Transcranial Motor-Evoked Potentials Provide More Reliable Intraoperative Neuromonitoring Than Somatosensory-Evoked Potentials in Charcot-Marie-Tooth Patients Undergoing Periacetabular Osteotomy for Hip Dysplasia

Abstract

Background

Charcot-Marie-Tooth (CMT) disease is a common inherited progressive sensorimotor neuropathy which can complicate intraoperative monitoring (IOM). Transcranial motor-evoked potentials (TcMEPs) have been found to be effective in obtaining IOM in CMT patients undergoing spine surgery. The aim of this study was to examine the effectiveness of TcMEPs and somatosensory-evoked potentials (SSEPs) in IOM in CMT patients undergoing periacetabular osteotomies (PAOs) for hip dysplasia.

Methods

A retrospective case series was conducted in all CMT patients aged <19 years at a single institution who underwent PAO for hip dysplasia from 2020 to 2025. Demographics, diagnosis, IOM data, and perioperative results were recorded.

Results

In total, 102 CMT patients from our institution’s specialty clinic were reviewed. Fifteen (15%) had hip dysplasia. Of these, 7 had PAO surgery, with 6 having PAO with IOM. Five of 6 of study patients had the CMT1A subtype. All patients had absent or greatly reduced SSEPs. Five of the 6 (83%) had obtainable TcMEPs that could be used for IOM but required increased sweep lengths and/or signal intensities. No notable complications related to IOM were noted.

Conclusions

TcMEPs are preferred to SSEPs when monitoring interoperatively during PAO in CMT patients with hip dysplasia. Increased sweep lengths and/or signal intensities were required. Preoperative CMT diagnosis allows anticipation of IOM difficulties by the technician to make appropriate changes to allow monitoring.

Key Concepts

• (1)Charcot-Marie-Tooth (CMT) is a common inherited progressive sensorimotor neuropathy which can complicate intraoperative monitoring (IOM).
• (2)Fifteen percent of CMT patients have hip dysplasia that may require surgical intervention. Surgeons should be aware of potential technical issues with IOM if this is requested for the procedure.
• (3)Somatosensory-evoked potentials (SSEPs) are greatly reduced or absent in CMT patients undergoing periacetabular osteotomy (PAO) for hip dysplasia. Use of transcranial motor-evoked potentials (TcMEPs) improves the ability to obtain baseline IOM with increased sweep lengths and increased signal intensities
• (4)TcMEPs are preferred to SSEPs when obtaining IOM during PAO surgery in CMT patients with hip dysplasia.

Level of Evidence

IV, Retrospective case series

Introduction

Charcot-Marie-Tooth (CMT) disease is a progressive, inherited sensory and motor neuropathy with over 130 genetic variants documented and a prevalence of 1 in 2,500 to 1 in 10,000 pediatric patients [[1], [2], [3], [4]]. The condition predisposes to significant orthopaedic manifestations, including pes cavus, scoliosis, and hip dysplasia, often necessitating surgical intervention [[5], [6], [7], [8]]. Intraoperative monitoring (IOM) is used to do real-time assessments of nerve integrity in order to minimize nerve injury that can occur during a surgical procedure, but its interpretation in CMT patients can be complicated by baseline electrophysiologic abnormalities such as slowed conduction and reduced response amplitude [9,10]. In scoliosis surgery, transcranial motor-evoked potentials (TcMEPs) improved the ability to obtain baseline IOM with CMT patients when compared to somatosensory-evoked potentials (SSEPs) [11]. CMT patients with hip dysplasia have been shown to benefit from acetabular reorientation surgeries (primarily periacetabular osteotomy [PAO] and also triple pelvic osteotomy) [12]. The rate of major nerve injury during PAO is approximately 2%. IOM has been recommended, with IOM actionable alerts found in 11% (1/9) of PAO cases in a recent paper by Keil et al. [13] However, the effectiveness of IOM to monitor for nerve injury in CMT PAO cases has not previously been reported.

This retrospective study examines pediatric hip dysplasia patients with CMT disease who underwent PAO with intraoperative neuromonitoring (IOM), highlighting the technical challenges and considerations required for this population.

We hypothesized that IOM could be accomplished during PAO surgery by using TcMEPs with increased sweep times and stimulus intensities.

Materials and methods

This institutional review board–approved retrospective study assessed pediatric patients with CMT who underwent PAO with IOM at our institution 2020–2025. IOM is used in all PAO cases in our institution. Patient demographics, diagnosis confirmation (clinical and genetic), and perioperative details were recorded. Standard neuromonitoring modalities utilized included somatosensory evoked potentials (SSEPs) and TcMEPs, with adjustments to sweep times and stimulus intensities documented. All patients underwent general endotracheal anesthesia, with remifentanil, ketamine, phenylephrine, and propofol. Succinylcholine was not used due to the theoretical risk of hyperkalemia. None of the patients received paralytics, which would reduce motor action potentials in IOM.

Results

Our multidisciplinary clinic currently follows 102 pediatric patients aged 2–19 years with CMT disease. Every patient in the multidisciplinary clinic is radiographically screened for scoliosis and hip dysplasia at presentation and at 2- to 4-year intervals. Fifteen of these patients have or have had hip dysplasia. Seven patients have undergone a PAO, of which 6 had IOM in the study period from 2020 to 2025, aged 9–14 years (mean age: 11.3 years) (Table 1). Of those, 5 of 6 have the CMT1A subtype. Five of 6 patients (83%) had unobtainable SSEPs. One patient had obtainable SSEP responses, but latencies were significantly delayed. Five of 6 (83%) had obtainable TcMEPs. In case 1, the inability to acquire baseline IOM signals with SSEPs or TcMEPs resulted in surgical cancellation which prompted an evaluation to establish a CMT diagnosis. IOM was not utilized when the surgery was subsequently performed. Cases 2–6 demonstrated absent or significantly delayed SSEP responses (Fig. 1), whereas TcMEP monitoring—particularly with increased sweep length and stimulus intensities—provided more consistent intraoperative feedback (Fig. 2). For example, in case 6, posterior tibial nerve SSEPs were not obtainable despite increased sweep time to 25 ms/div and increased stimulation to 65 mA, while TcMEPs were recorded successfully from all extremities with an increased sweep time of 15 ms/division. These cases required iterative technical adjustments, emphasizing the need for individualized monitoring strategies in CMT patients.

Table 1.

Pediatric CMT patients undergoing PAO with IOM.

Case	Age at surgery (years)	Diagnosis	IOM findings	Adjustments by IOM technologist, communication with surgeon	Outcome
1	14	CMT 1A: Diagnosed postoperatively, genetic confirmation initiated after IOM findings	SSEP and TcMEP unobtainable	SSEPs: increased stimulus intensity to 65 mA. TcMEPs: increased stimulus intensity, warmed patient, and increased mean arterial pressure. The second technologist verified connections and stimulus delivery. An IOM medical director and 2 neurologists were consulted.	Surgery canceled. PAO performed after diagnosis confirmed, completed without IOM
2	10	CMT 1A: diagnosed preoperatively by family history	SSEP responses delayed; TcMEP responses obtainable after increased sweep length and stimulus intensity	Surgeon aware that SSEPs responses were delayed. SSEP sweep length changes to 40 ms/div from 15 ms/div. TcMEPs stimulus intensity increased to 500 V and sweep length increased to 25 ms/div	PAO completed, no complications
3	10	CMT 1A: diagnosed preoperatively by genetic testing	SSEP unobtainable, TcMEP responses after increased sweep and stimulus intensity	Surgeon aware of unobtainable SSEPs. TcMEPs stimulus intensity increased from 200 V to 600 V. Sweep length increased to from 10 ms/division to 50 ms/division	PAO completed, no complications
4	12	CMT 1A: diagnosed preoperatively by genetic testing	SSEP unobtainable, TcMEP responses (low amplitude) after increased sweep and stimulus intensity	Unobtainable SSEPs despite increased stimulus intensity of 45 mA and sweep length to 50 ms/division. TcMEP stimulus intensity was increased to 600 V and sweep length increased to 25 ms/division. Despite these technical adjustments, there was still MEP variability which communicated to surgeon. No change in operative plan.	PAO completed, no complications
5	9	CMT1A: diagnosed preoperatively by genetic testing	SSEP unobtainable, TcMEP low amplitude MEPs despite increased sensitivity and stimulus intensity	Surgeon aware that there were no SSEPs available for monitoring. TcMEPs stimulus intensity increased from 200 V to 600 V and sweep length increased to 15 ms/division. MEPs were labile through surgery.	PAO completed, no complications
6	13	CMT X: diagnosed preoperatively	SSEPs unobtainable, TcMEP responses obtainable after increased sweep length	Surgeon aware that there were no SSEPs available for monitoring. TcMEPs stimulus intensity increased to 450 V and sweep length increased to 15 ms/division.	PAO completed, no complications

CMT, Charcot-Marie-Tooth; IOM, intraoperative monitoring; MEP, motor evoked potentials; PAO, periacetabular osteotomy; SSEP, somatosensory-evoked potential; TcMEP, transcranial motor-evoked potential.

Figure 1.

SSEP monitoring during PAO surgery in patient with normal SSEPs (A) and patient with CMT with unobtainable SSEPs (B). CMT, Charcot-Marie-Tooth; PAO, periacetabular osteotomy; SSEP, somatosensory-evoked potential.

Figure 2.

TcMEPs monitoring during PAO surgery in patient with normal TcMEPs (A) and patient with CMT with unobtainable TcMEPs (B). CMT, Charcot-Marie-Tooth; PAO, periacetabular osteotomy; TcMEP, transcranial motor-evoked potential.

Discussion

The technical hurdles for IOM in pediatric patients with CMT are considerable, primarily due to slowed nerve conduction and low-amplitude responses characteristic of the disease. SSEP responses are of low amplitude in normal patients, and in patients with CMT, significantly reduced or absent amplitudes and prolonged latencies make SSEPs difficult to obtain. In two studies of IOM in patients with CMT undergoing scoliosis surgery, only 20–25% of patients had obtainable SSEPs, similar to the 17% rate found in this study [6,11]. In contrast, TcMEPs for IOM can improve the ability to obtain responses but require increasing the stimulus intensity and/or increasing the sweep speed. Increasing the stimulus intensity improves the ability to obtain responses in inexcitable nerves. Changing the sweep speed allows detection of slowed responses. Since there were no “alerts” or adverse neurological outcomes in the study’s patients, the actual sensitivity and specificity of using TMcEPs for PAOs in CMT is not measurable. However, the spine surgery literature shows that TcMEP monitoring is a highly sensitive and specific test for detecting new spinal cord injuries sensitivity (mean: 91% [95% confidence interval {CI}: 34%–100%]) and specificity (mean: 96% [95% CI: 92–98%]) [14].

Most of this study’s patients have CMT1A, the most common subtype, which causes demyelination. This study shows that TcMEPs are preferred over SSEPs for surgical IOM in the CMT1A population undergoing PAO surgery. We would expect that the CMT2 subtype, which is characterized by axonal degeneration, would have even more difficulties with IOM.

CMT is a very common neuromuscular disorder, and 15% of the CMT patients in our specialty clinic have associated hip dysplasia. To avoid IOM difficulties in the operating room caused by unrecognized CMT, hip surgeons should perform a thorough preoperative orthopaedic history and examination when evaluating a patient with hip dysplasia: asking about pertinent family history including CMT or neuropathy, pulmonary deficiencies, and hand weakness, observing gait, examining feet and spine, and completing a neurologic exam including reflexes, strength, sensation, and proprioception. Expert multidisciplinary evaluation is helpful and should include workup for genetic etiologies using available neuropathy panels. Accurate preoperative characterization of the neuropathy—including genetic confirmation—is recommended to anticipate monitoring limitations and optimize surgical planning. Recognition of adjustments need during IOM by technologists familiar with this diagnosis is crucial to successful monitoring.

Conclusions

Hip dysplasia was found in 15% of our specialty clinic’s CMT patients. Intraoperative neuromonitoring in children with CMT undergoing PAO for hip dysplasia was complicated by unreliable or absent SSEP signals in all study patients. TcMEP responses were obtainable in the majority of this study’'s patients but necessitated higher technical vigilance and individualized electrophysiologic adjustments, like increased sweep speed and stimulus intensity. TcMEPs are preferred over SSEPs for IOM for this population. Confirmation of CMT before PAO surgery allows proper planning for IOM and avoids unnecessary delay of surgical interventions.

Author contributions

Michele L. Yang: Writing – review & editing, Writing – original draft, Visualization, Project administration, Methodology, Investigation, Formal analysis, Data curation, Conceptualization. Susan Apkon: Writing – review & editing, Resources. Carolyn Kelley: Writing – review & editing, Writing – original draft, Data curation. Meghan Moore Burk: Writing – review & editing, Writing – original draft, Conceptualization. Caitlyn Silver: Writing – review & editing. Kelli Johnson: Writing – review & editing, Writing – original draft. Sayan De: Writing – review & editing, Writing – original draft, Investigation. Ella Harrington: Writing – original draft. Allison Wheeler: Writing – original draft. Anthea Homme: Writing – original draft, Visualization, Investigation, Formal analysis, Data curation. Margaret Siobhan Murphy-Zane: Writing – review & editing, Writing – original draft, Project administration, Methodology, Investigation, Formal analysis, Data curation, Conceptualization.

Ethics approval and consent

The authors declare that no patient consent was necessary as no images or identifying information is included in the article.

Funding

There are none to declare.

Declaration of competing interests

The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: Margaret Siobhan Murphy-Zane has edited articles for JPOSNA in the past and acts as chair for the POSNA Patient Education and Media Relations committee, which includes Orthokids.org, but she has had no involvement in the peer review of this article and had no access to information regarding its peer review. Full responsibility for the editorial process for this article was delegated to another journal editor. If there are other authors, they declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.