Ultrasound elastography in the assessment of rigidity in Parkinson's disease: A scoping review

In individuals with Parkinson's disease (PD), rigidity is a form of muscle hypertonia which manifests as muscular stiffness, leading to altered mechanical properties of muscle tissue. Ultrasound elastography (UE) is an emerging diagnostic imaging technology that can assess muscle stiffness. This scoping review aims to evaluate the current literature on muscular rigidity in PD as measured by UE, examine existing UE assessment methodologies, and propose future directions when measuring muscular rigidity in PD using UE.

This scoping review was conducted following specific guidelines and searching these databases: Scopus, PubMed, Web of Science Core Collection, MEDLINE and CINAHL Ultimate.

Ten studies were included after screening, using either strain elastography (SE) or shear wave elastography (SWE) to measure muscular rigidity in PD. Muscular rigidity was typically greater in individuals with PD compared to controls, with minimal bilateral differences within PD patients. UE-derived muscular rigidity was associated with clinical manifestations of PD, and rigidity was influenced by joint angle, medications, and therapeutic interventions. However, the included studies assessed rigidity using a wide range of methodologies (e.g., protocol design, system specification, and acquisition methods), which restricts comparability.

UE demonstrates strong potential as a non-invasive tool for quantifying muscular rigidity in PD, which is increased in these patients. Nevertheless, small sample sizes and inconsistent methodologies undermine definitive conclusions. Future studies should adhere to the methodological recommendations outlined in this review, including the adoption of standardised protocols, larger sample sizes, and robust longitudinal and reliability designs.