A phenomenological approach to spastic movement disorders: an international expert panel consensus

Background and objectives: Hyperkinetic movement disorders, characterized by complex and overlapping motor patterns, present significant challenges in classification and treatment. The inconsistency in definitions and descriptors complicates both research and clinical communication. This study aims to provide an overview of current terminology and definitions related to spasticity and other hyperkinetic movement disorders associated with central nervous system lesions. We propose a unified terminology and classification system for spastic movement disorders (SMD). Methods: In this scoping review, definitions of spasticity, dystonia, tremor, chorea, hemiballismus, athetosis, myoclonus, and dyssynergia were reviewed, with emphasis on overlaps and diagnostic challenges among these disorders. The goal was to develop a consensus expert opinion on a phenomenological approach to SMD. Results: The proposed classification system for spasticity includes clinical characteristics (Axis 1) and etiology (Axis 2). Axis 1 includes: age at onset, body distribution, disease course, phenomenological description, and impact on body function, activity, and participation. The phenomenological description allows sub-classification of SMD into: phasic reflex overactivity, stimulus-induced muscle overactivity, constant muscle overactivity, and lack of muscle selectivity. These categories clarify disabling phenotypes such as clonus, dysregulated co-contraction, muscle spasms, activity-induced muscle hypertonia, associated reactions, and persistent muscle hypertonia. Discussion: This framework for classification of SMD aims to establish a common language for describing clinical phenotypes. By adopting a phenomenological approach, we underscore the importance of consistent descriptors and propose a systematic classification method for movement disorders, particularly spasticity. We hope this unified terminology will enhance clinical practice, research, and ultimately, patient care.