POS0814 DIAPHRAGMATIC MUSCLE THICKNESS – A POSSIBLE NEW TOOL IN ASSESSING LUNG INVOLVEMENT IN SYSTEMIC SCLEROSIS PATIENTS
Authors: C. Cobilinschi, E. Icatoiu, I. Săulescu, L. M. Groșeanu, D. Opriș-Belinski, A. Bălănescu, S. Caraiola, A. Bobirca, C. Jurcut, E. Moisa, S. Constantinescu, R. Dumitru
Journal: Annals of the Rheumatic Diseases (2024)

<h3>Background:</h3> Lung involvement remains one of the main targets of experts' efforts for detection and treatment since interstitial lung disease (ILD) is the main cause of mortality in systemic sclerosis (SSc). Despite suggestive interstitial changes detected in over 80% of SSc patients on high-resolution computed tomography (HRCT), only a third of patients are clinically overt for ILD. The diaphragm muscle has so far been overlooked as to its role in the respiratory impairment in SSc patients. The latter can exhibit diaphragmatic dysfunction due to a number of factors, namely increased airway resistance, disease-related sarcopenia, glucocorticoid use. <h3>Objectives:</h3> The aim of this study was to evaluate the impact of systemic disease on computed tomography (CT)-measured diaphragm thickness in patients with SSc with confirmed ILD. <h3>Methods:</h3> A multicentric, retrospective study was performed. We identified scleroderma patients with ILD and follow-up thoracic CT in the last three years. CT diaphragmatic thickness measurements were performed by two independent radiologists. The celiac axis was used as a reference point. At this level, diaphragm muscle thickness was measured on axial as well as coronal images. Mean obtained values and differences were used for the final analysis. Demographic data, clinical and laboratory parameters were collected from electronic patient records. The control group had a CT scan performed for a different pathology. Overlap syndromes, cachexia, neoplastic patients and chronic glucocorticoid users were excluded. <h3>Results:</h3> The study included 69 SSc patients (36 with diffuse SSc; 33 with limited SSc) with confirmed ILD and 92 age and gender-matched controls with no previous history of pulmonary diseases. SSc included 60 females and 9 males, with a mean age of 58.9 ±11.75 and controls were 76 females, 16 males, aged 57.59±10.26. Mean time from diagnosis was 7.48 years. Mean BMI was 23.01 kg/m<sup>2</sup>, total serum protein levels were normal (7.21g/dl) as well as muscle enzymes values. Almost half of SSc patients (37) had lower FVC (62.92%) and 41 patients presented reduced values of DLCO (60.54%);18 patients were suspected of pulmonary hypertension at cardiac ultrasound (mean PAPs =49.5mmHg). The 6MWT was less performant in 22 patients. The right hemidiaphragm (RD) thickness in the disease group measured 3.2mm±1.08 and the left(LD) 2.97mm±1.03 which was not significantly different from the control group (RD 3.51mm ±1.04;LD 3.43mm±0.96)(p=0.67). However, the RD thickness was significantly lower in SSc patients with lower FVC (p&lt;0.05), indicating a potential concomitant involvement of diaphragmatic muscle in ILD-SSc patients. We also performed a cross-tabulation plus Chi-square analysis and Mantel-Haenszl test. The odds ratio value was similar to that from binary logistic regression (OR=3.11). Thus, gender and age do not have important effects on the predictive value for the chosen muscle thickness cut-off. No significant difference was identified in CT-measured diaphragm thickness regarding the autoantibody profile, skin extension or other organ involvement (gastrointestinal tract, heart or kidney). Moreover, the diaphragm thickness does not appear to change according to disease duration (p=0.082). The variable of interest is non-dependent on immunosuppressive or antifibrotic agents. <h3>Conclusion:</h3> To our knowledge, this study is one of the very few to use CT-measured thickness of the diaphragm in SSc patients. The study suggests that diaphragmatic morphological changes may occur in SSc with lung involvement and lower FVC. Further diaphragmatic functional studies are required for the complete evaluation of the role of diaphragm in the pathogenesis of ILD-related SSc. <h3>REFERENCES:</h3> [1] Mirea, L., Cobilinschi, C., Ungureanu, R., Cotae, A. M., <i>et al.</i>, <i>A Trend towards Diaphragmatic Muscle Waste after Invasive Mechanical Ventilation in Multiple Trauma Patients-What to Expect?</i> J. Clin. Med. 2023; <b>12</b>(9): [2] Yakut, H. et al, <i>Assessment of diaphragmatic function by ultrasonography in patients with systemic sclerosis and its relation to clinical parameters: A case-control study</i> Wien. Klin. Wochenschr. 2023; <b>135</b>(19–20): 528–537. <h3>Acknowledgements:</h3> <b>NIL.</b> <h3>Disclosure of Interests:</h3> <b>None declared.</b>