[Fibromyalgia syndrome: A disease of the small nerve fibers?]. / Fibromyalgiesyndrom : Eine Erkrankung der kleinen Nervenfasern?

Fibromyalgia syndrome (FMS) is characterized by chronic widespread pain and additional associated symptoms, such as fatigue, sleep disturbances and depressive moods. The pathophysiology of pain in FMS is unclear. In recent years, an involvement of the thinly myelinated A-delta and the unmyelinated C-nerve fibers has been reported in FMS patients. Independent research groups published consistent objective and multidimensional findings of damage to these small nerve fibers, such as disturbances of fiber function, electrical properties and morphological changes. All these alterations are not specific for FMS; however, they were described for the first time in subgroups of FMS patients. While the reasons for this small fiber pathology and its contribution to FMS pain are still unclear, a new research field has now been opened that will focus on uncovering the underlying pathophysiology. This review article summarizes these new findings and discusses the significance for the understanding of FMS.

Small fiber neuropathies.

PURPOSE OF REVIEW: This article reviews the clinical, neurophysiologic, and neuropathologic findings in patients presenting with small fiber neuropathies. Emphasis is placed on recent updates to the literature, but also on understanding the differential diagnosis and initial evaluation of patients with small fiber neuropathy. RECENT FINDINGS: There have been several updates in the literature about diseases associated with small fiber neuropathy. First, treatment-induced neuropathy in diabetes mellitus is an iatrogenic small fiber neuropathy linked to overly rapid correction in blood glucose levels in the setting of chronic hyperglycemia. Second, several novel mutations to sodium channels have been identified in patients presenting with idiopathic small fiber neuropathy that may significantly alter our understanding and future treatment of small fiber neuropathy. Third, antibodies against voltage-gated potassium channels appear to be associated with a much higher incidence of pain than would be expected, although the mechanism has not been established. Fourth, the link between glucose dysregulation, metabolic syndrome, and neuropathy continues to grow. Finally, several other disorders, including postural orthostatic tachycardia syndrome, have been postulated to be associated with small fiber neuropathies. SUMMARY: Small fiber neuropathies are a heterogeneous group of disorders that may present with a variety of sensory or autonomic symptoms. Recent reports highlight a number of new causes of small fiber neuropathy that continue to reduce the number of remaining idiopathic cases.

Evidence of abnormal epidermal nerve fiber density in fibromyalgia: clinical and immunologic implications.

OBJECTIVE: A subset of patients with fibromyalgia (FM) exhibit a large fiber demyelinating peripheral polyneuropathy akin to that seen in chronic inflammatory demyelinating polyneuropathy (CIDP). It has been suggested that this demyelinating process is likely to be immune mediated. Because it is known that similar large fiber neuropathic lesions may be associated with a cutaneous small fiber neuropathy, we sought to determine the prevalence of small fiber neuropathy, as measured by epidermal nerve fiber density (ENFD), in a series of patients with FM and clinically healthy control subjects. METHODS: Forty-one consecutive patients with FM and 47 control subjects underwent a 3-mm punch skin biopsy at the proximal thigh and distal leg near the ankle, for analysis of the ENFD. Patients with FM who had clinical evidence of a disorder known to be associated with small fiber neuropathy were excluded. The patients with FM also underwent pinwheel testing and vibratory testing for hypesthesia and serologic testing for a series of cytokine, circulating immune complex, and complement measurements. RESULTS: All patients with FM had evidence of stocking hypesthesia. The ENFD of patients with FM was lower than that of control subjects at both the calf (mean ± SD 5.8 ± 2.8 versus 7.4 ± 1.9; P = 0.0002) and thigh (9.3 ± 3.2 versus 11.3 ± 2.0; P = 0.0007). There was an inverse correlation between calf ENFD and age at the time of skin biopsy in patients with FM (r = -0.29, P = 0.03) but not in control subjects; however, analysis of covariance showed that this relationship could not be explained by aging alone. Serologic evaluation showed an inverse correlation between calf ENFD in patients with FM and the interleukin-2 receptor (IL-2R) level (r = -0.28, P = 0.04). However, an inverse correlation between thigh ENFD and serum IL-2R levels did not reach significance (P = 0.08). Analysis of thigh-to-calf ENFD ratios suggested that the ENFD decline in FM is affected by both a diffuse and a length-dependent process. CONCLUSION: The calf and thigh ENFD in patients with FM is significantly diminished compared with that in control subjects. Advancing age alone cannot explain this finding. Calf ENFD was inversely correlated, although weakly, with serum levels of IL-2R. These findings suggest that small fiber neuropathy is likely to contribute to the pain symptoms of FM; that pain in this disorder arises, in part, from a peripheral immune-mediated process; and that measurement of ENFD may be a useful clinical tool in FM.

Childhood steroid-responsive acute erythromelalgia with axonal neuropathy of large myelinated fibers: a dysimmune neuropathy?

A 12-year-old girl developed acute erythromelalgia of distal extremities. Physical, imaging and laboratory examinations failed to find an infective, systemic autoimmune, metabolic, endocrine, and vascular origin. The severe pain and allodynia indicated small-fiber neuropathy but muscle weakness suggested an involvement of large myelinated nerve fibers. This was confirmed by electrophysiological testing. High-dose then slowly tapered methylprednisolone resulted in rapid remission of painful erythromelalgia and complete electrophysiological recovery. Our case may suggest an additional variant to recently described steroid-responsive erythromelalgia with small-fiber axonopathy and may denote a transitory variant to Guillain-Barré syndrome or chronic dysimmune neuropathies.

Clinical and histopathologic features and immunologic variables in patients with severe chilblains. A study of the relationship to lupus erythematosus.

We investigated 33 patients affected with chilblain lesions following a persisting course of more than 1 month. We focused on the incidence of an underlying connective tissue disease, mostly lupus erythematosus (LE), and we analyzed features of idiopathic chilblains compared with those of chilblain lesions associated with connective tissue disease. We also carried out a prospective follow-up of patients. Eleven patients included in the study were free of any clinical and/or laboratory abnormality suggestive of connective tissue disease, while 22 of 33 patients showed 1 or several abnormalities raising suspicion for connective tissue disease, and among them 8 had a diagnosis of systemic lupus erythematosus (SLE) established at initial evaluation based on the American College of Rheumatology revised criteria. The comparative analysis of patients with idiopathic chilblains and patients with chilblains associated with LE showed that female sex and persistence of lesions beyond cold seasons were significantly associated with chilblain LE. Histopathologic studies of chilblain lesions did not reveal features typical of LE in any case, but revealed a higher incidence of a deep perisudoral infiltrate in idiopathic chilblains. In patients showing signs of connective tissue disease, positive cutaneous immunofluorescence was correlated with the presence of circulating antinuclear antibodies. Two patients had an ascertained diagnosis of SLE with severe manifestations during prospective follow-up, requiring treatment with oral steroids in both cases. Chilblains following a chronic course may reveal connective tissue disease, and patients affected with chilblains associated with autoimmune abnormalities may develop severe SLE. Accordingly, long-term follow-up of these patients is warranted.

Secondary erythermalgia associated with an autoimmune disorder of undetermined significance.

A 50-year-old female patient is described with an acquired, persisting and yet incurable erythermalgia featured by symmetric burning pain and red congestion of the extremities secondary to cutaneous vasculitis. A weakly positive antinuclear antibody titer and high titers of antibodies against gastric parietal mucosa cells pointed to an underlying but unclassifiable autoimmune disorder. It is concluded that histopathology of lesional skin contributes to the differential diagnosis of primary and secondary erythermalgia.