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To the editor,

Spasticity is a disabling stroke complication. Despite the ascertained efficacy of botulinum toxin A (BoNT-A) in reducing spasticity, only few patients improve in upper limb active function and it is not possible on clinical basis to predict the response to treatment [1]. Motor-evoked potential (MEP) recording after transcranial magnetic stimulation (TMS) of motor cortex may provide noninvasive evaluation of central motor pathways [2]. We performed a prospective study in 14 chronic stroke patients with upper limb spasticity to assess the efficacy of TMS to predict upper limb functional response to one-time injections of BoNT-A. MEP findings were correlated with the change in the Action Research Arm Test (ARAT) score at one-month. Twelve patients (85·7%) had a reduction of spasticity and five of these patients (35·7%) also improved in the ARAT score. The presence of MEP in the affected hand had a positive predictive power of 57·1% and a negative predictive power of 85·7% of a functional improvement; thus, it is very unlikely that patients who have no MEP in affected hand respond to BoNT-A. These results confirm that BoNT-A reduces spasticity in stroke patients, and in some of them can also improve upper limb function. TMS may be useful in selecting the patients that are more likely to improve in upper limb function because it is more specific than clinic evaluation in assessing corticospinal pathway responsible for fine manipulatory finger movements [3].

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