Editor's Comment: In this study, researchers measured the blood flow in the palms (glabrous skin) of people with fibromyalgia and controls. They discovered that people with FM had more vasodilation in the tiny little arterioles (smaller than arteries) that connect to the tiny little venules (smaller than veins) that connect to each other through shunts. These shunts allow blood flowing from the heart to flow back to the heart. Simply put, the arterioles in people with FM are remaining too dilated, which the researchers say is causing the nerves to become overly sensitive. The result is pain in the hands of people with FM.
Excessive Peptidergic Sensory Innervation of Cutaneous Arteriole-Venule Shunts (AVS) in the Palmar Glabrous Skin of Fibromyalgia Patients: Implications for Widespread Deep Tissue Pain and Fatigue.
OBJECTIVE: To determine if peripheral neuropathology exists among the innervation of cutaneous arterioles and arteriole-venule shunts (AVS) in fibromyalgia (FM) patients.
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SETTING: Cutaneous arterioles and AVS receive a convergence of vasoconstrictive sympathetic innervation, and vasodilatory small-fiber sensory innervation. Given our previous findings of peripheral pathologies in chronic pain conditions, we hypothesized that this vascular location may be a potential site of pathology and/or serotonergic and norepinephrine reuptake inhibitors (SNRI) drug action.
SUBJECTS: Twenty-four female FM patients and nine female healthy control subjects were enrolled for study, with 14 additional female control subjects included from previous studies. AVS were identified in hypothenar skin biopsies from 18/24 FM patient and 14/23 control subjects.
METHODS: Multimolecular immunocytochemistry to assess different types of cutaneous innervation in 3 mm skin biopsies from glabrous hypothenar and trapezius regions.
RESULTS: AVS had significantly increased innervation among FM patients. The excessive innervation consisted of a greater proportion of vasodilatory sensory fibers, compared with vasoconstrictive sympathetic fibers. In contrast, sensory and sympathetic innervation to arterioles remained normal. Importantly, the sensory fibers express a2C receptors, indicating that the sympathetic innervation exerts an inhibitory modulation of sensory activity.
CONCLUSIONS: The excessive sensory innervation to the glabrous skin AVS is a likely source of severe pain and tenderness in the hands of FM patients. Importantly, glabrous AVS regulate blood flow to the skin in humans for thermoregulation and to other tissues such as skeletal muscle during periods of increased metabolic demand. Therefore, blood flow dysregulation as a result of excessive innervation to AVS would likely contribute to the widespread deep pain and fatigue of FM. SNRI compounds may provide partial therapeutic benefit by enhancing the impact of sympathetically mediated inhibitory modulation of the excess sensory innervation.
Source: Pain Medicine, May 20, 2013. By Phillip J. Albrecht PhD, Quanzhi Hou MD PhD, Charles E. Argoff MD, James R. Storey MD, James P. Wymer MD PhD, and Frank L. Rice PhD. Integrated Tissue Dynamics, LLC, Rensselaer, New York, USA; Center for Neuropharmacology & Neuroscience, Albany Medical College, Albany, New York, USA.