Selective abnormality of the N13 spinal SEP to dermatomal stimulation in patients with cervical monoradiculopathy

The N13 spinal component of somatosensory evoked potentials is modulated by heterotopic noxious conditioning stimulation suggesting an involvement of spinal wide dynamic range neurons

OBJECTIVES

Although somatosensory evoked potentials (SEPs) after median nerve stimulation are widely used in clinical practice, the dorsal horn generator of the N13 SEP spinal component is not clearly understood. To verify whether wide dynamic range neurons in the dorsal horn of the spinal cord are involved in the generation of the N13 SEP, we tested the effect of heterotopic noxious conditioning stimulation, which modulates wide dynamic range neurons, on N13 SEP in healthy humans.

METHODS

In 12 healthy subjects, we performed the cold pressor test on the left foot as a heterotopic noxious conditioning stimulus to modulate wide dynamic range neurons. To verify the effectiveness of heterotopic noxious conditioning stimulation, we tested the pressure pain threshold at the thenar muscles of the right hand and recorded SEPs after right median nerve stimulation before, during and after the cold pressor test.

RESULTS

The cold pressor test increased pressure pain threshold by 15% (p = 0.04). During the cold pressor test, the amplitude of the N13 component was significantly lower than that recorded at baseline (by 25%, p = 0.04).

DISCUSSION

In this neurophysiological study in healthy humans, we showed that a heterotopic noxious conditioning stimulus significantly reduced N13 SEP amplitude. This finding suggests that the N13 SEP might be generated by the segmental postsynaptic response of dorsal horn wide dynamic range neurons.

Unilateral suppression of P/N13' potential amplitude in young patients with persistent numbness due to cervical monoradiculopathy. A case-control study

Objective

The utility of Dermatomal Somatosensory Evoked Potentials (DSEPs) in the diagnostic workup of suspected cervical monoradiculopathy has been limited by significant overlap between measurements obtained from affected versus unaffected roots. In a case-control study, we explored whether, under certain conditions, asymmetry in DSEP parameters may offer significant help in the diagnosis of monoradiculopathy.

Methods

DSEPs were obtained bilaterally from patients with persistent (age range 33-55, n = 10) or intermittent (age range 31-55, n = 7) unilateral sensory symptoms of less than one month duration due to MRI-confirmed cervical monoradiculopathy. DSEPs were also obtained bilaterally from aged-matched asymptomatic volunteers (age range 31-54, n = 8) and older asymptomatic volunteers (age range 57-77, n = 8). Amplitude and latency of the P/N13' potential (negative peak at 13 ms) were measured.

Results

In all ten patients with persistent symptoms, the P/N13' amplitude ratio, defined as P/N13' amplitude on the symptomatic side divided by P/N13' amplitude on the contralateral asymptomatic side, ranged between 0.0 and 0.50 (unilateral suppression). In all seven patients with intermittent symptoms, P/N13' amplitude ratios ranged between 0.60 and 1.00. In all age-matched asymptomatic controls, P/N13' amplitude ratio (side with lower divided by side with higher amplitude) was always at least 0.80. Among older asymptomatic subjects, DSEPs had inconsistent characteristics.

Conclusions

Cervical monoradiculopathy with persistent numbness in young patients (aged up to 55 years) is very strongly associated with unilateral suppression of P/N13' DSEP amplitude. No significant asymmetry is observed in cases of monoradiculopathy with intermittent numbness.

Significance

In young patients with unilateral upper extremity persistent sensory complaints, DSEP amplitude asymmetry, as quantified by the P/N13' ratio, may offer significant help in the diagnosis of monoradiculopathy.

Digital nerve somatosensory evoked potentials and MRI. Correlation analysis in patients with symptomatic cervical spine disorders

OBJECTIVES

Analysis of the relationship between the symptoms, digital nerve somatosensory evoked potentials (D-SEP) and MRI, in patients with symptomatic cervical spine disorders (CSD).

MATERIALS AND METHODS

MRI and D-SEP following electrical stimulation of digits I, III and V in 44 patients.

RESULTS

Symptoms in the fingers correlated significantly with disk herniation at the corresponding cervical level and with spinal cord impingement at one or two adjacent rostral segments on MRI. D-SEP was abnormal in 52% of all patients. Among them, the groups with multiple and single level involved on MRI had 62% and 30% of abnormal somatosensory evoked potentials (SEP), respectively. Digit I-SEP abnormality was more often localized at the root level, while digit V-SEP at the spinal cord level above the dorsal nucleus. D-SEP correlated best with compression of the spinal cord at adjacent upper and especially the most rostral (C3-5) levels on MRI.

CONCLUSIONS

Accurate correlation of D-SEP and symptoms with MRI is essential for correct localization of lesions in patients with CSD.