Neuropathic pain and symptoms of potential small-fiber neuropathy in fibromyalgic patients: A national on-line survey

Objective: Recent studies have highlighted that about 50% of fibromyalgic patients has a neuropathy of small- and/or large-fibers which could partially explain the puzzling symptoms of fibromyalgia (FM). Our aim was to investigate the estimated prevalence of self-reported neuropathic pain and small-fiber neuropathic symptoms (SFNS) indicative for the presence of small-fiber pathology in FM patients. Methods: A nationwide sample of patients was recruited to participate in an on-line survey. Two groups of patients were considered in post-hoc analysis: those positive (FM+) to the Fibromyalgia Research Criteria (FRC) and those complaining typical symptoms of fibromyalgia without fulfilling the FRC (FM−). Results: We collected data from 854 patients (749 FM+ and 105 FM−). Patients that scored = 50/100 at the Neuropathic Pain Symptoms Inventory (NPSI), indicating severe neuropathic pain, were 57.3% (62.4% in FM+ and 21.0% in FM−). Around 46% of patients presented three or more SFNS that could be suggestive of small fiber pathology, the most frequent being dry eyes/mouth, allodynia, and dyshidrosis. The NPSI score showed significant moderate/strong associations with disability (Spearman's rho = 0.61), pain (rho = 0.66), stiffness level (rho = 0.46), number of painful sites (rho = 0.40), and SFNS (rho = 0.44). Despite the high prevalence of neuropathic pain and other symptoms attributable to potential small and/or large fibers pathology, neurophysiologic investigations were performed in 43.6% of cases and skin punch biopsy only in 1.9% of patients enrolled, as well as the assumption of anti-neuropathic pain drugs (13.2%). Conclusions: Our findings underscore the high estimated prevalence of neuropathic pain and SFNS in FM patients.