Fibromyalgia syndrome-A laser-evoked potentials study unsupportive of small nerve fibre involvement

Fibromyalgia syndrome (FMS) is a chronic pain syndrome characterized by widespread pain and a variety of non-pain symptoms. Central sensitivity phenomena are found consistently in FMS. Additionally, several researchers proclaimed that a subgroup of FMS patients may present with unrecognized peripheral small fibre neuropathy (SFN). Laser-evoked brain potentials (LEP) are considered as a reliable method for the functional assessment of the thermo-nociceptive system, including the evaluation of SFN.

The aim of this retrospective study was to estimate the prevalence of thermo-nociceptive system dysfunction based on LEPs in FMS.

LEP recordings of 92 FMS patients and 39 age and gender-matched healthy controls were selected from a database collected between 2003 and 2012 with standardized settings for laser stimulation and EEG recording. The N1, N2 and P2 LEP components were identified and characterized by peak latency and amplitude.

None of the FMS patients showed signs of loss of function of the nociceptive responses evoked by A δ-nociceptor activation, compared to healthy controls. 6.5% of the FMS patients had N2-P2 peak-to-peak amplitudes above the upper limit of the 99%-confidence interval. N2-P2 peak-to-peak amplitudes were negatively correlated with age, without age-related differences between groups.

The characteristic signs of a damaged thermo-nociceptive system as revealed by LEPs were absent in this large cohort of FMS patients.

The present research does not support the hypothesis that small fibre neuropathy is a significant contributor to the pathophysiology of FMS.