Fibromyalgia Syndrome and Small-Fiber Neuropathy: Comment on the Article by Caro and Winter

A systematic review and meta-analysis of the prevalence of small fiber pathology in fibromyalgia: Implications for a new paradigm in fibromyalgia etiopathogenesis

OBJECTIVES

Fibromyalgia is a condition which exhibits chronic widespread pain with neuropathic pain features and has a major impact on health-related quality of life. The pathophysiology remains unclear, however, there is increasing evidence for involvement of the peripheral nervous system with a high prevalence of small fiber pathology (SFP). The aim of this systematic literature review is to establish the prevalence of SFP in fibromyalgia.

METHODS

An electronic literature search was performed using MEDLINE, EMBASE, PubMed, Web of Science, CINAHL and the Cochrane Library databases. Published full-text, English language articles that provide SFP prevalence data in studies of fibromyalgia of patients over 18years old were included. All articles were screened by two independent reviewers using a priori criteria. Methodological quality and risk of bias were evaluated using the critical appraisal tool by Munn et al. Overall and subgroup pooled prevalence were calculated by random-effects meta-analysis with 95% CI.

RESULTS

Database searches found 935 studies; 45 articles were screened of which 8 full text articles satisfied the inclusion criteria, providing data from 222 participants. The meta-analysis demonstrated the pooled prevalence of SFP in fibromyalgia is 49% (95% CI: 38-60%) with a moderate degree of heterogeneity, (I²= 68%). The prevalence estimate attained by a skin biopsy was 45% (95% CI: 32-59%, I²= 70%) and for corneal confocal microscopy it was 59% (95% CI: 40-78%, I²= 51%).

CONCLUSION

There is a high prevalence of SFP in fibromyalgia. This study provides compelling evidence of a distinct phenotype involving SFP in fibromyalgia. Identifying SFP will aid in determining its relationship to pain and potentially facilitate the development of future interventions and pharmacotherapy.

Fibromyalgia syndrome and small fiber, early or mild sensory polyneuropathy

INTRODUCTION

Pain mechanisms in fibromyalgia syndrome (FMS) are not clearly understood. Growing evidence appears to suggest a role for small fiber polyneuropathy (SFPN) in some FMS patients, as measured by epidermal nerve fiber density (ENFD). We aimed to better characterize and distinguish the subset of patients with both fibromyalgia and small fiber, early or mild sensory polyneuropathy (FM-SFSPN).

METHODS

155 FMS patients with neuropathic symptoms completed a Short Form McGill Questionnaire and visual analog scale in addition to having skin biopsies, nerve conduction studies (NCS), and serologic testing.

RESULTS

Sural and medial plantar (MP) response amplitudes correlated with ENFD, with markers of metabolic syndrome being more prevalent in this subset of patients. Pain intensity and quality did not distinguish patients.

DISCUSSION

The FM-SFSPN subset of patients may be identified through sural and MP sensory NCS and/or skin biopsy but cannot be identified by pain features and intensity. Muscle Nerve 58: 625-630, 2018.

Reduction of Intraepidermal Nerve Fiber Density (IENFD) in the skin biopsies of patients with fibromyalgia: a controlled study

OBJECTIVES

Fibromyalgia (FM) is one of the most common chronic pain syndromes. Various pathogenetic mechanisms have been implicated but none is proven. Our scope was to determine if Intraepidermal Nerve Fiber Density (IENFD) is reduced in the skin of FM patients, as observed in patients with painful small fiber sensory neuropathy (SFSN).

DESIGN, SETTING AND PARTICIPANTS

We prospectively studied 46 FM patients (5 men and 41 women), aged 29 to 76 (mean: 52.5) years, diagnosed according to the ACR 2010 criteria, and 34 controls (18 women and 16 men) aged 19 to 84 (mean: 31.7) years. IENFD was measured using published guidelines and immune markers were sought immunocytochemically. In 30 FM patients, pain intensity was assessed with the Neuropathic Pain Symptom Inventory (NPSI), a scale validated for neuropathic pain.

RESULTS

15 of 46 (32.6%) FM patients had reduced IENFD [range: 0.6-12.5 fibers/mm (mean: 4.83 SD: 2.5)], compared to healthy controls [2.8-11.5 fibers/mm (mean: 7.35, SD: 1.85)] (p<0.0001). No significant correlation was noticed between NPSI scores and IENFD. No difference in the Langerhans cells, the major Antigen Presenting Cells (APCs) in the epidermis, or in IL-6 staining, was noted between FM and controls. IENFD was equally reduced in a subset of FM patients who also had another autoimmune disease.

CONCLUSION

This is one of the largest series of FM patients demonstrating a significant reduction of IENFD in their skin biopsies. The findings indicate that in a subset of FM patients, the pain syndrome is, at least partially, of neuropathic origin. Skin biopsy may prove a useful tool and a potential biomarker in future studies of FM patients.