Background/Purpose: Small fiber neuropathy (SFN), a polyneuropathy (PNP) affecting A-delta and C-fibers has been described in patients with fibromyalgia (FM). Different patterns of small fiber damage may characterize distinct subtypes of FM. We aimed to investigate the value of detecting different degrees of SFN in patients diagnosed with FM.

Methods: Consecutive patients who were treated for pain exacerbation of FM at a university specialized tertiary center were included in the study after informed consent. Patients had to fulfil the 2016 ACR diagnostic criteria for FM and other inflammatory rheumatic musculoskeletal diseases (RMD) were excluded. The rheumatological therapy included pain pharmacotherapy, balneophysical treatment, physiotherapy and occupational therapy. All patients underwent a careful rheumatologic and neurologic physical clinical examination including a Schirmer-Test for dry eyes and were asked to fill out questionnaires, in which data on pain, depression, neuropathic symptoms, sleep quality, daytime sleepiness, fatigue, and quality of life were assessed. Thereafter small fiber tests were performed in the neurologic department including a skin punch biopsy on the upper and lower leg and a corneal confocal microscopy (CCM).

Results: Overall, 93 patients (86 females, 92.5%, mean age 54±10.1, mean disease duration 4.9±5.3 years) were included, 25 received anticonvulsants (26.9%) and 15 opioids (16.1%) for pain treatment. Intraepidermal nerve fiber density (IENFD) as detected by skin biopsy was reduced in 58 patients (62.4%), 43 of whom (74.1%) had reduced IENFD at both proximal and distal sites. CCM showed pathologic findings in 18 patients with reduced IENFD at any site (31%) and in 8 with normal IENFD (22.9%), with dry eyes being present in 13 (22.4%) and 6 (17.1%) of those patients, respectively. There was no difference in pain, depression, neuropathic symptoms, sleep quality, daytime sleepiness, fatigue, or quality of life scores between groups (Table).

Conclusion: In this FM population with high disease burden and indication for inpatient therapy, small fiber pathology as found by skin biopsies and CCM was present in more than two third of the FM patients suggesting that there are subgroups. However, there were no significant clinical differences between patients with and without SFN. Further analysis should explore, whether both subgroups differ in their long-term outcome after the inpatient treatment.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/value-of-small-fiber-neuropathy-in-fibromyalgia-patients-in-a-rheumatological-setting/