Distinguishing fibromyalgia syndrome from small fiber neuropathy: a clinical guide

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.

Cytokine expression profiles in white blood cells of patients with small fiber neuropathy

BACKGROUND

The role of cytokines in the pathophysiology, diagnosis, and prognosis of small fiber neuropathy (SFN) is incompletely understood. We studied expression profiles of selected pro- and anti-inflammatory cytokines in RNA from white blood cells (WBC) of patients with a medical history and a clinical phenotype suggestive for SFN and compared data with healthy controls.

METHODS

We prospectively recruited 52 patients and 21 age- and sex-matched healthy controls. Study participants were characterized in detail and underwent complete neurological examination. Venous blood was drawn for routine and extended laboratory tests, and for WBC isolation. Systemic RNA expression profiles of the pro-inflammatory cytokines interleukin (IL)-1ß, IL-2, IL-8, tumor necrosis factor-alpha (TNF) and the anti-inflammatory cytokines IL-4, IL-10, transforming growth factor beta-1 (TGF) were analyzed. Protein levels of IL-2, IL-8, and TNF were measured in serum of patients and controls. Receiver operating characteristic (ROC)-curve analysis was used to determine the accuracy of IL-2, IL-8, and TNF in differentiating patients and controls. To compare the potential discriminatory efficacy of single versus combined cytokines, equality of different AUCs was tested.

RESULTS

WBC gene expression of IL-2, IL-8, and TNF was higher in patients compared to healthy controls (IL-2: p = 0.02; IL-8: p = 0.009; TNF: p = 0.03) and discriminated between the groups (area under the curve (AUC) ≥ 0.68 for each cytokine) with highest diagnostic accuracy reached by combining the three cytokines (AUC = 0.81, sensitivity = 70%, specificity = 86%). Subgroup analysis revealed the following differences: IL-8 and TNF gene expression levels were higher in female patients compared to female controls (IL-8: p = 0.01; TNF: p = 0.03). The combination of TNF with IL-2 and TNF with IL-2 and IL-8 discriminated best between the study groups. IL-2 was higher expressed in patients with moderate pain compared to those with severe pain (p = 0.02). Patients with acral pain showed higher IL-10 gene expression compared to patients with generalized pain (p = 0.004). We further found a negative correlation between the relative gene expression of IL-2 and current pain intensity (p = 0.02). Serum protein levels of IL-2, IL-8, and TNF did not differ between patients and controls.

CONCLUSIONS

We identified higher systemic gene expression of IL-2, IL-8, and TNF in SFN patients than in controls, which may be of potential relevance for diagnostics and patient stratification.

A translational study: Involvement of miR-21-5p in development and maintenance of neuropathic pain via immune-related targets CCL5 and YWHAE

Neuropathic pain occurs in more than half of the patients suffering from peripheral neuropathies. We investigated the role of microRNA (miR)-21 in neuropathic pain using a murine-human translational approach. We applied the spared nerve injury (SNI) model at the sciatic nerve of mice and assessed the potential analgesic effect of perineurial miR-21-5p inhibitor application. Immune-related targets of miR-21-5p were determined by a qRT-PCR based cytokine and chemokine array. Bioinformatical analysis identified potential miR-21-5p targets interacting with CC-chemokine ligand (CCL)5. We validated CCL5 and tyrosine 3-monooxygenase/tryptophan 5-monooxygenase activation protein (YWHAE), an interaction partner of miR-21-5p and CCL5, by qRT-PCR in murine common peroneal and tibial nerves. Validated candidates were then investigated in white blood cell and sural nerve biopsy samples of patients with focal to generalized pain syndromes, i.e. small fiber neuropathy (SFN), polyneuropathy (PNP), and nerve lesion (NL). We showed that perineurial miR-21-5p inhibition reverses SNI-induced mechanical and heat hypersensitivity in mice and found a reduction of the SNI-induced increase of the pro-inflammatory mediators CCL5 (p < 0.01), CCL17 (p < 0.05), and IL-12ß (p < 0.05) in miR-21-5p inhibitor-treated mice. In silico analysis revealed several predicted and validated targets for miR-21-5p with CCL5 interaction. Among these, we found lower YWHAE gene expression in mice after SNI and perineurial injections of a scrambled oligonucleotide compared to naïve mice (p < 0.05), but this was not changed by miR-21-5p inhibition. Furthermore, miR-21-5p inhibition led to a further increase of the SNI-induced increase in TGFß (p < 0.01). Patient biomaterial revealed different systemic expression patterns of miR-21-5p, with higher expression in SFN and lower expression in NL. Further, we showed higher systemic expression of pro-inflammatory mediators in white blood cells of SFN patients compared to healthy controls. We have conducted a translational study comparing results from animal models to human patients with three different neuropathic pain syndromes. We identified CCL5 as a miR-21 dependent common player in the mouse SNI model and the human painful disease SFN.

Cross-sectional study on patients' understanding and views of the informed consent procedure of a secondary stroke prevention trial

BACKGROUND AND PURPOSE

Improving understanding of study contents and procedures might enhance recruitment into studies and retention during follow-up. However, data in stroke patients on understanding of the informed consent (IC) procedure are sparse.

METHODS

We conducted a cross-sectional study among ischemic stroke patients taking part in the IC procedure of an ongoing cluster-randomized secondary prevention trial. All aspects of the IC procedure were assessed in an interview using a standardized 20-item questionnaire. Responses were collected within 72 h after the IC procedure and analyzed quantitatively and qualitatively. Participants were also asked their main reasons for participation.

RESULTS

A total of 146 stroke patients (65 ± 12 years old, 38% female) were enrolled. On average, patients recalled 66.4% (95% confidence interval = 65.2%-67.5%) of the content of the IC procedure. Most patients understood that participation was voluntary (99.3%) and that they had the right to withdraw consent (97.1%); 79.1% of the patients recalled the study duration and 56.1% the goal. Only 40.3% could clearly state a benefit of participation, and 28.8% knew their group allocation. Younger age, higher graduation, and allocation to the intervention group were associated with better understanding. Of all patients, 53% exclusively stated a personal and 22% an altruistic reason for participation.

CONCLUSIONS

Whereas understanding of patient rights was high, many patients were unable to recall other important aspects of study content and procedures. Increased attention to older and less educated patients may help to enhance understanding in this patient population. Actual recruitment and retention benefit of an improved IC procedure remains to be tested in a randomized trial.

Diagnosing small fiber neuropathy in clinical practice: a deep phenotyping study

Background and aims

Small fiber neuropathy (SFN) is increasingly suspected in patients with pain of uncertain origin, and making the diagnosis remains a challenge lacking a diagnostic gold standard.

Methods

In this case-control study, we prospectively recruited 86 patients with a medical history and clinical phenotype suggestive of SFN. Patients underwent neurological examination, quantitative sensory testing (QST), and distal and proximal skin punch biopsy, and were tested for pain-associated gene loci. Fifty-five of these patients additionally underwent pain-related evoked potentials (PREP), corneal confocal microscopy (CCM), and a quantitative sudomotor axon reflex test (QSART).

Results

Abnormal distal intraepidermal nerve fiber density (IENFD) (60/86, 70%) and neurological examination (53/86, 62%) most frequently reflected small fiber disease. Adding CCM and/or PREP further increased the number of patients with small fiber impairment to 47/55 (85%). Genetic testing revealed potentially pathogenic gene variants in 14/86 (16%) index patients. QST, QSART, and proximal IENFD were of lower impact.

Conclusion

We propose to diagnose SFN primarily based on the results of neurological examination and distal IENFD, with more detailed phenotyping in specialized centers.

[Pain prevention: what is in the pipeline?]

Approximately 10% of the German population report chronic pain that has at least a moderate influence on everyday life. For instance, patients in Germany often experience an oversupply of diagnostics and therapy when suffering from mild back pain, while the care of patients with severe, chronic pain remains insufficient. Multimodal and interdisciplinary therapies are generally too seldomly used. Potentially preventive procedures are insufficiently investigated and used in current clinical practice and little is known about the mechanisms underlying chronification processes. In Germany, pain is still largely neglected in current clinical and basic science, as well as research funding. Furthermore, existing projects are often insufficiently connected with each other, thereby missing the unique opportunity of building synergies. To improve medical pain care and to enable participation in activities of daily life with the maximum radius, interdisciplinary clinical programs and cross-linking of basic and clinical research is necessary. The main objectives are to: (1) Strengthen basic research to investigate the underlying mechanisms of pain development and maintenance as well as of chronification processes; (2) improve patient care by adequate application of diagnostic, therapeutic, and preventive procedures; (3) consolidate interdisciplinarity in pain research and patient care; (4) maintain participation of patients in social and in everyday life; and (5) achieve and maintain high quality standards in pain patient care. The following article provides an overview of the measures and advances currently being taken in pain research in Germany to close the above-mentioned gaps. The focus lies on current and future developments in the field of pain prevention.

Patient-derived in vitro skin models for investigation of small fiber pathology

Objective

To establish individually expandable primary fibroblast and keratinocyte cultures from 3‐mm skin punch biopsies for patient‐derived in vitro skin models to investigate of small fiber pathology.

Methods

We obtained 6‐mm skin punch biopsies from the calf of two patients with small fiber neuropathy (SFN) and two healthy controls. One half (3 mm) was used for diagnostic intraepidermal nerve fiber density (IENFD). From the second half, we isolated and cultured fibroblasts and keratinocytes. Cells were used to generate patient‐derived full‐thickness three‐dimensional (3D) skin models containing a dermal and epidermal component. Cells and skin models were characterized morphologically, immunocyto‐ and ‐histochemically (vimentin, cytokeratin (CK)‐10, CK 14, ki67, collagen1, and procollagen), and by electrical impedance.

Results

Distal IENFD was reduced in the SFN patients (2 fibers/mm each), while IENFD was normal in the controls (8 fibers/mm, 7 fibers/mm). Two‐dimensional (2D) cultured skin cells showed normal morphology, adequate viability, and proliferation, and expressed cell‐specific markers without relevant difference between SFN patient and healthy control. Using 2D cultured fibroblasts and keratinocytes, we obtained subject‐derived 3D skin models. Morphology of the 3D model was analogous to the respective skin biopsy specimens. Both, the dermal and the epidermal layer carried cell‐specific markers and showed a homogenous expression of extracellular matrix proteins.

Interpretation

Our protocol allows the generation of disease‐specific 2D and 3D skin models, which can be used to investigate the cross‐talk between skin cells and sensory neurons in small fiber pathology.

Pain-associated Mediators and Axon Pathfinders in Fibromyalgia Skin Cells

Objective.

To investigate whether the expression of cytokine, nociception-associated ion channel, and axon guidance genes in patients with skin cell fibromyalgia syndrome (FMS) differs from healthy controls, potentially contributing to pain and small-fiber degeneration in FMS.

Methods.

We prospectively recruited 128 patients and 26 healthy controls. All study participants underwent neurological examination, and a skin punch biopsy was obtained from the lateral calf and thigh. Skin samples were processed to histologically determine intraepidermal nerve fiber density (IENFD) and for primary fibroblast and keratinocyte cell cultures. Gene expression of selected pro- and antiinflammatory cytokines, nociception-associated ion channels, and axon guidance cues was assessed with quantitative real-time PCR.

Results.

In fibroblasts, transforming growth factor–ß1 (TGF-ß1) gene expression was higher in patients with FMS compared to controls (calf and thigh: p < 0.001). Also, expression was higher in patients than in controls for these variables: hyperpolarization-activated cyclic nucleotide-gated ion channel 2 (calf: p < 0.01), ephrin-A4 (EFNA4; calf: p < 0.05, thigh: p < 0.001), and ephrin receptor-A4 (EPHA4; thigh: p < 0.05). In keratinocytes, interleukin 10 gene expression was higher in patients with FMS than in controls (thigh: p < 0.05). While no intergroup difference was found for nociception-associated ion channels, EFNA4 and EPHA4 (calf: p < 0.01 each) expression was higher in patients with FMS than in controls. Axon guide expression did not correlate with IENFD.

Conclusion.

In FMS, skin cells may contribute to cutaneous nociception by differentially expressing membrane-bound and soluble pain mediators and axon pathfinders.