Pathological Changes in Spastic Muscle Reflexes Evoked by Passive Stretch or Tendon Taps

Abstract

Spasticity is a motor disorder which occurs after CNS lesions. Although in diagnostic terms clinicians worldwide would largely agree over the term spasticity, no totally satisfying physiological definition has been agreed upon (see Thilmann, this volume). The most widely accepted definition is that of Lance (1980): ‘Spasticity is a motor disorder characterized by the velocity-dependent increase in tonic stretch reflexes (‘muscle tone’) with exaggerated tendon jerks, resulting from hyperexcitability of the stretch reflex as one component of the upper motor neurone syndrome.” This definition contains two assumptions: (a) spasticity is a disorder mainly affecting reflex systems, and (b) it is defined by a passive movement in which increased muscle tone correlates with the velocity of a passive muscle stretch. Implicitly it is often assumed that the disability of the patient is correlated to the degree of disturbance in reflexes and to muscle tone (for literature see Feldman et al. 1980). During voluntary activation of muscles, however, the disability may differ greatly from that seen during passive disturbance. This issue is discussed further in the chapters by Fellows et al. and Dewald and Rymer in this volume.