Clinical neurophysiology

Recommendations of the International Society of Intraoperative Neurophysiology for intraoperative somatosensory evoked potentials

Somatosensory evoked potentials (SEPs) allow to obtain functional and localising information about the dorsal somatosensory system. SEPs are complementary to motor evoked potentials (MEPs) and represent a substantial contribution to intraoperative neurophysiologic monitoring (IONM).1

This manuscript is not a clinical practice guideline; it rather suggests recommendations of the International Society of Intraoperative Neurophysiology for intraoperative SEPs (also endorsed by the International Federation of Clinical Neurophysiology) based on currently available scientific evidence. After reviewing basis of anatomy and physiology it provides information about methodology and indications of SEPs in IONM.  It emphasises the optimal derivations for SEP monitoring and its differences comparing traditional SEPs derivation. Optimising derivations for IONM has the advantage of increasing Signal-to-noise ratio (SNR) facilitating thus SEPs execution and reproducibility.  The authors criticise the traditional SEP warning criteria of > 50% amplitude reduction or > 10% latency prolongation from baseline suggesting instead adaptive warning criteria: any visually obvious amplitude reduction from recent pre-change values and clearly exceeding variability, especially when abrupt and focal, should arise suspicion of a pathological decrement. In addition, concurrent evaluation of MEPs or looking for further SEP deterioration in subsequent trials is recommended to corroborate borderline cases. In comparison to traditional criteria, this approach could reduce the likelihood of technical false results.2,3

Finally, the authors review the indications of SEPs monitoring, the most common being by far orthopaedic spine surgery. Other important indications are conditions requiring perirolandic brain, posterior fossa and spinal surgery and descending aortic procedures.  

  • SEPs represent a substantial portion of IONM
  • Optimising derivations for IONM has the advantage of increasing Signal-to-noise ratio (SNR) facilitating execution and reproducibility of SEPs
  • Traditional SEP warning criteria can be modified to adaptive warning criteria to improve the likelihood of detecting pathological SEPs decrement.

References:

1. Nuwer MR, Emerson RG, Galloway G, Legatt AD, Lopez J, Minahan R, Yamada T,

Goodin DS, Armon C, Chaudhry V, Gronseth GS, Harden CL; Therapeutics and Technology Assessment Subcommittee of the American Academy of Neurology; American Clinical Neurophysiology Society. Evidence-based guideline update: intraoperative spinal monitoring with somatosensory and transcranial electrical motor evoked potentials: report of the Therapeutics and Technology Assessment Subcommittee of  the American Academy of Neurology and the American Clinical Neurophysiology Society. Neurology. 2012;78:585-589. doi: 10.1212/WNL.0b013e318247fa0e. PubMed PMID: 22351796.

2: MacDonald DB, Al Zayed Z, Al Saddigi A. Four-limb muscle motor evoked potential and optimized somatosensory evoked potential monitoring with decussation assessment: results in 206 thoracolumbar spine surgeries. Eur Spine J. 2007;16 Suppl 2:S171-187. PubMed PMID: 17638028; PubMed Central PMCID: PMC2072898.

3: MacDonald DB, Al Zayed Z, Khoudeir I, Stigsby B. Monitoring scoliosis surgery with combined multiple pulse transcranial electric motor and cortical somatosensory-evoked potentials from the lower and upper extremities. Spine. 2003;28:194-203. PubMed PMID: 12544939.