Segmental evaluation of the peripheral nerve using tibial nerve SEPs for the diagnosis of CIDP

Tibial nerve SEPs in diagnosing lumbar spinal stenosis: The utility of segmental evaluation using P15 and N21

Objective

To establish the utility of the additional evaluation of the P15 potential generated at the greater sciatic foramen in the tibial nerve somatosensory evoked potentials (SEPs) in diagnosing lumbar spinal stenosis (LSS).

Methods

We retrospectively reviewed tibial nerve SEP findings in patients having MRI-confirmed LSS at the cauda equina or conus/epiconus region. P15 and N21 potentials were recorded and the following findings were defined as localizing abnormalities: 1) normal P15 latency either with prolonged P15-N21 interval or with absent N21; 2) decreased ratio of the N21 amplitude to P15 amplitude. As non-localizing abnormalities, N21 and P38 latencies were also evaluated. Tibial nerve F-wave findings were also investigated.

Results

According to the entry criteria, 18 patients were included, 15 with cauda equina lesions and 3 with conus/epiconus lesions. Localizing abnormalities in SEPs were found in 67% of patients, achieving significantly higher sensitivity than delayed P38 latency (28%), and higher sensitivity than N21 abnormalities (39%), though this was not significant. Localizing abnormalities were observed even in 6 out of 11 patients lacking both sensory symptoms and signs. Tibial nerve F-wave was abnormal in 36% of 14 patients with F-wave examinations, whereas the localizing abnormalities in SEPs were found in 64% of the same patient population. P15 amplitude was depressed in 4 patients (22%), which may indicate the involvement of the dorsal root ganglion in LSS, although its latency was normal even for these patients.

Conclusions

Tibial nerve SEPs with the recording of P15 and N21 potentials achieved sufficiently high sensitivity in diagnosing LSS. They have the advantage over F-wave in that they can localize the lesion at the cauda equina or conus/epiconus level.

Significance

Tibial nerve SEPs are promising in evaluating LSS, especially in documenting sensory tract involvement in cases lacking sensory symptoms/signs.

Utility of the tibial nerve somatosensory evoked potentials in differentiating between neuromyelitis optica spectrum disorders and multiple sclerosis

BACKGROUND

Somatosensory evoked potentials (SEPs) are widely used for the diagnosis and evaluation of neuromyelitis optica spectrum disorder (NMOSD) and multiple sclerosis (MS). However, whether the parameters of tibial nerve SEPs can help to distinguish NMOSD from MS remains unclear. Thus, the aim of this study was to investigate the utility of tibial nerve SEP parameters in differentiating patients with NMOSD and MS.

METHODS

The clinical data of patients with NMOSD or MS treated in our institution between 2005 and 2021 were retrospectively extracted from our electronic database. Additional inclusion criteria were presentation with sensory symptoms in the lower extremities with corresponding lesions in the magnetic resonance images as well as available data on anti-aquaporin-4 antibodies and tibial nerve SEPs. The Z-scores of the N21-P38 interval (central sensory conduction time), P38 latency, and P38 amplitude were compared between the patients with NMOSD and MS. The relationship of disease severity with the parameters of the tibial nerve SEPs was also evaluated.

RESULTS

Twenty patients with NMOSD and 13 patients with MS were enrolled. The Z-scores of the N21-P38 interval and P38 latency were significantly higher in the MS group than in the NMOSD group (p < 0.05 and p < 0.01, respectively), whereas there was no difference in the Z-scores of the P38 amplitude between the two groups. In the MS group, only the N21-P38 interval and P38 latency were significantly correlated with disease severity (p < 0.05 and p < 0.01, respectively). In contrast, none of the tibial nerve SEP parameters were significantly correlated with disease severity in the NMOSD group.

CONCLUSION

Evaluation of the N21-P38 interval and P38 latency in tibial nerve SEPs potentially helps in differentiating between NMOSD and MS.

Diagnostic challenges in chronic inflammatory demyelinating polyradiculoneuropathy

Chronic inflammatory demyelinating polyradiculoneuropathy (CIDP) consists of a spectrum of autoimmune diseases of the peripheral nerves, causing weakness and sensory symptoms. Diagnosis often is challenging, because of the heterogeneous presentation and both mis- and underdiagnosis are common. Nerve conduction study (NCS) abnormalities suggestive of demyelination are mandatory to fulfil the diagnostic criteria. On the one hand, performance and interpretation of NCS can be difficult and none of these demyelinating findings are specific for CIDP. On the other hand, not all patients will be detected despite the relatively high sensitivity of NCS abnormalities. The electrodiagnostic criteria can be supplemented with additional diagnostic tests such as CSF examination, MRI, nerve biopsy, and somatosensory evoked potentials. However, the evidence for each of these additional diagnostic tests is limited. Studies are often small without the use of a clinically relevant control group. None of the findings are specific for CIDP, meaning that the results of the diagnostic tests should be carefully interpreted. In this update we will discuss the pitfalls in diagnosing CIDP and the value of newly introduced diagnostic tests such as nerve ultrasound and testing for autoantibodies, which are not yet part of the guidelines.

[Role of short-latency somatosensory evoked potential in the diagnosis of chronic inflammatory demyelinating polyneuropathy]

OBJECTIVE

To investigate the role of short-latency somatosensory evoked potential (SSEP) in the diagnosis of chronic inflammatory demyelinating polyneuropathy (CIDP).

METHODS

A total of 48 children with a confirmed or suspected CIDP and 40 healthy children were enrolled. Nerve electrophysiological examination and/or SSEP examination was performed (the children in the healthy control group only underwent SSEP examination). Four-lead electromyography was used for nerve electrophysiological examination, including at least 4 motor nerves and 2 sensory nerves. N6 (elbow potential), N13 (cervical cord potential), and N20 (cortex potential) of the median nerve and N8 (popliteal fossa potential), N22 (lumbar cord potential), and P39 (cortex potential) of the tibial nerve were observed by SSEP examination.

RESULTS

Among the 48 children with CIDP, 35 had demyelination in both motor and sensory nerves, 8 had demyelination in sensory nerves, and 5 had axonal degeneration. SSEP examination showed that 7 had conduction abnormality in the trunk of the brachial plexus and/or the posterior root and 33 had damage in the lumbosacral plexus and/or the posterior root. The 40 children with abnormal findings of SSEP examination included 8 children with affected sensory nerves and 5 children with secondary axonal degeneration who did not meet the electrophysiological diagnostic criteria for CIDP. Compared with the healthy control group, the CIDP group had significantly prolonged latency periods of N13 and N22 (P<0.05).

CONCLUSIONS

SSEP can be used for the auxiliary diagnosis of CIDP, especially in CIDP children with affected sensory nerves or secondary axonal degeneration.

Somatosensory evoked potentials in chronic inflammatory demyelinating polyradiculoneuropathy

PURPOSE

Somatosensory evoked potentials (SEPs) offer complementary results to those of nerve conduction studies and contribute to the electrodiagnostic criteria of chronic inflammatory demyelinating polyradiculoneuropathy.

METHODS

We performed nerve conduction studies and SEPs in patients with symmetrical motor weakness, areflexia, and/or sensory disturbances lasting for at least 8 weeks. We determined two groups according to the electrodiagnostic criteria of the European Federation of Neurological Societies. Group 1 included patients who met the definite or probable electrodiagnostic criteria, and group 2 included patients who met the possible electrodiagnostic criteria. We also compared SEPs results with those of controls (group of healthy subjects).

RESULTS

Sixteen patients (14 men; mean age, 59 ± 17.3 years) were included in the study. The latencies of potentials N9, N13, N7, and N22 and the intervals N9-N13 and N7-N22 were significantly increased in patients compared with controls. The N9/iP14 amplitude ratio was significantly lower in patients. There was no significant difference in the latencies of SEPs between the two groups of patients.

CONCLUSIONS

We confirm the contribution of SEPs as complementary information to nerve conduction studies in chronic inflammatory demyelinating polyradiculoneuropathy diagnosis. In addition to the usual abnormalities, a decrease in the N9/iP14 amplitude ratio could potentially be used as an electrodiagnostic criterion.