Pain Characteristics do not Distinguish Fibromyalgia Patients with Abnormal Skin Biopsy (P5.069)

OBJECTIVE: To determine whether pain characteristics can distinguish between fibromyalgia patients who have abnormal skin biopsy and/or SNAP amplitudes. BACKGROUND: Patients (n=165) with fibromyalgia were assessed for differences in pain characteristics as a function of sural/medial plantar SNAP amplitudes and intra-epidermal nerve fiber densities (IENF). DESIGN/METHODS: Fibromyalgia diagnosis was verified by the American College of Rheumatology 2010 Fibromyalgia criteria. All patients underwent standard nerve conduction studies including medial plantar sensory conductions. Each patient completed a Short-Form McGill Pain Questionnaire as part of their evaluation. RESULTS: The greatest correlation existed between medial plantar SNAP amplitude and IENF density at the calf (rho=0.45; p<0.0001) although correlation also existed between sural amplitude and IENF density at the calf (rho=0.38; p<0.0001). There was no significant correlation between medial plantar or sural SNAP amplitudes and IENF density at the thigh (rho=0.10, p=0.25; rho=0.06, p=0.51). Overall pain characteristics did not distinguish either skin biopsy findings or SNAP amplitudes although some characteristics approached significance. Patients with reduced IENF at the calf had higher total pain scores than patients with normal distal IENF but this difference was not significant. The characteristic descriptions of “sharp” and “splitting” pain were most likely to distinguish these patients while characteristics of “tenderness”, “aching” and “throbbing” were least likely to be distinctive. Heaviness was significantly more often described in patients with reduced IENF at the thigh (p<0.05). Pain characteristics did not distinguish patients with preserved versus reduced SNAP amplitudes. CONCLUSIONS: Reduced IENF in patients who fulfilled the 2010 ACR criteria for FM had pain characteristics that did not clearly distinguish them from patients with normal IENF. Although a correlation existed between IENF density and SNAP amplitudes, pain characteristics did not distinguish those patients with reduced SNAPs. These data suggest that pain is nonspecific in the detection of small fiber neuropathy in fibromyalgia patients. Study Supported by: Disclosure: Dr. Lawson has nothing to disclose. Dr. Grewal has nothing to disclose. Dr. Hackshaw has nothing to disclose. Dr. Mongiovi has nothing to disclose.