Diffusion tensor imaging of vastus lateralis in patients with inflammatory myopathies

Inflammation in patients with myositis would increase diffusion of water molecules across sarcolemma that could be detected with the help of diffusion tensor imaging (DTI). We aimed to determine an association between DTI of vastus lateralis (VL) and histopathological findings in cases of myositis and to estimate diagnostic performance of different MRI variables in predicting histopathological outcomes.

This prospective cross-sectional observational study included 43 patients with myositis. MRI of bilateral thighs with DWI/DTI protocol was performed in all the patients. Thirty-three patients further underwent biopsy of right VL muscle. Imaging analysis included grading of 'muscle oedema' based on signal intensity (SI) and extent and 'fatty infiltration' based on extent on conventional sequences and, acquiring DWI and DTI parameters. Gold standard method to determine inflammation in muscles was histopathological examination. Comparison of DTI/DWI variables with clinical and histopathological variables was done.

The average DWI apparent diffusion coefficient (ADC) and DTI ADC values in the patients were 1.77 ± 0.35 and 2.06 ± 0.35, respectively. The average functional anisotropy (FA) was 0.39 ± 0.17 and, the three eigenvalues in the patients were 2.96 ± 0.63, 2.05 ± 0.32 and 1.20 ± 0.39, respectively. VL oedema SI weighted score was the best parameter for predicting effaced fascicular architecture and marked lymphocytic inflammation in endomysium on histopathology. VL fatty infiltration weighted score was the best parameter in predicting perifascicular atrophy.

Addition of DWI or DTI did not add significantly in determining active inflammation in cases of myositis.