Diffusion tensor imaging in idiopathic inflammatory myopathies: A case–control study

Objectives: It was aimed to assess the potential of diffusion tensor imaging (DTI) in detecting muscle inflammation in individuals affected by idiopathic inflammatory myopathies (IIM) compared to healthy controls. Specifically, we investigated the impact of myositis-related inflammation on the diffusion of water molecules across the sarcolemma and its detectability through DTI. Material and Methods: This prospective cross-sectional observational study included 36 patients diagnosed with IIM ([based on clinical tests manual muscle testing [MMT8] and serological marker N-acetyl-cystein(NAC)-activated creatine kinase [CPK-NAC]) and 51 healthy controls. All participants underwent bilateral thigh magnetic resonance imaging (MRI) with a DTI protocol. For patients, three region of interests (ROI) (80 mm 2 to 130 mm 2 ) were delineated on the most affected muscle containing maximum signal intensity (edema), while in controls, the ROIs were drawn on the healthy vastus lateralis muscle and average of five readings were used for statistical analysis. Average apparent diffusion coefficient (ADC) value, fractional anisotropy (FA), and three eigenvalues: Maximum (λ1), middle (λ2), and minimum (λ3) were measured in all the subjects. Results: The average age for cases and controls was 33.08 ± 12.45 years and 40.70 ± 17.17 years, respectively, with no significant age or gender distribution differences. MMT8 scores averaged 103.33 ± 36.42, and CPK-NAC values averaged 4323.44 ± 6354.45 U/L. DTI analysis revealed significantly higher average ADC values in patients (2.07 ± 0.45) compared to controls (1.76 ± 0.26) with a P < 0.001. FA values showed no significant difference (0.38 ± 0.19 in patients vs. 0.33 ± 0.09 in controls, P = 0.094). The three eigenvalues in the patients were 2.76 ± 0.63, 2.35 ± 0.33, and 1.30 ± 0.29, respectively, and in controls were 2.37 ± 0.36, 1.72 ± 0.25, and 1.21 ± 0.27, respectively, with P = 0.001, <0.001, and 0.818, respectively. Conclusion: In individuals with IIM, disruptions in the sarcolemma lead to altered water molecule diffusion, detectable through DTI. The study demonstrated significant differences in average DTI ADC, maximum (λ1), and middle (λ2) eigenvalues between cases and controls ( P < 0.001). Integrating DTI into routine myopathy MRI may enhance the differentiation between inflamed and normal muscles. Limitations included the absence of follow-up to observe treatment effects and the non-characterization of IIM into distinct subtypes.