Citation

Ramanathan V, Baskar D, Pari H. Ann. Indian Acad. Neurol. 2022; 25(3): 517-519.

Copyright

(Copyright © 2022, Medknow Publications)

DOI

10.4103/aian.aian_817_21

PMID

35936584

PMCID

PMC9350785

Abstract

The distinction between velocity dependence of spasticity from the other characteristic feature of spasticity, namely, the clasp knife phenomenon, is often not stated clearly or quickly discerned. While the lengthening reaction can be easily grasped with the analogy of a clasp knife, velocity dependence lacks an analogy. The underlying neural mechanisms between these two characteristics are different [Figure 1]. Hence, we wish to suggest a car seatbelt as an analogy, so that "velocity dependence" can be easily appreciated.

Several analogies are used to describe hypertonic states [Figure 1], which include spasticity, rigidity, and the less common paratonia. Based on certain key features, spasticity can be easily differentiated from rigidity at the bedside. Rigidity is a nonselective increase in the tone of agonist and antagonist without velocity dependence, and the increased tone remains uniform throughout the range of movement. On the contrary, spasticity is a velocity-dependent increase in tone resulting from the hyperexcitability of stretch reflexes.[1] It primarily involves the antigravity muscles - flexors of the upper limb and extensors of the lower limb. During the passive stretch, a brief "free interval" is appreciated in spasticity but not in rigidity because the resting muscle is electromyographically silent in spasticity. In contrast, in rigidity, the resting muscle shows firing...

Language: en