Coexisting peripheral nerve and cervical cord compression.

Abstract

STUDY DESIGN: The authors investigated the clinical usefulness of recording motor evoked potentials after transcranial magnetic stimulation in coexisting peripheral nerve and cervical cord lesions. OBJECTIVE: To show that the measurement of central motor conduction time from the abductor policis brevis and the abductor digiti minimi can be used as a good screening method for double lesions involving peripheral nerves and the cervical cord. SUMMARY OF BACKGROUND DATA: Transcranial magnetic stimulation has been used in the diagnosis of compressive cervical myelopathy. This technique could be useful in the assessment of patients with an entrapment neuropathy and cervical myelopathy. METHODS: Motor evoked potentials after transcranial magnetic stimulation, compound muscle action potentials, and F waves after supramaximal peripheral nerve stimulation were recorded from the abductor policis brevis and the abductor digiti minimi. The central motor conduction time was calculated by subtracting the peripheral conduction time from the motor evoked potentials latency. RESULTS: Ten patients with coexisting peripheral nerve and cervical cord lesions were evaluated. Two patients did not show satisfactory improvement after the decompression of the entrapment lesions, and six patients had hyperreflexia of lower limbs. In seven of these patients, the central motor conduction time was prolonged an average of 2.5 standard deviation of the normal value. The remaining two patients had spinal cord compression due to the ossification of the posterior longitudinal ligament. The spinal cord compression was demonstrated by magnetic resonance imaging, but the central motor conduction time was normal. Subjective symptoms improved in these two patients after decompressive surgery at the entrapment site alone. CONCLUSIONS: Measurement of the central motor conduction time using motor evoked potentials is an ideal diagnostic approach for patients with coexisting entrapment neuropathy and cervical cord compression.