Hyperexcitable C nociceptors in fibromyalgia.
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.


CONCLUSIONS
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.
Department of Neurology, MC Mutual, Barcelona, Spain; Neuroscience Technologies, Barcelona Science Park, Barcelona, Spain.
Jordi
J
Serra
Antonio
A
Collado
Romà
R
Solà
Francesca
F
Antonelli
Xavier
X
Torres
Monika
M
Salgueiro
Cristina
C
Quiles
Hugh
H
Bostock
D000328:Adult; D001703:Biophysics; D016022:Case-Control Studies; D015331:Cohort Studies; D004558:Electric Stimulation; D005260:Female; D005356:Fibromyalgia / Q000188:drug therapy / Q000473:pathology* / Q000503:physiopathology*; D006801:Humans; D006930:Hyperalgesia / Q000503:physiopathology; D008875:Middle Aged; D036421:Nerve Fibers, Unmyelinated / Q000502:physiology*; D009431:Neural Conduction / Q000502:physiology; D009619:Nociceptors / Q000145:classification / Q000473:pathology*; D017288:Pain Threshold / Q000502:physiology; D055815:Young Adult