Comparing the two-axis classifications of hyperkinetic disorders

Area of Science:

• Neurology
• Movement Disorders
• Classification Systems

Background:

• Hyperkinetic disorders encompass a range of conditions characterized by excessive involuntary movements.
• Existing classification systems for these disorders have evolved, with specific systems developed for dystonia, tremor, and myoclonus.
• These systems utilize a two-axis structure, generally differentiating between clinical characteristics and etiology.

Purpose of the Study:

• To analyze and compare the structure and content of two-axis classification systems for hyperkinetic disorders.
• To identify variations in the categorization of clinical features, neurophysiology, etiology, and other diagnostic tools across different disorder-specific classifications.
• To highlight the unique aspects of classifying dystonia, tremor, and myoclonus within a standardized framework.

Main Methods:

• Review of existing literature and classification systems for dystonia (2013, revised 2025), tremor (2018), and myoclonus (2025).
• Comparative analysis of the two-axis structure (Axis I: clinical, Axis II: etiology) across these classifications.
• Examination of the placement of neurophysiology, neuroimaging, genetic testing, and functional neurological disorders within the classification frameworks.

Main Results:

• All classifications use Axis I for clinical characteristics and Axis II for etiology, with myoclonus also having an Axis Ib for neurophysiology.
• Neurophysiology is integrated into Axis I for tremor and myoclonus, unlike dystonia where it's primarily Axis II.
• The placement of neuroimaging, genetic testing, and functional neurological disorders varies significantly across the classifications, reflecting disorder-specific diagnostic priorities.

Conclusions:

• The classification of hyperkinetic disorders, while sharing a common two-axis structure, demonstrates significant specificity in how different disorders are categorized.
• Variations in the inclusion and positioning of neurophysiological data and other diagnostic modalities underscore the unique characteristics of dystonia, tremor, and myoclonus.
• These classification exercises are crucial for standardizing the diagnosis and understanding of hyperkinetic movement disorders.