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

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 a 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 a motor neurone excitability, although it is not linear. This suggests that the MAS measures muscle hypertonia rather than spasticity.