Abstract
The nociceptive withdrawal reflex (NWR) is used to probe spinal cord excitability in chronic pain states. Here, we used an automated and unbiased procedure for determining the NWR threshold and compared the reflex thresholds and corresponding pain ratings in a well-characterized cohort of fibromyalgia (n = 29) and matched healthy controls (n = 21). Surface electrical stimuli were delivered to the foot in a stepwise incremental and decremental manner. The surface electromyographic activity was recorded from the ipsilateral tibialis anterior muscle. Fibromyalgia patients reported significantly higher scores for psychological distress and pain-related disability and a significantly lower score for perceived state of health compared to the matched controls. The subjective pain ratings were significantly higher in patients. The NWR thresholds were similar to the controls. In the patients, but not in controls, the NWR thresholds and subjective pain ratings were significantly correlated. Our results showed an increased subjective pain sensitivity in fibromyalgia, but we found no evidence for spinal sensitization based on the reflex measures.
Highlights
The nociceptive withdrawal reflex (NWR) is a polysynaptic spinal reflex evoked by painful cutaneous stimuli
We compared the thresholds for eliciting the NWR in fibromyalgia patients and matched healthy controls
We found no statistical difference in the NWR thresholds between the two groups
Summary
The nociceptive withdrawal reflex (NWR) is a polysynaptic spinal reflex evoked by painful cutaneous stimuli. Studies show that the cutaneous noxious electrical stimulation of the distal lower leg elicits a reflex of muscle contraction and inhibition, resulting in the withdrawal of the limb from the stimulus [1,2,3]. The NWR is a protective reflex elicited by potentially harmful stimuli and involves both sensory and motor systems. An alternative approach is to stimulate the sole of the foot and record the response of the ipsilateral tibialis anterior muscle [13,14,15,16] Both methods evoke a withdrawal reaction with the flexion of the knee and ankle joints, but the foot arch-to-tibialis anterior approach is more effective in eliciting the reflex [14]
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