The Role of Safe MRI in Diagnosing an Unusual Case of High‐Grade Glioma Adjacent to Globus Pallidus Interna DBS Electrode

Deep brain stimulation (DBS) is an established treatment for various movement disorders including genetic dystonias.1 DYT-1 dystonia, also known as DYT-TOR1A, is an autosomal dominant early-onset isolated dystonia usually presenting in childhood or adolescence.1 Medically refractory dystonia can be treated with DBS.1 The safety of MRI in DBS patients is often unclear to clinicians, and even if a system is MRI-compatible, acquiring MRI can still be difficult due to modifications required for MRI safety.2 Herein, we present rare case of high-grade glioma presenting adjacent to GPi-DBS electrode in a patient with chronic implantation for DYT-1 dystonia, which was poorly visualized on CT head and required an enhanced MRI brain for diagnosis. A 54-year-old woman with bilateral globus pallidus interna (GPi) deep brain stimulation (DBS) presented to hospital with right-sided hemiparesis. She had a history of DYT-1 dystonia that began as progressive generalized dystonia at the age of 8, involving the limbs and axial musculature. Due to medically refractory progressive dystonia, bilateral GPi-DBS electrodes were inserted at the age of 32 with significant improvement in symptoms. The Soletra implanted pulse generator (IPG) was switched to an Activa RC IPG in 2012, which was stable until 1 month before presentation when her IPG battery required replacement. She had a rechargeable Activa RC IPG implanted with no complications. Three weeks before presenting, she noticed mild right-sided weakness and increased dystonic posturing. Her symptoms worsened over 2 weeks and progressed to her right face. With attempts to increase stimulation, she experienced worsening truncal and gait instability, so stimulation was decreased. She then developed right-sided hemiparesis and presented to hospital. Her IPG settings showed normal impedances and stimulation currents. A CT angiogram head and neck was initially reported as normal. However, the profound deficits prompted an enhanced MRI brain, with slight protocol modifications including decreased number of FLAIR slices to prevent electrode overheating (i.e. SAR limit in vendor guidelines). MRI brain (Fig. 1) showed a poorly enhancing FLAIR signal abnormality extending from the left globus pallidus inferiorly into the pons, with asymmetric left cerebral peduncle enlargement (Fig. 1B). Brain biopsy of the lesion was completed, demonstrating high-grade glioma (WHO grade 3, IDH1 R132H negative, BRAF negative). The patient was treated with dexamethasone, temozolomide and 6 weeks of radiation. Due to significant progression and poor prognosis, she was transitioned to palliative care. Estimates show that more than 230,000 patients have received DBS worldwide,3 and 70% will require MRI within 10 years of implantation.4 Tagliati et al. found that, due to concerns over risks of MR imaging, less than half of centers surveyed performed brain MRI on DBS patients,5 although this has likely increased in recent years. In this case, without MRI, the diagnosis would likely have been missed and proper treatment may not have been initiated. With DBS systems, the main risk of MRI is heating at the electrode tip, which may potentially cause damage to surrounding brain tissue.2, 6 With modern DBS, there have been no known adverse events when the MRI protocols following the vendor guidelines.6 However, clinical protocols generally need to be adapted to follow these guidelines. Furthermore, MR safety contradictions between MR vendor and DBS vendors were recently highlighted, further complicating this issue.2 While vendor guidelines are restrictive, we show that only minor modification to routine protocols were required. With recent guideline modifications now including a novel less restrictive measure of heating (B1 + rms), more MRI sequences can be performed with only minor modifications to the routine clinical protocols. Hence, these cases should be discussed with radiologists rather than denying the test. This is one of the few reported cases of high-grade glioma spatially associated with a DBS electrode.7 One case of piloastrocytoma7 and two cases of high-grade glioma7, 8 have been reported immediately adjacent to DBS leads. Since most patients with DBS for Parkinson's disease pass away within two decades of implantation, genetic dystonia patients with DBS from young age have longer stimulation exposure, which raises the possibility of an increased risk of adverse effects to chronic stimulation. There is in-vivo evidence from animal studies that DBS can induce anti-apoptotic effects,9 and that synaptic and electrical integration of active neural networks into gliomas promotes tumor progression.10 However, the rare incidence of brain neoplasms in chronic DBS patients makes an association difficult to ascertain, and further observational studies as dystonia DBS patients continue to age is needed. Hence, although the few reports of tumors spatially associated with DBS electrodes have been mostly high-grade gliomas, association between the two remains unknown.7, 8 This case serves as one of the few documented observations to date. In summary, this case provides an important experience for other centers in safely using MRI in DBS patients without complications, and demonstrates a rare presentation of high-grade glioma in a chronic DBS patient. (1) Research project: A. Conception, B. Organization, C. Execution; (2) Analysis: A. Design, B. Execution, C. Review and Critique; (3) Manuscript: A. Writing of the first draft, B. Review and Critique. AB: 1C, 2A, 2B, 3A. ABo: 1C, 2A, 2B, 3A, 3B. AV: 1C, 2C, 3B. JG: 1C, 2B. IC: 1A, 2C, 3B. DM: 1A, 2C, 3B. RM: 1A, 2C, 3B. AF: 1A, 2C, 3B. SK: 1A, 1B, 2C, 3B. AL: 1A, 1B, 2C, 3B. We confirm that we have read the Journal's position on issues involved in ethical publication and affirm that this work is consistent with those guidelines. The authors confirm that the approval of an institutional review board was not required for this work. Informed consent was obtained for this case report. No specific funding was received for this work. The authors declare that there are no conflicts of interest relevant to this work. Arjun Balachandar, Alexandre Boutet, Artur Vetkas, Jurgen Germann, Ian Y. M. Chan, David Mikulis and Renato P. Munhoz report no fundings sources in the past 12 months. Andres M. Lozano and Alfonso Fasano received honoraria and/or research support from Abbott, Insightec, Boston Scientific, and Medtronic. Suneil K. Kalia received grants/grants pending from CIHR, and received payment for lectures including service on speakers bureaus from Medtronic.