79. Laser-evoked potentials in non-organic origin pain

Abstract

Laser-evoked potentials (LEPs) represent the most reliable method to diagnose and follow over time painful small fiber neuropathies. Here, we investigated LEPs in patients with pain of non-organic origin. LEPs were recorded with a Nd:Yag Laser in 4 subjects with pain of non-organic origin, stimulating the dorsum of the hand and the dorsum of the foot bilaterally. We measured the perceptive threshold, latency and amplitude of N1 wave and N2/P2 complex within the painful territory and at contralateral site. We then compared these responses with those obtained in five sex- and age-matched healthy volunterees. We observed a significant increase in amplitude of N1 (p = 0.023) and N2/P2 (p = 0.015) responses in the painful territory compared both with contralateral side and healthy subjects. In patients, an additional positive wave at about 300 ms was detected only when the painfulside was stimulated; this response became more pronounced during stimulus expectation. Our data suggest that increased laser responses characterize subjects with pain of non-organic origin and likely reflect a strong emotional component in the nociceptive experience; the P3 component is probably related to cognitive modulation and anticipation phenomena, thus suggesting a functional (psychogenic) origin of the pain.