The terminology of akinesia, bradykinesia and hypokinesia: Past, present and future

Akinesia, hypokinesia, and bradykinesia are extensively used to describe motor execution disturbances, but are applied inconsistently and cover more conditions than their Greek translations would suggest. We investigated the origins and changes in meaning of these terms over time, particularly in relation to Parkinson's disease (PD). We searched the literature from 1817 to 2015 for use and interpretation of the words akinesia, bradykinesia, hypokinesia, and PD. We found that akinesia and hypokinesia appeared as terms in the 19th century, opposite to hyperkinesia, but were used in the context of PD since 1920, while at the same time the 'bradykinetic syndrome' was introduced. Use of all terms increased in this period due to the encephalitis-lethargica-epidemic, and increased again with the discovery of levodopa from 1961. With the extensive use of criteria sets from the 1980s, bradykinesia replaced akinesia as the most commonly used term. The advent of the internet led to an increase in publications and an associated increase in heterogeneity in the use of the terms. This review shows the variation over time and the lack of unity in the terminology used to describe the range of movement execution disturbances. The current terminology fails to capture the nuances of the challenges we face in documenting these disturbances. We therefore recommend that the current situation may benefit from an objective and computationally solid approach using insights from network and circuitry technology and new developments in assessment technology. It is expected that this will contribute to a new framework for terminology in movement disorders.