Laser evoked potentials in fibromyalgia with peripheral small fiber involvement

Objective: To evaluate multichannel laser evoked potentials (LEPs) in patients with fibromyalgia (FM) and small fiber impairment. Methods: We recorded LEPs using 65 electrodes in 22 patients with FM and proximal denervation, 18 with normal skin biopsy, and 7 with proximal and distal intraepidermal nerve fiber density (IENFD) reduction. We considered the amplitude and topographical distribution of N1, N2 and P2 components, and habituation of N2 and P2 waves. The sLORETA dipolar analysis was also applied. We evaluated 15 healthy subjects as controls. Results: We observed reduced amplitude of the P2 component in FM group, without a topographic correspondence with the prevalent site of denervation. Decreased habituation of P2 prevailed in patients with reduced IENFD. The cingulate cortex and prefrontal cortex, were activated in the FM group, without correlation between the degree of denervation and the strength of late wave dipoles. A correlation was noted between anxiety, depression, fibromyalgia invalidity, and pain diffusion. Conclusions: The amplitude and topography of LEPs were not coherent with epidermal nerve fiber density loss. They supposedly reflected the clinical expression of pain and psychopathological factors. Significance: Multichannel LEPs are not the expression of small fiber impairment in FM. Rather, they reflect the complexity of the disease.