T84. Reduced amplitudes of pain-related evoked potentials in patients with neuropathic pain and normal small nerve fiber function and morphology

Abstract

Cortical pain-related evoked potentials (PREP) are elicited by activation of the Aδ-fibers using cutaneous electrical stimulation and objectively reflect the Aδ-pathways. PREP were applied in an unselected patient population with acral neuropathic pain to explore its diagnostic usefulness in detecting small fiber impairment compared to quantitative sensory test (QST) and skin punch biopsy. Thirty-two patients (13 male and 19 female, median age 50 years, range 26–83) suffering from acral neuropathic pain were examined clinically and with nerve conduction studies, QST, skin punch biopsy and PREP. The study cohort consisted of 16 patients with small fiber neuropathy (SFN), 18 patients with mixed fiber neuropathy (MFN, i.e. large and small fiber neuropathy), and 8 patients with acral neuropathic pain without signs of a large fiber neuropathy or SFN. QST and skin biopsy were pathological in terms of elevated thermal thresholds and reduced distal skin innervation in patients with SFN and MFN, while patients with acral neuropathic pain had normal findings. PREP was the only method showing a pathological finding, namely reduced peak-to-peak amplitudes also in patients with acral neuropathic pain (p < 0.05). PREP was the only method revealing small fiber dysfunction in patients suffering from acral neuropathic pain with otherwise normal QST and skin biopsy. As a non-invasive test giving reproducible results, PREP may contribute to the diagnostic portfolio of small fiber tests in patients with neuropathic pain.