Neuropathic Pain in Female Patients With Fibromyalgia: Clinical, Electrodiagnostic, and Genetic Aspects

To explore the potential contribution of small fiber pathology (SFP) and COMT enzyme gene Val/158/Met functional polymorphism to neuropathic pain (NP) in female fibromyalgia (FM) patients.

This case-control study was conducted on 60 women with FM 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-O-methyl-transferase (COMT) SNP, rs4680 (A/G, missense158Val/Met) were genotyped.

FM patients had significantly longer latency and lower amplitude of foot and hand SSR ( P <0.001), with 7 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 with those with G/G genotypes ( P =0.013 for McGill and 0.019 for the Visual Analog 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 with G/G genotypes.

Moderate to severe neuropathic pain was experienced by all the studied patients with FM, 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 and pain severity.