Risk factors for unpleasant paresthesiae induced by paresthesiae-producing deep brain stimulation.

Paresthesiae-producing deep brain stimulation (stimulation of ventrocaudal nucleus-VC, medial lemniscus-ML or internal capsule-IC) is one of the few procedures to treat the steady element of neural injury pain (NIP) currently available. Reviewing the first 60 patients with NIP submitted to deep brain stimulation (DBS) from 1978 to 1991 at the Division of Neurosurgery, Toronto Hospital, University of Toronto, we observed that 6 patients complained of unpleasant paresthesiae with paresthesiae-producing DBS, preventing permanent electrode implantation in all of them. Such patients accounted for 15% of the failures (6 out of 40 failures) in our series. In an attempt to improve patient selection, we reviewed our patients considering a number of parameters in order to determine risk factors for unpleasant paresthesiae elicited by paresthesiae-producing DBS. The results showed that this response happened only in patients with brain central pain complaining of evoked pain, secondary to a supratentorial lesion. Age, sex, duration of pain, quality of the steady pain, size of the causative lesion and site (VC,ML,IC) and type (micro or macroelectrode) of surgical exploration were not important factors. Unpleasant parethesiae in response to dorsal column stimulation, restricted thalamic lesion on computed tomography and the occurrence of associated intermittent pain were considered major risk factors in this subset of patients and the presence of cold allodynia or hyperpathia in isolation and the absence of sensory loss were considered minor risk factors. It is our hope that the criteria here established will improve patient selection and so, the overall results of DBS.