Disclosures: Dylan J. Lewis, DO: No financial relationships or conflicts of interest

Case Diagnosis: Grouped Discharges on EMG Associated with Implanted Stimulators

Case Description: A 47-year-old female with a history of C5-C6 decompression and fusion, left ulnar nerve transposition and gastric, vagal nerve and bladder stimulators was referred for electrodiagnostic testing of her upper limbs for numbness and tingling. Given the patient’s comorbidities as well as insulin pump-dependent diabetes mellitus, hypothyroidism, and the implanted stimulators for autonomic neuropathy, this patient was referred for electrodiagnostic testing. Routine upper limb nerve conduction studies demonstrated a mild right median neuropathy at the wrist. During needle EMG, the right upper limb was normal. While the reference electrode was still on the right hand, the monopolar needle was introduced into the left first dorsal interossei and 0.5-second-long repetitive burst discharges were observed with a firing frequency of about 1 Hz. These discharges were perfectly regular in frequency and duration. Because of the patient’s history of left ulnar transposition and the relative narrow differential of grouped discharges, myokymia was considered. However, upon moving the reference electrode to the ipsilateral limb, the group discharges ceased. Since multiple sources, pathological and artifactual, could produce grouped discharges, further chart and literature reviews were performed.

Setting: Outpatient ClinicAssessment/

Results: The literature and chart reviews demonstrated that the discharges seen in our patient most likely have the electromyographic signature of one of the implanted stimulator devices.

Discussion: Over the past decade, healthcare providers and electrodiagnostic labs are seeing more implantable devices such as gastric, bladder, deep brain, vagal nerve, and spinal cord stimulators. A knowledge of their typical discharge patterns, waveforms, and occasions when their signals may be observed is essential to distinguish from pathological causes of grouped discharges.

Conclusion: Given the increasing prevalence of implanted stimulator devices, physicians performing EMG should be familiar with their electromyographic waveforms to avoid misdiagnosis.

Level of Evidence: Level V

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PM&R Meeting Abstracts - https://pmrjabstracts.org/abstract/grouped-discharges-associated-with-implanted-stimulators-during-a-routine-emg-a-case-report/