Background & Aims

Fibromyalgia syndrome (FMS) and small fiber neuropathy (SFN) are pain disorders with distinct pathophysiology, but often similar symptoms. Both may also be associated with small fiber pathology (Egenolf et al., 2021). The scientific debate is ongoing whether FMS equals SFN (Oaklander et al.,2013). We aimed to provide an in depth clinical characterization directly comparing FMS with SFN and provide an orientation for clinical use to facilitate diagnostics.

Methods

We retrospectively analyzed data of 158 women with FMS and 53 women with SFN about pain-specific medical history, accompanying symptoms, and additional diseases. We applied standardized pain and anxiety questionnaires, performed blood and small fiber tests: skin punch biopsy, corneal confocal microscopy, quantitative sensory testing (QST), and pain related evoked potentials (PREP).

Results

FMS patients were ca. 10 years younger at symptom onset than SFN patients (p < 0.001). While FMS was characterized by generalized pain, SFN pain was mainly in the feet (p < 0.001). Frequent comorbidities in FMS were migraine (p < 0.01) and depression (p < 0.001), while impaired glucose tolerance was more common in SFN patients (p < 0.05). Irritable bowel (p < 0.001), sleep disturbances (p < 0.001), fatigue (p < 0.001), cognitive impairment (p < 0.001), and stiffness (p < 0.001) were additional symptoms in FMS, whereas SFN patients reported tingling (p < 0.001), numbness (p < 0.01), dyshidrosis (p < 0.01), and sensitivity to touch (p < 0.001). Small fiber tests revealed that proximal skin denervation was more frequent in FMS patients (p < 0.05) and that SFN patients showed a reduced corneal nerve branch density (p < 0.001), more frequent pathological QST results (p < 0.01), and prolonged P1 and N1 latencies in PREP (p < 0.001).

Conclusions

A detailed medical history plays a major role in differentiating FMS and SFN. Pain localization and onset, comorbidities, and accompanying symptoms provide valuable information to distinguish both entities. While small nerve fibers can be affected in both diseases, skin and corneal nerve fiber density, QST, and electrically evoked potentials can provide additional clues for differentiation. Our findings could further be used to develop a screening questionnaire for application in clinical practice to distinguish FMS from SFN.

References

Egenolf N, Zu Altenschildesche CM, Kreß L, Eggermann K, Namer B, Gross F, Klitsch A, Malzacher T, Kampik D, Malik RA, Kurth I, Sommer C, Üçeyler N. Diagnosing small fiber neuropathy in clinical practice: a deep phenotyping study. Ther Adv Neurol Disord 2021;14:17562864211004318.

Oaklander AL, Herzog ZD, Downs HM, Klein MM. Objective evidence that small-fiber polyneuropathy underlies some illnesses currently labeled as fibromyalgia. Pain 2013;154(11):2310-2316.

Presenting Author

Prof. Nurcan Üçeyler

Poster Authors

Sarah Jänsch

Department of Neurology, University of Würzburg, Germany

Lead Author

E-mail

Dimitar Evdokimov

MD

Department of Neurology, University of Würzburg, Germany

Lead Author

E-mail

Nadine Egenolf

Department of Neurology, University Hospital Wuerzburg, Germany

Lead Author

E-mail

Caren Meyer zu Altenschildesche

Department of Neurology, University Hospital Wuerzburg, Germany

Lead Author

E-mail

Luisa Kreß

Dr. med.

University Hospital Würzburg

Lead Author

E-mail

Nurcan Üçeyler

MD

Department of Neurology, University of Würzburg, Germany

Lead Author

E-mail

Topics

  • Models: Musculoskeletal