SHORT REPORT

The relation between Ashworth scale scores and the excitability of the motor neurones in patients with post-stroke muscle spasticity

A M O Bakheit¹, V A Maynard², J Curnow³, N Hudson⁴ and S Kodapala⁴

¹ Peninsula Medical School and Plymouth Primary Care Trust, Plymouth, UK
² Institute of Health Studies, University of Plymouth
³ Department of Medical Physics, Derriford Hospital, Plymouth
⁴ Department of Neurophysiology, Derriford Hospital, Plymouth

Correspondence to:
Correspondence to:
Professor Magid Bakheit, Beauchamp Centre, Mount Gould Hospital, Plymouth PL4 7QD, UK;
magid.bakheit{at}pcs-tr.swest.nhs.uk

Background: The modified Ashworth scale (MAS) is the most widely used method for assessing muscle spasticity in clinical practice and research. However, the validity of this scale has been challenged.

Objectives: To compare the MAS with objective neurophysiological tests of spasticity.

Methods: The MAS was recorded in patients with post-stroke lower limb muscle spasticity and correlated with the excitability of the motor neurones. The latter was evaluated by measuring the latency of the Hoffmann reflex (H reflex) and the ratio of the amplitude of the maximum H reflex (H_max) to that of the compound action motor potential of the soleus muscle (M_max).

Results: Data on 24 randomly recruited patients were analysed. Patients were divided into two groups according to their MAS score: 14 had a MAS score of 1 (group A) and 10 scored 2 (group B). The two groups were comparable with respect to age and sex, but in group A there was a longer period since the stroke. The H reflex latency was reduced and the H_max:M_max ratio was increased in both groups. The H_max:M_max ratio values were higher for group B but the differences were not statistically significant.

Conclusions: There is a relation between the MAS scores and motor neurone excitability, although it is not linear. This suggests that the MAS measures muscle hypertonia rather than spasticity.

Keywords: Ashworth scale; motor neurone; spasticity

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