Neurophysiological pain and sensory disorders correlates in patients with syringomyelia
Short-latent and pain-related long-latent somatosensory evoked potentials (SEP) in response to electrical stimulation of n. medianus, n. tibialis and n. mandibularis were studied in 28 patients with syringomyelia. During stimulation in the area of pain-temperature sensitivity disturbance, reduced amplitude of early components N13, N18 and late components P3, N3, P4, N4 (100-500 ms) was detected. In patients with neuropathic pain, increased amplitude of the middle latency waves P2, N2 (40-100 ms) and low amplitude ratio P4/P2 (normal values = 1.5) were found. Patients with stimulus-evoked pain (allodynia and hyperaesthesia) had shortened N18 peak latency, decreased motor threshold and grossly attenuated and delayed P3, N3, P4 (100-350 ms) in SEP after stimulation of the hypersensitive side. In patients without pain, the amplitude of the late tibial SEP was elevated. The results obtained can be used as diagnostic criteria of syringomyelia. The character of SEP changes in patients with neuropathic pain support the hypothesis of central sensitization and abnormal pain transmission through the fast conducting of pain and temperature afferents.