Hyperexcitable C nociceptors in fibromyalgia

TLDR

The study aimed to determine whether peripheral C nociceptor dysfunction contributes to fibromyalgia symptoms. C nociceptors were recorded via microneurography in 30 fibromyalgia patients, 17 small‑fiber neuropathy patients, and 9 controls. Most fibromyalgia patients exhibited abnormal C nociceptors, with 76.6 % of silent units showing abnormalities such as spontaneous activity (31 %) and mechanical sensitization (24.2 %), and activity‑dependent conduction slowing was more frequent than in small‑fiber neuropathy or controls. Published in Ann Neurol 2014;75:196–208.

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 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 of 186 C nociceptors in the fibromyalgia group, 114 from small‐fiber neuropathy patients, and 66 from controls. The mechanosensitive 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 0.25Hz 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. ANN NEUROL 2014;75:196–208