Small Fiber Neuropathy in Patients Meeting Diagnostic Criteria for Fibromyalgia

Introduction: The cause for fibromyalgia (FM) is unknown and diagnostic criteria can be nonspecific. Many patients with FM have nonspecific sensory symptoms consistent with a neuropathic process. Previous studies have shown that a significant percentage of patients diagnosed with FM have small fiber neuropathy (SFN) based on decreased intraepidermal nerve fiber density (IENFD) on according to punch skin biopsy testing. The purpose of this study was to demonstrate that punch skin biopsy testing is an effective way to identify SFN and its underlying causes in patients previously diagnosed with FM. Methods: We studied 56 patients referred to peripheral nerve disease centers for evaluation of neuropathic pain who met the diagnostic criteria for FM. All underwent punch skin biopsy testing. If SFN was detected, patients underwent further laboratory testing to look for a potential cause for the neuropathy. Results: Thirty-four of 56 patients (61%) had SFN, as indicated by reduced IENFD. Twenty-four of 34 patients with SFN (71%) had laboratory evidence that revealed an underlying etiology for the SFN. Conclusions: More than half of the patients presenting with neuropathic pain and who met diagnostic criteria for FM had SFN detected by skin biopsy testing. A potential cause for neuropathy was identified in 71% of the patients with SFN. Skin biopsy testing to look for SFN is a very high-yield test in patients with FM who have neuropathic pain symptoms. Diagnosing SFN can facilitate the identification of potential causes for the neuropathy and alter their management.