Rigidity in Parkinson's disease.

Area of Science:

• Neurology
• Movement Disorders

Background:

• Rigidity is a key motor symptom in Parkinson's disease (PD), alongside bradykinesia and tremor.
• Despite its diagnostic importance, rigidity is less understood than other PD motor symptoms.
• Existing knowledge gaps exist in its phenomenology, neurophysiological basis, and treatment response.

Purpose of the Study:

• To critically review and clarify conceptual ambiguities surrounding rigidity in Parkinson's disease.
• To examine current assessment strategies, including clinical and instrumental approaches.
• To consolidate understanding of the pathophysiology of rigidity in PD.

Main Methods:

• Narrative review of existing literature.
• Analysis of conceptual definitions and clinical interpretations of rigidity.
• Comparison of clinical and instrumental assessment methods.
• Synthesis of molecular, neuroimaging, and neurophysiological findings.

Main Results:

• The term "rigidity" is inconsistently applied across fields, leading to clinical interpretation issues.
• Current assessment methods have distinct strengths and limitations for characterizing PD rigidity.
• Insights into rigidity's pathophysiology are emerging from various research domains.

Conclusions:

• Further research is needed to address the conceptual and methodological gaps in understanding PD rigidity.
• A clearer framework is required for consistent clinical assessment and targeted therapeutic development.
• This review provides a foundation for future research into Parkinson's disease rigidity.