inspiratory crepitations and digital clubbing, observed in 83% and 28% of patients respectively, remain useful bedside indicators of underlying fibrotic lung disease.

Risk factor analysis revealed smoking history in 36% of patients, and exposure to organic dust or occupational pollutants in 40%. These environmental triggers play a significant role in ILD pathogenesis, particularly in hypersensitivity pneumonitis (HP), which was suspected in 15% of our cases. This is consistent with reports of increased HP prevalence in rural and semi-urban populations, where exposure to bioaerosols is common [8].

Pulmonary function tests revealed a restrictive ventilatory defect in 81% of patients, and diffusion impairment (reduced DLCO) in 88%. The six-minute walk test showed desaturation >4% in 65%, underscoring the impact of ILD on functional capacity and oxygenation. These findings reflect those from Duchemann et al., who emphasized the utility of functional markers in disease severity assessment [8].

Radiologically, high-resolution computed tomography (HRCT) thorax revealed usual interstitial pneumonia (UIP) as the most common pattern (42%), followed by nonspecific interstitial pneumonia (NSIP) and HP. Subpleural reticulations, traction bronchiectasis, and honeycombing were prevalent features, indicating advanced fibrotic disease. This pattern distribution supports existing evidence that UIP is the predominant form of ILD and correlates closely with idiopathic pulmonary fibrosis (IPF) [7,9].

Regarding final diagnosis, IPF (38%) was the most frequently observed subtype, followed by connective tissue disease-associated ILD (20%) and HP (15%). The relatively high proportion of CTD-ILD may be attributed to increased awareness and improved access to autoimmune screening, such as antinuclear antibody (ANA) testing. Studies by Gupta et al. have demonstrated the diagnostic relevance of ANA patterns in detecting autoimmune involvement among ILD patients [11].

Additionally, the subset of patients showing features of interstitial pneumonia with autoimmune features (IPAF) highlights the importance of identifying overlapping clinical, radiologic, and serologic criteria. Previous studies, including those by Ahmad et al. and Oldham et al., have emphasized the need to categorize these patients appropriately for better prognostic assessment and management [9,10].

This study highlights the clinical and radiological spectrum of interstitial lung disease (ILD) in a tertiary care setting. Middle-aged adults, particularly females, were predominantly affected. Dyspnea and dry cough were the most common presenting symptoms. Smoking, environmental exposures, and occupational risk factors played a significant role in disease occurrence. Pulmonary function tests showed a restrictive pattern in most patients, and HRCT findings predominantly revealed UIP and NSIP patterns. Idiopathic pulmonary fibrosis emerged as the most frequent ILD subtype. Early recognition of symptoms, risk factor assessment, and HRCT-based classification are essential for timely diagnosis and appropriate management to improve patient outcomes in ILD.

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