Introduction: Deep brain stimulation (DBS) provides an effective and durable treatment for a variety of neurologic conditions. Though infrequent, DBS malfunction is somtimes observed without an obvious radiographic abnormality. We suggest the possibility of lead malfunction occuring in radiographic continuity as a consequence of mechanical stress prior to overt failure.
Methods: Since 1997 our institution has implanted over 1100 DBS electrodes and accumulated significant experience in follow up of our patients and outside referrals. Over time we noted areas of apparent stress along the DBS electrode (Fig. 1) without apparent malfunction. A single case crystallized our previously random observations.
Results: A masterfully placed DBS system seven years post implant from an outside high volume center presented with progressive therapeutic failure and erratic changes in impedence without radiographic evidence of fracture (Fig. 2). During revision of the DBS electrodes the suture at the junction of the lead and extension kit was found to have cut through the insulating boot and completely eroded the insulating material of the electrode revealing bare wire. This area of suture cut through has been noted on other cases (Fig. 3) but never to the degree of actually eroding the insulation of the electrode although deformation of the underlying lead has been appreciated (Fig. 4).
Conclusions: 1. DBS lead malfunction may occur without obvious radiographic abnormality. 2. DBS lead malfunction may occur secondary to mechanical stresses. 3. Our observations suggest three particular areas of predictable mechanical stress. 4. With time and increased utilization of DBS, it is likely that "low frequency/rare" malfunctions may become more common.
Patient Care: 1. Recognizing the potential that DBS lead malfunction may occur without overt lead seperation. 2. Suggesting probable sites of mechanical compromise of DBS leads.
Learning Objectives: 1. Consideration of a potential for DBS lead failure "in continuity". 2. Recognizing DBS malfunction may occur along a spectrum of varying degrees of impedence change and unusual features prior to complete failure (Fig. 5).