Pain and small fiber pathology in men with fibromyalgia syndrome.

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Small fiber pathology may be involved in the pathophysiology of pain in women with fibromyalgia syndrome (FMS). This prospective single-center case-control study provides detailed pain phenotyping and small fiber pathology data in a cohort of men with FMS on a morphological and functional level. Forty-two men with FMS underwent a comprehensive pain-related interview and neurological examination, a questionnaire and neurophysiological assessment, and specialized small fiber tests: skin punch biopsy, quantitative sensory testing including C-tactile afferents, and corneal confocal microscopy. Data were compared with those of healthy male controls. Men with FMS reported generalized and permanent pain with additional pain attacks and a mostly pressing pain character. Intraepidermal nerve fiber density was reduced at ≥1 biopsy site in 35 of 42 (83%) men with FMS (controls: 32/65, 49%). Compared with male controls, men with FMS had elevated cold (P < 0.05) and warm detection thresholds (P < 0.001) and an increased mechanical pain threshold (P < 0.05) as well as an impairment of C-tactile afferents (P < 0.05). Corneal nerve fiber density was lower in male patients with FMS vs healthy men (P < 0.01). Male FMS patients with pathological skin innervation at ≥1 biopsy site compared with those with normal skin innervation had a higher clinical Widespread Pain Index (P < 0.05) indicating an association between the severity of cutaneous denervation and symptom load. We show a distinct pain phenotype and small nerve fiber dysfunction and pathology in male patients with FMS. These findings may have implications for the diagnosis and management of men with FMS.