Laser evoked potentials in amyotrophic lateral sclerosis

The pathophysiological mechanism of the pain in ALS is still unclear. The aim of the study was to evaluate the laser evoked potentials (LEPs) in ALS patients in relation to their clinical features. Twenty-four ALS patients were selected. Pain features were assessed and their intensity was measured by a 0–10 VAS. LEPs were recorded in all patients and in 23 healthy subjects. The dorsum of both hands was stimulated, at laser stimuli intensity of 7.5 W, with 10 s inter-stimulus interval and 25 ms duration. Four electrodes were placed at Cz, T3, T4 and Fz positions, with the reference electrode at the nasion; T3 and T4 electrodes were referred off-line to Fz, in order to detect the N1 component. Latencies of N2, P2 and N1 waves were significantly higher in ALS than in controls. N1 amplitude was significantly increased in ALS patients compared to controls, with a similar trend for the N2–P2 complex. No correlation was found between LEP abnormalities, pain intensity and clinical features. A degeneration of subcortical structures may subtend a delay in the afferent input to the nociceptive cortex in ALS. On the other hand, an increase of pain processing at the cortical level may derive from a potential sensory compensation to motor cortex dysfunction.