Laser-evoked potentials habituation in fibromyalgia.

UNLABELLED: Abnormalities of central pain processing play an important role in the pathophysiology of fibromyalgia (FM). The aims of the present study were to: 1) evaluate habituation of laser-evoked potentials (LEP) to repeated painful stimulation of 1 tender and 2 nontender points; and 2) determine correlations between LEP abnormalities and major clinical features of FM. Fourteen consecutive FM outpatients and 13 normal controls were included. LEP were recorded from scalp designations Fz, Cz, Pz, T3, and T4. The dorsum of the right hand, the right supra-orbital zone, and the right knee (a tender point in all patients) were subjected to repeated CO2 laser stimuli. For each stimulation site, recordings were obtained for 3 consecutive series of 20 stimuli. The 3 main findings in FM patients were: 1) an increased amplitude of vertex LEP and subjective laser pain; 2) decreased habituation of vertex LEP and subjective laser pain; and 3) a correlation between reduced N2 wave habituation and the severity of self-reported depressive symptoms. As with other chronic pain syndromes, the pathophysiology of FM may involve a generalized increase in the perception of painful stimuli and reduced habituation of the sensory cortex. PERSPECTIVE: Reduced habituation of cortical responses to laser stimuli in FM patients suggests alterations in the pattern of cortical excitability. This is facilitated by depressive symptoms and abnormalities in central neurotransmission. These findings provide further support for the use of medications with effects on the central nervous system in the management of FM.

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 10s 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.

Effects of affective pictures on pain sensitivity and cortical responses induced by laser stimuli in healthy subjects and migraine patients.

Visually induced analgesia has been correlated with the affective content of pleasant, neutral or unpleasant pictures. The aim of the present study was to assess the effect of affective images vision on laser evoked potentials and pain perception, in a cohort of healthy subjects and migraine patients. Twenty-two healthy subjects and 24 migraine without aura patients (recorded during the inter-critical phase) participated in the study. Eighty-four colour slides, arranged in two blocks, each consisting of 14 pleasant, 14 unpleasant and 14 neutral images, in random presentation, were chosen from the International Affective Picture System. The CO(2) laser stimuli were delivered on the dorsum of the right hand and supra-orbital zone at 7.5-watt intensity and 25-ms duration, in basal condition and during the viewing of affective pictures. Migraine patients expressed higher scores of valence and arousal for pleasant and unpleasant pictures, compared to controls. In both groups, a late positive potential in the 400-700 ms time range was clear for pleasant and unpleasant pictures, but its amplitude was significantly reduced in migraine patients. The pain rating and the N2 component were reduced in both groups during the visual task compared to basal condition. In migraineurs and controls the P2 wave was reduced during the vision of pleasant pictures, compared to basal condition. This indicates that stimulation by images with different affective content reduces subjective pain for a cognitive mechanism of attentive engagement, while a special inhibition of later LEPs is produced by a positive emotional impact. In migraine, affective images are able to modulate pain perception and LEPs, differently from other modalities of distraction, suggesting a possible emotive elaboration of painful stimuli.

Laser evoked potentials in carpal tunnel syndrome.

OBJECTIVES: The aim of this study was to evaluate the function of Adelta fibers at the hand level in patients with clinical symptoms of Carpal Tunnel Syndrome (CTS) using CO(2) laser evoked potentials (LEPs), in light of the intensity and distribution of sensory symptoms and pain. METHODS: Thirty-four CTS outpatients (62 hands) were compared to 23 sex- and age-matched control subjects (46 hands). The periungueal skin of the first, second, third and fifth fingers, and the dorsum of the hands were stimulated in random order. The latency and amplitude of the N2, P2 and N1 components were evaluated with respect to the Nerve Conduction Study (NCS) data, clinical scales, pain intensity and glove-like symptoms distribution. RESULTS: The amplitude of the N2-P2 complex was significantly reduced in CTS hands compared to normal hands after stimulation of the second and third fingers, even in patients with mild nerve conduction impairment. No significant fifth finger LEP abnormalities were found in patients with glove-like distribution symptoms. The N2-P2 amplitude at the second and third fingers was positively correlated with the severity of sensory symptoms. CONCLUSIONS: The involvement of median nerve Adelta fibers in CTS seems to be an early phenomenon, which concurs with the impairment of large motor and sensory afferents and is linked to the severity of the disease. SIGNIFICANCE: The finding of reduced sensory symptoms in patients with severe thin afferents damage, may suggest a slight expression of central sensitisation phenomena in the advanced stage of CTS syndrome.