Small fibre impairment predicts neuropathic pain in Guillain-Barré syndrome.

The mechanisms of neuropathic pain (NP) in Guillain Barré syndrome (GBS) are currently unknown. It has recently been shown that acute neuropathy of GBS not only affects large myelinated fibres but also small nociceptive fibres. In this prospective longitudinal 18 months study, we investigated the role of small fibre impairment in NP in GBS (n=30). Small fibres were assessed by quantifying cold and warm detection and pain thresholds and responses to suprathreshold painful thermal and mechanical stimuli. Nerve conduction velocities and mechanical detection thresholds assessed large myelinated fibres. Detection thresholds particularly at the lower limbs were significantly impaired in patients with GBS compared to 15 healthy controls. GBS patients with NP (n=13) had more severe impairment of cold detection thresholds (p=0.04), heat pain thresholds (p=0.03) and responses to suprathreshold heat stimuli (p=0.017) in the foot compared with those without pain or with non-neuropathic pain (n=17). Large fibre dysfunction and motor disability were similar between groups. Small fibre sensory impairment at the acute stage was correlated with the intensity of burning pain (Rho: -0.72; p=0.01 for cold detection; Rho: 0.72; p=0.02 for heat pain) and predicted residual NP (odds 4.1 p=0.04 for heat pain). These findings emphasize the importance of nociceptive fibre impairment in NP in GBS at both acute and chronic stages and suggest similarities between the mechanisms of NP in GBS and those of small fibre painful sensory polyneuropathies.