The study was hospital-based cross-sectional study conducted during November 2014 to August 2016. The Institutional Review Board approval for conducting this study was obtained and informed consent for study was taken from all patients. A total of 60 patients referred to Department of Radio-Diagnosis, Rajindra Hospital, Patiala with clinical diagnosis of ILD were included in this study. Both male and female patients with clinical profile of dyspnea and chronic cough and X-ray findings suspicious of ILD were included in this study. Patients of varied socioeconomic strata and literacy levels were included. Cases of infective aetiology (HIV, Tuberculosis etc.,) or malignant aetiology as well as chronic obstructive pulmonary disease were excluded. Detailed proforma was filled for all those patients who met with the inclusion criteria. The proforma included the patient’s name, age, sex, address, registration number, complaints, risk factors, previous medical or surgical history, laboratory investigations and spirometric findings. Complaints were noted in detail and the severity grading of various complaints were done e.g., dyspnoea, measured as per modified Medical Research Council (mMRC) Dyspnoea scale [3], Dry Cough (based on 10-point Visual Analogue-type response scales (VAS) [4], Generalized weakness (based on patient’s subjective perception), Weight loss (Unintentional weight loss, of at least 5% of the patient’s usual body weight within the preceding 6 to 12 months), Chest pain (VAS, scale 1-10) [5-7] and Joint pain (based on patient’s subjective perception) etc., Using the standard protocol, HRCT chest was done on 6 slice Siemens-Somatom CT scanner in supine position and it was read by a single experienced radiologist. Parenchymal abnormalities were categorized into four main and 12 other associated features with their distribution along the lung zones. HRCT severity score [Table/Fig-1] was calculated based on Semi-quantitative scoring method used by Warrick JH et al., [8].

Spirometry was performed using Medisoft Spiro Air dry rolling seal spirometer. The details of the procedure were explained to all patients and a written consent was obtained from all. Patients exhaled for at least six seconds and stopped when there was no volume change for one second. At least three acceptable spirograms were obtained with a maximum of 8 trials. The largest FVC and FEV1 from acceptable curves were obtained according to American Thoracic society guidelines. Thereafter, these spirometry indices were correlated with HRCT scores.

Microsoft Excel version 2007 was used for Standard statistical analysis. Categorical variables were presented in number and percentage (%) and continuous variables were presented as mean ± SD and median. Age was compared using Unpaired t-test between male and female. Qualitative variables were correlated using Chi-Square test/Fisher’s-exact test. Pearson correlation coefficient was used to correlate scores with FEV1, VC and FVC. A p-value of <0.05 was considered statistically significant. The data was entered in MS EXCEL spreadsheet and analysis was done using Statistical Package for Social Sciences (SPSS) version 21.0.

Majority of the patients 46.67% (n=28) were between the ages of 51-70 years, and comprised of 13 males and 15 females. The major complaints were gradual onset dyspnea/dyspnea on exertion, followed by dry cough and generalized weakness. Few patients had associated symptoms like fever, joint pain, chest pain and weight loss etc.

The most common interstitial lung disease found in our study was Usual Interstitial Pneumonia (UIP)/Idiopathic Pulmonary Fibrosis (IPF) (n=33; 55%) followed by nonspecific interstitial pneumonia (NSIP) (n=9; 15%), sarcoidosis (n=5; 8.3%), hypersensitivity pneumonitis (HSP, n=5; 8.3%), respiratory bronchiolitis associated RB-ILD (n=1; 1.67%), Desquamative Interstitial Pneumonia (DIP, n=1;1.67%) and unclassified Idiopathic Interstitial Pneumonia (IIP, n=6; 10.0%).

The most common finding observed on HRCT was septal or subpleural lines. Ground Glass Opacities (GGO’s), irregular pleural margins and honeycombing were also commonly observed [Table/Fig-2].

Severity score of all the ILD patients was calculated, using a semi-quantitative scoring system based on study by Warrick JH et al., [8], wherein GGO’s, Septal/subpleural lines, pleural irregularities, honeycombing and subpleural cysts were taken into consideration. Extent scores were based on number of segments involved. [Table/Fig-3,4].

Spirometry was performed in all the cases. Majority of the patients, 36.67% (n=22) in the study showed severely low FVC. 16.67% (n=8) had moderately low and 23.33% (n=14) had mildly low FVC. 23.33% of patients had severe affection of VC (n=14). FEV1 of majority of the patients were normal i.e., 33.33%, (n=20) of ILD, showed a normal FEV1 where as 21.67% had a moderate affection of FEV1 and only 1.67% had very severe affection of the FEV1.

The correlation between the HRCT severity and spirometric severity is established as in [Table/Fig-5]. The HRCT images showing changing indicating IPF, NSIP, HSP, sarcoidosis, DIP and unclassified IIP [Table/Fig-6,7,8,9,10 and 11].

[Table/Fig-6]:

a,b) HRCT shows bilateral diffuse extensive fibrosis with septal thickening, honeycombing (straight arrow), subpleural cysts (open blue arrow) and traction bronchiectasis (curved arrow) having mid and basal predominance in subpleural region bilaterally. Findings indicate usual interstitial pneumonia/idiopathic pulmonary fibrosis.

[Table/Fig-7]:

a,b) HRCT images show bilateral diffuse interstitial lung disease in the form of interlobular and intralobular septal thickening (arrowhead) and subpleural lines (arrow). Pleural irregularities are also seen (open blue arrow). Findings indicate Nonspecific Interstitial Pneumonia.

[Table/Fig-8]:

a,b) Show bilateral symmetrical ground glass opacities (white arrows) in mid and basal lung zones with round centri-lobular opacities having geographical distribution of increased, decreased (red arrow) and normal lung attenuation giving head cheese sign. Imaging findings are consistent with Hypersensitivity Pneumonitis.

[Table/Fig-9]:

a-c) HRCT images show nodular opacities along fissures and lymphatics. Bilateral hilar (thick red arrows) and right paratracheal (thin white arrow) lymphadenopathy seen giving 1-2-3 sign in a case of Sarcoidosis.

[Table/Fig-10]:

a,b) HRCT images show bilateral symmetrical ground glass opacities with reticular changes more in peripheral region. Bronchioloectatic changes with broncho-vascular interstitial thickening (straight red arrow) and minimal honeycombing (open blue arrow) are seen. Enlarged pulmonary artery and bilateral pleural effusion (star) are also seen. Imaging features are consistent with Desquamative Interstitial Pneumonia.

[Table/Fig-11]:

a,b) HRCT image shows areas of ground glass opacities (arrows) and centrilobular nodules superimposed on ground glass opacities. Imaging features and history of smoking are in favour of respiratory bronchiolitis associated interstitial lung disease.

Out of sixty cases in our study 54 (90%) cases showed specific patterns of ILD and six cases (10%) showed nonspecific patterns and were classified under unclassified IIP. Analysis of age distribution of patients in our study showed a wide range with maximum percentage of patients 46.67% in the age group 51-70. Study by Jindal SK et al., showed almost similar age of presentation with maximum patients in age group 40-70 years of age [9]. Coultas DB et al., found the age of presentation almost a decade later (61-70 years) [10].

In our study, 56.67% patients were females and 43.33% were males. It closely correlated with the study by Jindal SK et al., in which female and male incidence was found to be 57.4% and 42.4% respectively [9]. Similar results were seen in other studies done by Devi MS and Haorongbam S, and Patil PB et al., [11,12].

In our study, the maximum duration of illness was found to be 5 years and the minimum duration of illness was found to be 2 months. Mean duration of illness of the patients was 3 years with SD of 1.6. Maximum patients presented between 1-5 years. Similar duration of illness was found in Indian study done by Gagiya AK et al., in which, maximum patients presented before 5 years of onset of illness and majority presented between 1-3 years [13].

In our study, the most common presenting complaint was gradual onset dyspnoea (n=57; 95 %), followed by dry cough (n=53; 88.3%) and generalized weakness (n=48; 80%). Some patients also had varying symptoms like fever, joint pain, chest pain and weight loss etc. This was in accordance with study by Patil PB et al., with most common presenting complaint being progressive dyspnea (seen in 96% patients), dry cough (in 74%) and associated joint pain (in 44%) [12]. Study by Perez RL and Weinrib L et al., showed similar clinical profile, with progressive dyspnea on exertion and a dry cough as major complaints [14,15]. According to the study by Bhadke BB et al., predominant symptom of ILD was dyspnea on exertion and the degree of dyspnea was closely related to the disease severity and prognosis [16]. Cough was the second most frequent symptom found in the study.

HRCT in disease spectrum of interstitial lung diseases: In our study the most common interstitial lung disease reported on HRCT was usual interstitial pneumonia (UIP)/Idiopathic Pulmonary Fibrosis (IPF), followed by Nonspecific Interstitial Pneumonia (NSIP), sarcoidosis and hypersensitivity pneumonitis [Table/Fig-12,13].

Six cases, did not fit into any particular HRCT imaging pattern of ILD and as the Lung biopsy was not done in all cases, diagnosis could not be reached in these cases. So, these cases are included in unclassified IIP category. [Table/Fig-12,13] shows comparison of previous done studies with present study.

HRCT features of different types of ILDs and various comparison studies are summarized in [Table/Fig-14,15,16,17,18 and 19].

Correlation of HRCT severity score and extent score with spirometry: In our study, special efforts were made to establish correlation between HRCT scores and Pulmonary function tests. Correlation between Semi-quantitative HRCT severity score and extent score with the FVC, VC and FEV1 was studied [Table/Fig-3,4,5].

Correlation coefficient between HRCT score and FVC: Present study showed significant inverse correlation of HRCT severity score with the FVC (r= -0.578, p-value <0.0001). These findings correlated well with the similar study done by Xaubet A et al., in 39 untreated patients with idiopathic pulmonary fibrosis [31], in which the HRCT score showed a moderate but significant correlation with FVC (r = -0.46, p = 0. 003). Xaubet A et al., also did the correlational study of HRCT extent with the FVC and observed an inverse relationship (r = -0. 51, p = 0.01) [31]. In our study, also a similar negative correlation between HRCT extent score and Pulmonary function test was found {FVC (r= -0.506) with P-value of <0.0001}. Study done by Isaac BTJ et al., in 2015, in 94 patients of IIP, in South India also showed an inverse correlation between the HRCT scores and FVC (r= −0.48) [32]. Mura M et al., and Best AC et al., had also observed a good negative correlation of FVC with HRCT scores [33,34].

Correlation coefficient between HRCT score and VC: Our present study also showed inverse correlation of HRCT severity score with the VC (r= -0.295, p-value <0.0001). This observation was similar as that seen by Battista G et al., who used HRCT visual score [35]. A decrease in the VC and diffusing capacity of lung for carbon monoxide (DLCO) was observed in serial follow up study of the patients with HRCT progression of the disease. O’Donnell D [36] had opined that in restrictive lung diseases, both the VC and FVC are reduced, but the FVC is usually decreased to a relatively lesser extent, as opposed to our study, in which a greater decrease in FVC was seen as compared to VC.

Correlation coefficient between HRCT score and FEV1: In the present study, negative correlation was also seen between the HRCT severity score and FEV1, with correlation coefficient of (-0.271). This correlation seemed less significant in comparison to the relationship between the HRCT severity with FVC and VC. This was in consistence with the study done by Ooi GC et al., in patients with systemic sclerosis [37], where an inverse correlation between HRCT scores and FEV1 was seen (r=–0.37, p=0.03). Same study found stronger inverse correlation of HRCT score with FVC (r=−0.43, p=0.008).

Biederer J et al., in his study of correlation between HRCT findings and pulmonary function tests, in 53 patients of ILD, observed that lesions in HRCT correlated weakly with FEV1 (r=−0.31; p<0.01) [38]. Same study found a much stronger correlation between the HRCT severity with the diffusion capacity (r=−0.54; p<0.001). As there is a definite correlation between the HRCT severity and spirometric findings, spirometric indices can be used in the follow up of patients with ILD.

This was not a prospective study and critically ill patients could not perform spirometric manoeuvers.

Spirometry is a simple, noninvasive modality to measure severity of ILD and help in its objective assessment. It is bereft of all radiation hazards and can be conveniently performed in pregnant patients and young children. Being cheaper it is more readily available than HRCT and it is a powerful tool that can be used to detect and manage patients with restrictive lung disorders. HRCT is invaluable in characterizing the disease process, but it cannot assess the physiological lung functions. As the severity and extent scores of HRCT have an inverse relationship with the spirometric indices in ILD, spirometry can provide a viable alternative to assess the disease severity.