Neuropathic Pain in Female Patients with Fibromyalgia Syndrome: Clinical, Electrodiagnostic and Genetic Aspects.

Objectives: We aimed to explore the potential contribution of small fiber pathology (SFP) and COMT enzyme gene Val/158/Met functional polymorphism to neuropathic pain (NP) in FMS female patients.

Methods: This case-control study was conducted on 60 women with FMS and 60 matched healthy women. All patients were subjected to detailed clinical assessment. Sympathetic skin response (SSR) and cutaneous silent period (CSP) were performed to assess small fiber neuropathy (SFN). Catechol-Omethyl-transferase (COMT) SNP, rs4680 (A/G, missense158Val/Met),) were genotyped for all studied subjects.

Results: FMS patients had significantly longer latency and lower amplitude of foot and hand SSR (P<0.001), with seven patients having unobtainable foot SSR. Also, they had significantly earlier onset latency, longer duration, and more delayed offset latency of CSP (P<0.001, from most of them). Regarding the relation between COMT genotypes and different disease characteristics, patients with A/A genotypes had a statistically significant increase in pain severity scores compared to those with G/G genotypes (P=0.013 for McGill and 0.019 for the visual analogue scale). Moreover, there was a significant increase in NP scores (P=0.004 and 0.001, for pain DETEDT and SFNL, respectively) of A/A and A/G compared to G/G genotypes.

Conclusion: It can be concluded that moderate to severe neuropathic pain was experienced by all the studied patients with fibromyalgia syndrome, and small fiber pathology was suggested to be a significant contributor to neuropathic pain. Moreover, the COMT A/A genotype was found to be associated with the NP as well as pain severity.