Multimodal therapeutic assessment of peripheral nerve stimulation in neuropathic pain: Five case reports with a 20-year follow-up

Neuropathic pain following peripheral nerve lesion is highly resistant to conventional pain treatments but may respond well to direct electrical peripheral nerve stimulation (PNS). In the 1980s, we treated a series of 11 peripheral neuropathic pain patients with PNS. A first outcome assessment, conducted after a 52-month follow-up, revealed that the majority of the patients were significantly improved. Here, we present the results of a second and more comprehensive follow-up, conducted after more than 20 years of PNS usage. Of the six patients still using PNS, five participated in a multimodality assessment of the long-term efficacy of PNS. Home evaluations showed reduced pain ratings and improved quality-of-life during active periods of stimulation. Quantitative sensory testing confirmed the neuropathic character of the pain complaints. PNS had no significant overall effect on tactile detection, cool, warmth, cold pain and heat pain thresholds. Laser-evoked potentials showed an enlarged N2-P2 complex during active PNS. Positron Emission Tomography revealed that PNS decreased activation in the pain matrix at rest and during thermal stimulation. PNS led to increased blood flow not only in primary somatosensory cortex, but also in anterior cingulate and insular cortices, suggesting that besides activation of the dorsal column lemniscal system, other mechanisms may play a role in its analgesic effects. These data show that PNS can provide truly long-term pain relief in carefully selected patients and they provide some objective quantitative data in support of this. They encourage the planning of future prospective studies in a larger cohort of patients.