Spasticity Part 2

What is spasticity?

Despite many years of debate and investigation there is still no agreement about just what spasticity is, nor a clear understanding of the underlying cause/s of spasticity.  This lack of agreement is shown by the multiple definitions reported in the literature (see Ibuki & Bernhardt 2007 for a review; van den Noort et al 2017 for an overview of the problem with suggested solutions for clinicians and researchers).

There is one clear and unambiguous definition of spasticity from a neurological convention held in 1980 (Lance 1980).  This definition is:

“a motor disorder characterized by a velocity dependent increase in the tonic stretch reflex (muscle tone) with exaggerated tendon jerks, resulting from hyper excitability of the stretch reflex, as one component of the upper motor neurone syndrome.”

What does this mean?  It means that if spasticity is present in a muscle, for example in the elbow flexors, when the elbow is (passively) extended slowly there is no response from the muscle and the elbow joint will extend without the muscle responding to the imposed stretch.  However, if the elbow is (passively) extended rapidly the elbow flexor muscles will respond to the imposed stretch and contract or “catch”, stopping the smooth extension.  The video on the right demonstrates this response to stretch clearly.

This definition describes spasticity as a peripheral response to an imposed rapid stretch. This peripheral response of a muscle to an externally imposed stretch does not necessarily prevent active movement as shown in the same video where the person is able to actively flex and extend their elbow.

Spasticity, using the Lance definition, may develop as a secondary consequence after a stroke over a number of months.

Using the 1980 definition, spasticity is a specific characteristic of a muscle’s response to an imposed stretch which can be clearly demonstrated and importantly, measured.  The Tardieu scale (Tardieu et al 1954) has been shown to distinguish between this peripheral neural response of the muscle to stretch and the mechanical properties of the muscle (eg muscle stiffness).  In contrast, the commonly used Ashworth Scale does not distinguish between the neural and mechanical properties of a muscle and consequently overestimates the incidence of spasticity (Patrick & Ada 2006).

However, despite the fact that the Lance definition provides a clear clinical test of spasticity, researchers have problems with the underlying assumptions of this definition (see Pandyan et al 2005).  The next blog will consider a proposed alternative to the Lance definition of spasticity.  The blog will also consider the limitations of this alternative definition when making clinical decisions.

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