Botulinum toxin type A versus phenol. A clinical and neurophysiological study in the treatment of ankle clonus

Aim. To reduce ankle clonus in patients with spastic paresis either phenol nerve block of the tibialis posterior nerve or botulinum toxin type A (BTA) injection in triceps surae muscles can be used. This study aims to compare the efficacy over time of phenol nerve block and BTA injection in the inhibition of ankle clonus. Methods. Twenty-two patients with spastic paresis presenting with ankle clonus were randomly treated with phenol nerve block of the tibialis posterior nerve or BTA injection in triceps surae muscles. Ankle passive dorsiflexion, clonus, M and H responses and H/M ratio were measured in all patients prior to treatment and 15 days afterwards, as well as one, three and six months later in 12 patients. Patient satisfaction was also recorded. Results. Both patient groups showed significant clonus reduction over time with the effect of phenol being greater than that of BTA. In one month, the degree of passive dorsiflexion significantly increased in both groups without any significant difference between them. H/M ratio reduced after phenol treatment and remained almost constant during the following six months, whereas it remained at baseline level after BTA treatment. Conclusion. While both treatments led to reduction in ankle clonus, phenol showed greater clinical efficacy. The difference in the neurophysiological results suggests that the two drugs have different action mechanisms with a more prevalent reduction of alpha motoneuron excitability in phenol-treated patients.