Idiopathic inflammatory myopathies comprise a heterogeneous group of autoimmune disorders, including dermatomyositis (DM), polymyositis (PM), immune-mediated necrotizing myopathy (IMNM), inclusion body myositis (IBM), clinically amyopathic dermatomyositis (CADM), and overlap myositis (OM). These subtypes differ in their clinical manifestations, serological profiles, pathological findings, and risk of developing interstitial lung disease (ILD), with anti-synthetase syndrome and dermatomyositis showing particularly high rates of pulmonary involvement. These systems are particularly observed in the lungs. The IIMs are highly representative of lung inflammation and autoimmune diseases. Interstitial lung diseases (ILDs) are very common in IIMs. IIMs and ILDs have very high mortality and morbidity. The recent studies revealed that, the incidence and prevalence of IIM is 0.1 – 2.0 cases per 100,000 person years and 2 – 25 cases per 100,000 population respectively {1,2}. Due to the difference in methods of classification, and disease recognition, there is a variation in incidence and prevalence of IIMs with respect to geographical location. ILD occurs at 20 – 65% of the time and with various autoantibodies and various myositis types {3}. A common presentation of ILD with IIM is dyspnea, cough and poor lung function. There is a high mortality risk with rapid progression of ILD, and this is seen with high aggressive immunosuppressive therapy. Now, HRCT is the gold standard in imaging of IIM and ILD. There is a very high sensitivity of HRCT to detect early ILDs {4}. Normal HRCT of lung reveals ground glass opacities, bronchiectasis, reticulations and fibrosis etc. Early Interstitial Lung disease with Non-specific Interstitial Pneumonitis and Organizing Pneumonitis can be hard to differentiate from Usual Interstitial Pneumonitis but the imaging correlates and provides an indication of the severity of the disease and clinical outcomes of the patient. Recent cohort studies have revealed that high resolution computed tomography (HRCT) scan patterns of extensive ground-glass opacities and reticular patterns are independent predictors of rapid progression of interstitial lung disease (ILD) and poor prognosis in patients with Idiopathic Inflammatory Myositis (IIM). This underscores the importance of HRCT while considering risks and making treatment decisions. {5,6}

This cross-sectional study was conducted in the Department of Chest Medicine (Ward-12), Jinnah Postgraduate Medical Centre (JPMC), Karachi, Pakistan, after obtaining approval from the Institutional Review Board (IRB) of JPMC. The study was carried out over a period of six months. Adult patients (≥18 years) with idiopathic inflammatory myopathy (IIM) who underwent high-resolution computed tomography (HRCT) of the chest for suspected interstitial lung disease (ILD) were enrolled using consecutive sampling. The diagnosis of idiopathic inflammatory myopathy (IIM) was established according to the 2017 European League Against Rheumatism/American College of Rheumatology (EULAR/ACR) Classification Criteria for adult idiopathic inflammatory myopathies. A sample size of 182 patients was calculated using the WHO formula for a single population proportion with prevalence of IIM with ILD as 36.6%, 95% Confidence interval with 7% margin of error as per the Laporte et al. report. The sample size was determined using non-probability method, consecutive sampling. Patients who did not have chronic ILD (excluding IIM), poor quality of HRCT or refused were excluded. Assessment for IIM was done with the help of a structured proforma in which demographic and clinical information of consenting patients was recorded. This included (but was not limited to) age, sex, smoking history, length of illness, clinical symptoms and other appropriate laboratory evaluations. The HRCT scans were done per the department’s imaging protocol. Clinical information was given independently and two consultant radiologists independently evaluated the images. The assessed features of the reviewed images included the presence of ground glass opacities, reticular patterns, bronchiectasis, honeycombing, interlobular septal thickening and other features. Also, the predominant HRCT pattern of NSIP, OP or UIP was evaluated and reported. Data was analyzed using SPSS for Windows (version 26.0). Continuous variables were presented as means ± SD or medians (interquartiles). Categorical variables were presented as frequencies and percentages. Chi-square or Fisher's exact test was used to assess the association of the features of HRCT imaging and ILD associated with IIM. P-values < 0.05 were deemed as statistically significant. All the procedures of this study followed the ethical requirements and rights of the subjects in compliance with the Declaration of Helsinki.

A total of 182 patients with idiopathic inflammatory myopathy (IIM) who underwent high-resolution computed tomography (HRCT) of the chest for suspected interstitial lung disease (ILD) were included in the study. The mean age of the participants was 46.8 ± 13.2 years (range: 19–78 years). The majority were female (116, 63.7%), while 66 (36.3%) were male. The median duration of IIM symptoms was 18 months (IQR: 10–30 months). A history of smoking was reported by 42 (23.1%) participants. The baseline demographic and clinical characteristics of the study population are presented in Table 1.

Among the 182 participants, 72 (39.6%) were diagnosed with IIM-associated interstitial lung disease (IIM-ILD), whereas 110 (60.4%) had no evidence of ILD.

The distribution of HRCT imaging findings according to ILD status is presented in Table 2. Ground-glass opacities were the most common HRCT abnormality and were observed in 61 (84.7%) patients with ILD compared with 18 (16.4%) patients without ILD (p < 0.001). Reticular opacities were identified in 49 (68.1%) patients with ILD and 15 (13.6%) patients without ILD (p < 0.001). Traction bronchiectasis was present in 32 (44.4%) patients with ILD compared with 8 (7.3%) patients without ILD (p < 0.001). Honeycombing was observed in 16 (22.2%) patients with ILD and 3 (2.7%) patients without ILD (p < 0.001). Consolidation was present in 21 (29.2%) patients with ILD compared with 11 (10.0%) patients without ILD (p = 0.001), indicating a significant association between these HRCT findings and IIM-associated ILD.

The predominant HRCT patterns among patients with IIM-associated ILD are shown in Table 3. Non-specific interstitial pneumonia (NSIP) was the most frequent radiological pattern, identified in 44 (61.1%) patients, followed by organizing pneumonia (OP) in 17 (23.6%), usual interstitial pneumonia (UIP) in 8 (11.1%), and other HRCT patterns in 3 (4.2%) patients.

Table 1. Baseline demographic and clinical characteristics of the study participants (n=182)

Table 2. HRCT imaging findings according to ILD status

Table 3. Predominant HRCT patterns among patients with IIM-associated ILD (n=72)

This current study examines the impact of high resolution computed tomography on identifying interstitial lung disease and the role high resolution computed tomography plays on assessing pulmonary interstitial involvement on idiopathic inflammatory myopathy on the patients diagnosed with idiopathic inflammatory myopathy. The American Thoracic Society/European Respiratory Society classification states that high resolution computed tomography is capable of distinguishing the major patterns of interstitial lung disease (such as organizing pneumonia, nonspecific interstitial pneumonia, and usual interstitial pneumonia) discovered in the inflammatory myopathy disorders {7}. In high resolution computed tomography, ground glass opacity was the most common finding based on our finding. Ground glass opacity (GGO) has also been found recently as the earliest sign of inflammatory lung disease in patients with idiopathic inflammatory myopathy (IIM). Pathologically, the opacities of the ground glass are the first step in the inflammatory and interstitial pulmonary edema and the first step in pulmonary fibrosis. Therefore, their prompt discovery warrants the administration of immunosuppressive therapy {8,9}. The presence of additional reticular opacities and traction bronchiectasis represents chronic interstitial remodeling and a progressive pulmonary fibrosis which affect the clinical outcome of the patient and lead to a progressive decline in pulmonary function {8,10}. HRCT NSIP, HRCT OP and HRCT UIP were observed most commonly in our patients. As mentioned in recent systematic reviews, NSIP is very frequently the most commonly observed CT pattern in ILD associated with CTDs and in inflammatory myopathies {7,11,12}. NSIP is associated with greater inflammatory process than UIP, and less irreversible fibrosis, and is associated with a more favorable response to treatment with corticosteroids, and to immunosuppression. On the other hand, UIP along with honeycombing is a picture of advanced fibrosis and a poor prognosis {11,12}. The strengths of this study are that there were a large number of patients and a standardized HRCT protocol, and the assessment of HRCT was independent and carried out by the consultant radiologists. The main limitations are its cross sectional, single center study design; lack of pulmonary functioning tests; myositis specific auto antibodies; and lack follow up. The authors of this study endorse the importance of early HRCT in patients suspected of having an inflammatory myopathy. If the characteristic pattern of HRCT is recognized, then diagnosis is more likely to be made in a timely fashion. This will, in turn, lead a more appropriate treatment and a more favorable prognosis. This will require further studies of greater size and scope and of a more prospective design, emphasizing imaging and inflammatory markers, as well as evaluation of pulmonary function {13}.

HRCT is a good imaging tool for early detection and analysis of interstitial lung disease (ILD) in patients with idiopathic inflammatory myopathy (IIM). ILD related to IIM is associated with ground glass opacities, reticular opacities, traction bronchiectasis and consolidation; the major HRCT pattern is non-specific interstitial pneumonia (NSIP). HRCT is beneficial in the early identification, and diagnosis, of the patterns guiding the clinician in the initiation of the best therapeutic alternatives. By early starting of the multidisciplinary team, the characteristic HRCT features recognizing patterns of IIM related ILD and NSIP will most likely improve patient outcomes. This goal requires more studies, multi-center and prospective in nature, to be able to determine the long-term significance of the results.

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