Abstract
Background. B mode ultrasound (US) and shear wave elastography (SWE) are easily accessible clinician lead imaging tools for idiopathic inflammatory myo¬pathies (IIM) but require further validation against standard diagnostic proce¬dures such as MRI and muscle biopsy. Our study aims to validate muscle B mode ultrasound (US) and shear wave elastography (SWE) in idiopathic inflammatory myopathies (IIM) against MRI and muscle biopsy findings.
Methods. In this prospective cross-sectional study, we compared US findings to MRI and muscle pathology in a group of 20 IIM patients seen in the clinic. US domains (echogenicity, fascial thickness, muscle bulk, shear wave speed and power doppler) in the deltoid and vastus lateralis were compared to MRI domains (muscle oedema, fatty infiltration, and atrophy) and muscle biopsy findings (in¬flammatory infiltrates, myonecrosis, atrophy and fibro-fatty infiltration) in the same muscle. A composite index score (1-4) was used as an arbitrary indicator of overall muscle pathology in biopsies.
Results. Increased echogenicity was significantly associated with the presence of fatty infiltration/atrophy on MRI (p=0.047) in the vastus lateralis and showed a non-significant association with muscle inflammation, myonecrosis, fibrosis, and fatty infiltration/atrophy (p>0.333). High echogenicity also had a non-significant association with a higher composite biopsy index score in the vastus lateralis (p=0.380). SWS and US measures of fascial thickness and muscle bulk showed poor discrimination in differentiating between pathologies on MRI or muscle biopsy. Power Doppler showed no statistical association with oedema on MRI or inflammation or fatty infiltration on biopsy. Overall, the US was very sensitive in detecting the presence of muscle pathology shown on MRI (67-100%) and showed reasonable specificity (75-100%). Increased echogenicity showed good sensitivity in detecting muscle pathology (83-100%) but lacked specificity in dif¬ferentiating pathological muscle changes specific to IIM (0%).
Conclusion. Our findings show that muscle echogenicity has a high sensitivity but low specificity for detecting muscle pathologies specific to IIM. Traditional visual grading scores are not IIM-specific and require further refinement and validation. Future studies should focus on developing a feasible scoring system that is reliable and allows translation to clinical practice.