Diabetes mellitus is a major global health problem. In 2021, an estimated 537 million adults were living with diabetes, and this number is projected to rise substantially by 2045 [1]. Clinical care has traditionally focused on retinopathy, nephropathy, neuropathy, and cardiovascular disease. Pulmonary involvement receives less attention even though diabetes can affect the lung's connective tissue, microvasculature, and mechanical properties [2-6].

Chronic hyperglycemia may injure lung tissue through endothelial dysfunction, oxidative stress, low-grade inflammation, and accumulation of advanced glycation end products. These mechanisms can increase vascular permeability and promote extracellular-matrix remodeling and fibrosis [7-9]. Consistent with this biological model, adults with type 2 diabetes have shown modest reductions in forced vital capacity, forced expiratory volume in one second, and diffusing capacity in observational studies [10]. Diabetes also increases susceptibility to respiratory infection, including tuberculosis, which remains clinically important in India [11].

High-resolution chest CT can identify ground-glass opacity, interstitial thickening, reticulation, nodules, and early fibrotic change. Perfusion and quantitative CT studies have also described pulmonary microvascular and parenchymal differences in patients with diabetes [12-14]. However, evidence remains insufficient to define which patients should undergo imaging in the absence of respiratory symptoms.

This study aimed to describe the prevalence and pattern of chest CT abnormalities in adults with type 2 diabetes mellitus and to examine whether these findings were associated with HbA1c and duration of diabetes.

Study Design and Setting A cross-sectional observational study was conducted in the Department of Radiodiagnosis in collaboration with the Department of Endocrinology at a tertiary care hospital in Tamil Nadu, India. Recruitment and imaging took place from May 2018 through March 2019. The calculated minimum sample was 58 participants; 60 were enrolled [15]. Participants Adults aged 18 years or older with type 2 diabetes mellitus diagnosed according to American Diabetes Association criteria were eligible [16]. Participants were required to provide written informed consent and to have no previous diagnosis of primary pulmonary disease. Exclusion criteria included type 1 or secondary diabetes, chronic obstructive pulmonary disease, bronchial asthma, non-diabetic interstitial lung disease, active pulmonary tuberculosis, lung malignancy, acute respiratory infection at enrollment, pregnancy, contraindication to CT, and substantial occupational exposure to pulmonary toxins. Clinical and Laboratory Assessment A structured proforma recorded age, sex, residence, smoking and occupational history, diabetes duration, treatment, and documented diabetic complications. Fasting plasma glucose, postprandial plasma glucose, and HbA1c were measured within one week of CT examination using routine laboratory methods [17]. Glycemic control was categorized as HbA1c <7% or HbA1c ≥7%. CT Acquisition and Image Assessment Chest CT was performed on a 128-slice multidetector scanner (Somatom Definition AS, Siemens Healthineers). Participants were scanned supine at end-inspiration using a low-dose protocol. Images were reconstructed in lung and mediastinal windows. High-resolution images were reconstructed at 1-mm collimation with 10-mm intervals. Two experienced radiologists independently evaluated each examination; disagreements were resolved by consensus. The prespecified findings were ground-glass opacity, interstitial thickening, pulmonary nodules, consolidation, fibrotic change, pleural effusion, and mediastinal lymphadenopathy. Terminology followed standard thoracic imaging definitions [18]. A participant was classified as having an abnormal CT if at least one prespecified abnormality was present. Statistical Analysis Analyses were performed in SPSS version 23.0 (IBM Corp., Armonk, NY, USA). Continuous variables are presented as mean ± standard deviation, and categorical variables as number and percentage. Continuous variables were compared using the independent-samples t test [19]. Categorical variables were compared using Pearson's chi-square test; Fisher's exact test was used when expected cell counts were small. Multivariable logistic regression was used to estimate adjusted odds ratios and 95% confidence intervals for abnormal CT findings [20,21]. Statistical significance was defined as a two-sided p value <0.05. Ethical Considerations The Institutional Ethics Committee approved the study. All participants provided written informed consent before enrollment.

Participant Characteristics

The study included 60 adults with type 2 diabetes mellitus. Their mean age was 54.2 ± 9.8 years, and 38 (63.3%) were men. The mean duration of diabetes was 8.7 ± 5.2 years, and the mean HbA1c was 8.4 ± 1.9%.

Distribution of CT Findings

Forty-eight participants (80.0%) had at least one abnormal chest CT finding. Ground-glass opacity was most common (45.0%), followed by interstitial thickening (33.3%), pulmonary nodules (25.0%), and fibrotic change (16.7%). Twelve participants (20.0%) had no abnormality (Table 1 and Figures 1 and 2). Because more than one finding could occur in the same participant, the percentages of individual abnormalities do not sum to 100%.

Table 1: Distribution of chest CT findings in the study population

Figure 1: Distribution of abnormal chest CT findings among 60 participants

Figure 2: Proportion of participants with normal and abnormal chest CT examinations

CT Findings and Glycemic Control

Thirty-nine participants had HbA1c ≥7%, and 21 had HbA1c <7%. Any abnormal CT finding was present in 35 of 39 participants (89.7%) with HbA1c ≥7% and 13 of 21 (61.9%) with HbA1c <7% (p=0.017). The individual patterns occurred more often in the higher-HbA1c group, but none reached statistical significance in the unadjusted categorical comparisons (Table 2). The mean HbA1c was higher among participants with an abnormal CT than among those with a normal CT (8.9 ± 1.8% vs 6.8 ± 1.2%; p<0.001).

Table 2: Chest CT findings according to glycemic control

Values are n (%). *Fisher's exact test; other p values are from Pearson's chi-square test.

CT Findings and Duration of Diabetes

Twenty-one participants had lived with diabetes for more than 10 years, and 39 had a duration of 10 years or less. Interstitial thickening (57.1% vs 20.5%; p=0.004), fibrotic change (33.3% vs 7.7%; p=0.025), and any abnormal CT finding (95.2% vs 71.8%; p=0.042) were more frequent in the longer-duration group. The difference in ground-glass opacity was close to, but did not meet, the prespecified significance threshold (61.9% vs 35.9%; p=0.053) (Table 3).

Table 3: Chest CT findings according to duration of diabetes

Values are n (%). *Fisher's exact test; other p values are from Pearson's chi-square test.

Predictors of Abnormal CT Findings

In the reported multivariable logistic regression model, HbA1c ≥7% was associated with higher odds of an abnormal CT finding (adjusted OR 4.82, 95% CI 1.52-15.28; p=0.008). Diabetes duration >10 years was also associated with abnormal CT findings (adjusted OR 3.67, 95% CI 1.18-11.42; p=0.025). Age >50 years and male sex were not statistically significant predictors (Table 4).

Table 4: Multivariable logistic regression for abnormal chest CT findings

CI, confidence interval; OR, odds ratio.

Table 5: Clinical variables according to chest CT status

Values are mean ± standard deviation or n (%).

Principal Findings Four of every five participants had at least one abnormal chest CT finding. Ground-glass opacity and interstitial thickening predominated, and one quarter of participants had pulmonary nodules. Abnormal CT findings were more frequent among participants with HbA1c ≥7% and among those with diabetes for more than 10 years. Longer diabetes duration was specifically associated with interstitial thickening and fibrotic change. These findings are consistent with the broader concept that the lung may be affected by chronic metabolic and microvascular injury in diabetes [4-6]. Comparison with Previous Evidence Earlier physiological studies documented altered lung elasticity and modest restrictive or diffusion abnormalities in diabetes [2,3,10,13]. Quantitative perfusion CT has demonstrated differences in pulmonary blood flow, blood volume, and permeability even when conventional high-resolution images show no overt disease [12]. More recent quantitative CT studies have reported measurable differences in fibrosis-related attenuation and pulmonary vascular indices in patients with type 2 diabetes and interstitial lung abnormalities [14,22]. The present study extends this literature by describing visually assessed CT patterns in a clinical sample from India, although its design does not establish that diabetes caused the observed abnormalities. Possible Mechanisms Persistent hyperglycemia can promote oxidative stress, endothelial dysfunction, advanced glycation, and inflammatory signaling [7-9]. Within the lung, these processes may alter the alveolar-capillary barrier and extracellular matrix, producing ground-glass attenuation or interstitial thickening before established fibrosis becomes apparent [6,26]. The higher prevalence of interstitial and fibrotic abnormalities in participants with longer diabetes duration is compatible with cumulative injury, but longitudinal imaging is required to confirm progression. Clinical Interpretation The association between CT abnormalities, HbA1c, and diabetes duration suggests that respiratory symptoms in patients with long-standing or poorly controlled diabetes should be evaluated carefully. Intensive glycemic control reduces established diabetic complications, but whether it changes pulmonary CT abnormalities remains uncertain [23,24]. The high prevalence reported here should not be interpreted as evidence for routine CT screening of asymptomatic patients. CT exposes patients to ionizing radiation, the study had no non-diabetic control group, and several findings are nonspecific. Imaging decisions should therefore be based on symptoms, examination, pulmonary function, and established clinical indications. Pulmonary nodules were found in 15 participants. Their clinical importance depends on nodule size, morphology, growth, smoking exposure, and other risk factors. Follow-up should use established incidental nodule guidelines rather than diabetes status alone [25]. Strengths and Limitations The study used a standardized CT protocol and independent assessment by two radiologists. It also evaluated associations with routinely available clinical markers. Several limitations affect interpretation. The cross-sectional design prevents temporal or causal conclusions. The small single-center sample limits precision and generalizability. A non-diabetic control group was not included, so the background prevalence of nonspecific CT findings cannot be estimated. Pulmonary function testing was not available for all participants, and quantitative CT analysis was not performed. Information on inter-reader agreement, recruitment method, smoking distribution, symptoms, and follow-up was insufficient for additional analysis. Finally, the multivariable model could not be independently verified without participant-level data.

Abnormal chest CT findings were common in this hospital-based sample of adults with type 2 diabetes mellitus. Any CT abnormality was associated with HbA1c ≥7%, while interstitial thickening and fibrotic change were more frequent after more than 10 years of diabetes. These results support prospective controlled studies that combine CT, pulmonary function testing, symptom assessment, and longitudinal follow-up. They do not establish a basis for routine CT screening in asymptomatic patients.

Acknowledgements

The authors thank the staff of the Departments of Radiodiagnosis and Endocrinology, the radiology technologists and nursing staff who supported data collection and CT examinations, and the patients who participated in the study.