Hyperexcitable C Nociceptors in Fibromyalgia

Editor’s comment:  Nociceptors are nerve cells that respond to potentially damaging stimuli by sending  signals – usually perceived as pain – to the brain and spinal cord.  In this study, researchers found that the function of certain nociceptors is abnormal in most people with fibromyalgia. 

Abstract:

Objective: To test the hypothesis that peripheral C nociceptor function may be abnormal in fibromyalgia and that C nociceptor dysfunction may contribute to the symptoms reported by these patients.

Methods: Microneurography was used to record from C nociceptors of 30 female patients meeting criteria for fibromyalgia and compared with recordings from 17 female patients with small fiber neuropathy and 9 female controls.

Results: We obtained stable recordings from 186 C nociceptors in the fibromyalgia group, 114 from small fiber neuropathy patients, and 66 from controls.

  • The mechano-sensitive nociceptors in the fibromyalgia patients behaved normally, but the silent nociceptors in 76.6% of fibromyalgia patients exhibited abnormalities.

  • Spontaneous activity was detected in 31% of silent nociceptors in fibromyalgia, 34% in small fiber neuropathy, and 2.2% in controls.

  • Sensitization to mechanical stimulation was found in 24.2% of silent nociceptors in fibromyalgia, 22.7% in small fiber neuropathy, and 3.7% in controls.

  • Abnormally high slowing of conduction velocity when first stimulated at 0.25 Hz was more common in fibromyalgia.

Interpretation: We show for the first time that the majority of fibromyalgia patients have abnormal C nociceptors. Many silent nociceptors exhibit hyperexcitability resembling that in small fiber neuropathy, but high activity-dependent slowing of conduction velocity is more common in fibromyalgia patients, and may constitute a distinguishing feature. We infer that abnormal peripheral C nociceptor ongoing activity and increased mechanical sensitivity could contribute to the pain and tenderness suffered by patients with fibromyalgia.

Source:
Annals of Neurology, November 16, 2013. By Jordi Serra MD, Antonio Collado MD, Romà Solà MD, Francesca Antonelli MD, Xavier Torres MD, Monika Salgueiro MD, Cristina Quiles MD and Hugh Bostock PhD, FRS. Department of Neurology, MC Mutual, Barcelona, Spain; Neuroscience Technologies, Parc Científic de Barcelona, Barcelona.

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