Intraoperative evaluation

Introduction

As neuromodulation therapies become a treatment standard for a variety of disorders including medically refractory Parkinson's disease (PD), essential tremor, dystonia, pain syndromes, epilepsy, psychiatric disorders, and other future indications, more is being learned about the longevity and function of the implantable stimulator and its components. A literature review describes a 15%–30% failure rate that includes both infection and device failure [ ]. As neuromodulation becomes more prevalent due to increased disease penetration and as the number of medical conditions that are treatable with implantable neuromodulation devices increases, the total number of device failures will also rise. With this in mind, a systematic method for troubleshooting these failures is necessary in order to minimize both neuromodulation “downtime” and the number of invasive actions required to identify and replace failed components.

Surgery to isolate and fix device malfunctions takes time is expensive and exposes the patient to additional risk. Therefore, it is important to evaluate completely the patient who is responding poorly to neuromodulation before manipulating his/her device surgically. The potential causes of a poor response to neuromodulation include badly placed leads, an incorrect initial diagnosis, poor stimulator programming, and a worsening disease state [ ]. If specific symptoms or electrophysiological data derived through device interrogation do not suggest a device failure (see below), these clinical issues must be ruled out before assuming that a device malfunction exists. However, even when it is clear that a malfunction is present, it is essential to make every possible attempt to localize the fault noninvasively before embarking on surgical interventions.

Unless a failure mode, such as a lead fracture, is visible on X-ray, locating short or “open” circuits in system components is very difficult with current manufacturer-supplied hardware and software. Intermittent system problems are especially difficult to locate, and the differentiation of an intermittent problem from a pseudo problem can be nearly impossible.