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.