Featured Case: June 2026

Contributed by: Poornima Amit Shah, MD, IONM

Case Title

"Interaoperative SSEP Loss: Not Your Usual Story"

Case Description

62 year old male without any significant previous medical history presented with low back pain, numbness along lateral side of legs, calves and soles and a claudication distance of 5 minutes. On examination, there was no motor deficit. Ankle jerks were depressed. Imaging showed lumbar canal stenosis at L3-4 and L4-5 and instability at L3-4. He was planned for minimally invasive spine surgery (MISS) transforaminal lumbar interbody fusion (TLIF) L3-4, MISS decompression L3-4 and L4-5 under mainly intravenous anesthesia and nitrous oxide MAC less than 0.3. Intraoperative neuromonitoring was performed using transcranial motor evoked potentials (TcMEPs), somatosensory evoked potentials (SSEPs) and electromyography (EMG). During exposure, blood pressure rose to 160/110 mm Hg for several minutes and subsequently the right median and right tibial SSEPs were suddenly lost (figure 1). Systematic trouble shooting confirmed all impedances less than 5 Kohms and adequacy of stimulation was observed in the free running EMG. No other EMG change was noted. TcMEPs were well preserved.

Surgeon was informed about the incident. Decision was taken to finish the surgery as planned as quickly as possible. No new changes were noted in the IONM.  Postoperative exam revealed that the patient had mild right sided paresthesias and mild right upper limb weakness. Examination revealed right pronator droop with a mute right plantar and slurred speech.

Figure 1 Image:

Figure 1 Label: Illustration of absent right median and right tibial SSEP- red trace-baseline, black trace- current average, green trace- previous average. EMG- top to bottom- iliopsoas, adductor longus, vastus medialis, tibialis anterior, gastrocnemius, abductor hallucis, abductor pollicis brevis. Sweep speed- 100 ms/div, sensitivity 500 uv/div All electrode impedances- less than 5 kOhms, spectral edge frequency (SEF)-20

Follow-up questions

Question 1: In this type of surgery, surgical manipulation can give rise to following alerts:

1. Changes in lower limb SSEP and MEP
2. Changes in upper limb SSEP and MEP
3. All of above
4. None of the above

Question 2: In this case, SSEP changes can be due to:

1. High impedance of recording electrodes
2. Central pathology
3. Cortical depression due to anesthesia
4. Inadequate stimulation of peripheral nerve

References

1. Amit Jain, A. Jay Khanna, Hamid Hassanzadeh. (2015). Management of intraoperative neuromonitoring signal loss. Seminars in Spine Surgery.Volume 27, Issue 4, 229-232
2. Sunderlin, R. J. (2021). IONM Troubleshooting in Spinal Procedures. The Neurodiagnostic Journal, 61(1), 11–26.
3. Yan X, Pang Y, Yan L, Ma Z, Jiang M, Wang W, Chen J, Han Y, Guo X, Hu H (2022). Perioperative stroke in patients undergoing spinal surgery: a retrospective cohort study. BMC Musculoskelet Disord. 23: 652.