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Fibromyalgia is a syndrome that affects an estimated 2% of the population in the U.S (Bull Hosp Jt Dis 2010; 68:157). Patients report fatigue, sleep disruption, and cognitive symptoms, with tenderness to palpation and an otherwise normal clinical examination. Laboratory evaluation is usually unremarkable. The coexistence of neuropathic features of pain implicating small-fiber axonal loss in the setting of fibromyalgia has raised the hypothesis that pain in fibromyalgia is a neuropathic phenomenon.
In this study, 117 women with fibromyalgia syndrome (FMS) underwent a neurologic examination, questionnaire assessment, neurophysiology assessment, and small-fiber tests such as skin-punch biopsy, corneal confocal microscopy, microneurography, quantitative sensory testing (including C tactile afferents), and pain-related evoked potentials. Women with major depressive disorder and chronic pain and healthy women served as controls.
Intraepidermal nerve fiber density was lower in patients with FMS than in healthy controls. Similarly, corneal innervation was reduced in patients with FMS. Small- and large-fiber sensory dysfunction was seen in FMS. The FMS group also had higher 1B nociceptors conduction velocities. Generalized skin denervation was associated with a more severe FMS phenotype.
Evdokimov D et al. Reduction of skin innervation is associated with a severe fibromyalgia phenotype. Ann Neurol 2019 Oct; 86:504. (https://doi.org/10.1002/ana.25565)
Comment
Although fibromyalgia is a recognized syndrome, the previously observed presence of small-fiber impairment in 30% to 70% of patients with FMS helps to explain pain in these patients. This well-conducted study in a large cohort of FMS patients supports growing evidence of small-fiber impairment in patients with FMS. Better understanding of its pathophysiology will probably lead to better treatments for FMS.