Distinguishing fibromyalgia syndrome from small fiber neuropathy: a clinical guide

Abstract

Introduction: Fibromyalgia syndrome (FMS) and small fiber neuropathy (SFN) are distinct pain conditions that share commonalities and may be challenging as for differential diagnosis. Objective: To comprehensively investigate clinical characteristics of women with FMS and SFN to determine clinically applicable parameters for differentiation. Methods: We retrospectively analyzed medical records of 158 women with FMS and 53 with SFN focusing on pain-specific medical and family history, accompanying symptoms, additional diseases, and treatment. We investigated data obtained using standardized pain, depression, and anxiety questionnaires. We further analyzed test results and findings obtained in standardized small fiber tests. Results: FMS patients were on average ten years younger at symptom onset, described higher pain intensities requiring frequent change of pharmaceutics, and reported generalized pain compared to SFN. Pain in FMS was accompanied by irritable bowel or sleep disturbances, and in SFN by paresthesias, numbness, and impaired glucose metabolism (P < 0.01 each). Family history was informative for chronic pain and affective disorders in FMS (P < 0.001) and for neurological disorders in SFN patients (P < 0.001). Small fiber pathology in terms of skin denervation and/or thermal sensory threshold elevation was present in 110/158 (69.7 %) FMS patients and 39/53 (73.6 %) SFN patients. FMS patients mainly showed proximally reduced skin innervation and higher corneal nerve branch densities (p<0.001) whereas SFN patients were characterized by reduced cold detection and prolonged electrical A-delta conduction latencies (P < 0.05). Conclusions: Our data show that FMS and SFN differ substantially. Detailed pain, drug and family history, investigating blood glucose metabolism, and applying differential small fiber tests may help to improve diagnostic differentiation and targeted therapy.

Diagnosing Small Fibre Neuropathy is based on Clearly Defined Criteria, which Require Sequential Application of Various Tools

“…Since clinical experience shows that there is not just one type of pain, one location of pain, one trigger, or one alleviating factor in a patient, it would be desirable to know how many patients combinations of these factors. A sixth point is the discrepancy between the mean time from symptom onset to diagnosis, reported in table 1 for SFN patients as 2.8 years, while the difference between mean age at symptom onset and mean age at diagnosis was 6 years [2] . This discrepancy should be resolved.…”

“…If IENFD is normal, SGNFD may be abnormal. A fourth point is that SFN is not only characterised by acral pain, as mentioned in the introduction [2] . Pain in SFN can have a very variable distribution.…”

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The article by Jänsch et al is excellent but some points should be discussed [2] . The first point is the design of the study.

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