Changes in somatic sensitivity during transcutaneous electrical analgesia.

Patients with chronic pain in one limb, who experienced pain reduction with transcutaneous neurostimulation, were examined for sensory perception in that limb before and during electrical analgesia. Contralateral limbs and normal subjects served as controls. Sensory stimuli were quantified, a range of stimuli were presented and data were analyzed according to sensory decision theory. Results showed that, compared to controls, painful limbs show considerable impairment in sensory sensitivity. With transcutaneous neurostimulation, however, sensitivity is improved towards normal, whereas electrical stimulation slightly impairs perception in normal limbs. These results suggest that electrical analgesia involves both peripheral small-fiber blockade and large-fiber stimulation; the latter is more noticeable in the normal limb, but the former effect is predominant when pain reduction occurs in a painful limb.