Letter to editor in response to De vloo et al.: Open fracture of DBS leads with normal electrical impedance

We here add a similar case to the report by Drs. DeVloo, Vermeulen, Vandenberghe and Nuttin [[1]DeVloo P. Vermeulen L. Vandenberghe W. Nuttin B. Open fracture of deep brain stimulation leads with normal electrical impedances.Brain Stim. 2020; 13: 1639-1641https://doi.org/10.1016/j.brs.2020.09.018Abstract Full Text Full Text PDF PubMed Scopus (3) Google Scholar], describing a patient with intact impedance measures despite an internal breakage of a deep brain stimulator (DBS) extension. Our male patient underwent subthalamic (STN) DBS for advanced Parkinson’s disease (PD) in 2004 at the age of 48 (3389 leads connected to two 7482A-51 extensions, Kinetra, Medtronic Inc, Minneapolis MN). He underwent several pulse generator replacements (later in 2004 after a lightning strike, then for battery depletions in 2009, 2014, and with a rechargeable Activa RC in 2017). His PD progressed, especially in his right body with significant dystonia in his hand, requiring joint fusions. His gait was most affected, but he was able to ambulate around his home with a walker. He had difficulty tolerating PD medications due to dyskinesia, but started taking 4 tablets of levodopa/benserazide (50/12.5 mg) daily in 2018 in addition to amantadine for symptom management. In 2020 at the age of 64, he developed shocks in his head/neck, both spontaneously and sometimes with neck movements. Impedances of all DBS leads were completely normal and unchanged from measurements obtained at previous annual check-ups. Notably, the impedances were different in the right and left leads (Fig. 1A), and remained the same with his head turned to different positions. Skull and neck radiography revealed an apparent wire disconnection in the left DBS extension (Fig. 1B). While he had not had skull radiography since his original surgery, chest radiography showing the extension coming down from the neck to the pulse generator indicated that this breakage was present for at least one year prior (Fig. 1C). Based on his clinical picture we wondered how long this may have been an issue, but not identified due to normal impedance measures. The patient underwent revision of his extension and intra-operative findings showed a physically intact extension cable with the wiring within the extension being pale and seemingly having lost its coil (Fig. 1D). Post-operative course was marked by worsening of gait, such that he required gradual adjustment in stimulation parameters, medications, and botulinum toxin injections over 2 weeks in hospital, to regain his ability to walk with a walker. It is not clear how normal impedances could be measured using the clinician programmer (N’Vision Clinician Programmer model 8840 and CT900D Clinician tablet) with such apparent wire disconnection. Possibly the intact external insulation of the silastic cover of the extension could allow these measurements to be obtained. Regardless, it is a concerning problem with long term DBS. This case further emphasizes the need to use radiography to check connections in advanced PD patients, especially those having falls, even with normal impedance measurements. No specific funding for this case report.

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