Quantitative motor unit action potentials (QMUAP) in whiplash patients with neck and upper-limb pain.

INTRODUCTION

Needle EMG studies in patients with whiplash symptoms to document presence of neural injury, such as cervical radiculopathy, are not available.

OBJECTIVE

To document presence of motor unit action potential (MUAP) parameter changes compatible with neurogenic involvement in symptomatic-limb muscles in whiplash induced acute and chronic pain states.

DESIGN

Retrospective review.

SETTING

Out patient quantitative electromyography (QEMG) laboratory.

PARTICIPANTS

72 consecutive patients (mean age 43.6 years) who underwent QEMG between 1/2001 - 12/2004 for electrodiagnosis of neck and upper-limb pain related to auto-accidents (mean symptom duration 15.3 months).

INTERVENTIONS: QEMG with MUAP parameter analysis.

MAIN OUTCOME MEASURES: Amplitude, duration, size-index (SI), percentage of polyphasic units and firing rate analysis in chosen bilateral muscles representing C3-C8 myotomes.

RESULTS

No spontaneous activity noted in muscles examined. Without subsetting symptom duration, symptomatic-side: asymptomatic-side MUAP parameter comparison showed significant increase in MUAP frequency on the symptomatic-side C6-muscle (10.4 +/- 1.3 vs. 9.7 +/- 1.4, p = < 0.05), and C7 muscle (10.0 +/- 1.2 vs. 9.1 +/- 1.1, p < or = 0.01). The symptomatic-side C6-muscle also showed increased percentage of polyphasic-MUAPs (23.7 +/- 13.1 vs. 15.9 +/- 12.7, p < 0.001). Patients with acute symptom duration (< 6 months, mean duration 3.4 +/- 1.4 months, N=26), showed increased percentage of polyphasic MUAPs in the symptomatic-side C6-muscle (27.0 +/- 12.3% vs. asymptomatic 22.2 +/- 17.6%, p < or = 0.05). In patients with chronic symptom duration (> or =6 months, mean duration 22.0 +/- 17.9 months, N=46), symptomatic-side C6-muscle showed increased polyphasic MUAPs (22.2 +/- 13.2%) vs. asymptomatic (15.5 +/- 11.6%), p < or = 0.02, and higher firing rates (10.3 +/- 1.7 vs. 9.6 +/- 1.3 respectively, p < or = 0.003).

CONCLUSIONS

QEMG changes suggest neural injury in symptomatic side C6 and C7 innervated muscles, even in the absence of spontaneous activity. In acute and chronic pain patients a higher percentage of polyphasic MUAPs is noted in the symptomatic side C6 muscle. In chronic pain patients higher MUAP frequencies are noted in the symptomatic side C6 muscle.