Deep brain stimulation lead fracture with normal impedances: case report and review of literature.

Lead fracture is a well-acknowledged form of hardware failure in deep brain stimulation (DBS) implants, with an incidence ranging from 1.46 to 5%. It has been noted to occur more frequently in patients with dystonia, and in terms of location in the cervical region. Impedance measurements serve as an objective means to assess the integrity of a DBS system, with increased impedance values typically indicative of lead fracture. We report a case of normal measured impedances in the presence of complete lead fracture. A 12-year-old patient with a history of secondary dystonia due to cerebral palsy treated with GPi DBS (Boston Scientific®) presented in dystonic crisis. Upon initial review the DBS system was considered intact based on measured impedances within normal range. Following further exploration, a chest X-ray was performed that showed fracture and dislocation of both extension leads. Normal impedance values in a system cannot be relied upon to ensure system integrity. If the impedance values are out of range then the system integrity is compromised, but if the impedance values are within range the system integrity might still be compromised. It is crucial for clinicians to include this possibility in any patient presenting with subtherapeutic therapy or undergoing MRI scanning. Impedance measurements only may not provide a sufficient robust indication of system integrity in DBS implants, and in suspicion of a reduction in clinical effectiveness X-rays should also be performed to help establish system integrity.