Patient Safety: Considerations When Performing an EMG/NCS on a Patient with a Spinal Cord Simulator

A physician receives a referral to perform an EMG/NCS on a patient with a spinal cord stimulator. The physician wants to ensure that the appropriate precautions are taken to safely proceed with the EMG/NCS.

Question: A patient is referred for an EMG/NCS that has a spinal cord stimulator (SCS) to treat pain from a chronic lumbar radiculopathy. It is considered safe to proceed with electrodiagnostic testing when which of the following pre-procedure tasks are completed?

A. Review available imaging to determine the location of the SCS leads and pulse generator

B. The SCS is turned off

C. It is verified that patient has a fully implanted SCS with internalized leads and pulse generator, and they are not undergoing an SCS trial with leads exiting the skin connecting to an external pulse generator.

D. All of the above

Explanation:

The correct answer is D.

A spinal cord stimulator (SCS) is a device implanted into the epidural space to treat chronic neuropathic pain. It consists of epidural leads connected to a pulse generator that contains the battery and programmable elements of the system. Patients typically undergo a 3-8 day trial where temporary SCS leads are placed in the epidural space, and these leads exit through the skin to connect to an external pulse generator. If the patient receives satisfactory pain relief from the trial, they will often proceed with surgical implantation [1].

For painful conditions of the lumbar spine and lower extremities, the leads are placed in posterior epidural space of the thoracic spine and are tunneled under the skin to connect to a pulse generator that is commonly placed subcutaneously in the upper buttock, lateral hip, or abdominal regions. It is important to be aware of the lead and pulse generator locations to ensure they are not contacted during the needle EMG evaluation. This device is likely to cause electrical artifact in nearby muscles; therefore, the SCS should be turned off prior to electrodiagnostic testing [2].

Although there are no specific guidelines pertaining to the safety of nerve conduction studies (NCS) and SCS, the safety can be inferred based on literature demonstrating the safety of NCS with implanted cardiac devices [3]. However, it is recommended to delay NCS until after the temporary SCS trial, since SCS trial leads bypass the skin resistance and electrical current from NCS could theoretically result in stimulation of the spinal cord.

Authors: Mathew Paluck and Ziba Ranjbaran

Supporting References:

1. Kreis, P.G. and S. Fishman, Spinal cord stimulation: percutaneous implantation techniques. 2009, Oxford; New York: Oxford University Press.
2. American Association of Electrodiagnostic Medicine. Guidelines in electrodiagnostic medicine. Risks in electrodiagnostic medicine. Muscle Nerve Suppl, 1999. 8: p. S53-69.
3. London, Z.N. Safety and pain in electrodiagnostic studies. Muscle Nerve, 2017. 55(2): p. 149-159.