Redefining Spasticity: The Spasticity X Working Group Consensus Statement.

Inconsistent and variably interpreted definitions of spasticity, alongside evolving mechanistic understanding, highlight the need for a clear, clinically relevant consensus definition. An international expert panel used a modified Delphi process to develop a concise, clinically applicable definition that reflects current understanding and supports consistent assessment and management. Participants reviewed existing definitions, completed a pre‑meeting survey, and engaged in structured discussions, with draft definitions iteratively refined through successive rounds of voting to achieve consensus. Key components identified included disordered sensorimotor control, central nervous system involvement, and velocity‑ and length‑dependent resistance to passive stretch, while existing definitions were considered either overly narrow or insufficiently relevant to clinical practice. The consensus definition characterizes spasticity as "A disorder of sensorimotor control resulting from upper motor neuron disease. It is characterized by velocity- and length-dependent involuntary muscle overactivity, which is intermittent or sustained, during passive stretch." This definition integrates contemporary mechanistic concepts with clinical applicability and is intended to improve conceptual clarity, facilitate communication, and promote consistency in diagnosis, measurement, and treatment.