Are we underestimating the clinical efficacy of botulinum toxin (type A)? Quantifying changes in spasticity,strength and upper limb function after injections of Botox® to the elbow flexors in a unilateral stroke population

Abstract

Objective: To quantify the clinical efficacy of botulinum toxin type A in treating elbow flexor spasticity in a unilateral stroke population. Location: A spasticity clinic at a regional neurological rehabilitation centre.

Study design: A convenience sample longitudinal study. Fourteen subjects with elbow flexor spasticity secondary to a stroke were recruited. Two repeated measures, one before and another four weeks after treatment, were taken to quantify clinical efficacy.

Outcome measures: Elbow flexor spasticity was simultaneously rated with the modified Ashworth scale (MAS) and quantified by measuring the surface EMG from the flexors using a custom-built device. Strength at the elbow (isometric), grip strength and upper limb function (Action Research Arm test) were also assessed.

Treatment: Injections of botulinum toxin type A (Botox^®) to the m.biceps brachii (mean dose 70 U), m.brachioradialis (mean dose 56.5 U) and m.flexor digitorum longus (mean dose 83.3 U).

Results: Following treatment, spasticity (as measured by flexor EMG activity) reduced but the MAS was unable to detect this improvement. In some subjects, isometric flexor strength at the elbow as well as grip strength increased. This was contrary to the expected weakening following treatment with botulinum toxin type A and suggests an optimization of motor control.

Conclusion: Treatment with Botox^® reduces spasticity but does not necessarily cause a reduction in the force generating capabilities at the joint. The improvement in strength may have contributed to the improvements in upper limb function. The MAS is an inappropriate measure of spasticity.

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