Changes in muscle elasticity are expected in patients with untreated myositis. 
The purpose of this study was to define the accuracy of shear-wave elastography 
(SWE) in diagnosing myositis. This case control study included 21 patients (mean 
age, 49.4 y; 12 women) with myositis who underwent SWE, magnetic resonance 
imaging (MRI) and biopsy of the involved muscle group. SWE was performed 
accordingly in a control group (n = 24; mean age, 51.2 y; 8 women). Blood tests 
consisted of creatine kinase (CK) and aldolase. Two operators performed SWE in 
longitudinal and transverse planes of muscular fibers, quantifying the mean 
shear-wave velocity (SWV) and the pattern of stiffness. On MRI, short-TI 
inversion recovery (STIR) signal hyperintensity and T1 contrast enhancement of 
muscle was considered diagnostic for myositis. The patient group suffered from 
different types of myositis (nine patients with polymyositis, eight with 
dermatomyositis and four with other types of myositis). Blood tests showed 
significantly increased CK and aldolase values in patients with myositis (p < 
0.001 and p < 0.0001). MRI showed a sensitivity of 0.95. In the patient group, 
the mean SWVs of longitudinal and transverse measurements were 2.8 ± 1.4 m/s and 
3.1 ± 1.2 m/s, respectively. In the control group, SWVs were 2.3 ± 0.5 m/s and 
2.4 ± 0.5 m/s, respectively. The difference between transverse measurements was 
significant (p = 0.02). Increased heterogeneity as a marker for myositis in 
transverse SWE showed a sensitivity of 0.8, specificity of 0.79, positive 
predictive value (PPV) of 0.76 and negative predictive value (NPV) of 0.82. 
Inter-observer difference was very low (κ = 0.92). Increased heterogeneity in 
both planes compared with histologic results showed a sensitivity of 0.56, 
specificity of 0.93, PPV of 0.91 and NPV of 0.62. Spearman correlation between 
CK <1000 U/L and SWE was 0.54. In conclusion, transverse orientation SWE may 
serve as an imaging biomarker for the diagnosis of myositis through the display 
of a heterogeneous pattern and increased absolute SWV values of inflamed 
muscles.