Neuropathic pain is associated with increased nodal persistent Na⁺ currents in human diabetic neuropathy

Abstract Peripheral nerve injury alters function and expression of voltage gated Na⁺ channels on the axolemma, leading to ectopic firing and neuropathic pain/paresthesia. Hyperglycemia also affects nodal Na⁺ currents, presumably due to activation of polyol pathway and impaired Na⁺–K⁺ pump. We investigated changes in nodal Na⁺ currents in peripheral sensory axons and their relation with pain in human diabetic neuropathy. Latent addition using computerized threshold tracking was used to estimate nodal persistent Na⁺ currents in radial sensory axons of 81 diabetic patients. Of these, 36 (44%) had chronic neuropathic pain and severe paresthesia. Compared to patients without pain, those with pain had greater nodal Na⁺ currents (p = 0.001), smaller amplitudes of sensory nerve action potentials (SNAP) (p = 0.0003), and lower hemoglobin A1c levels (p = 0.006). Higher axonal Na⁺ conductance was associated with smaller SNAP amplitudes (p = 0.03) and lower hemoglobin A1c levels (p = 0.008). These results suggest that development of neuropathic pain depends on axonal hyperexcitability due to increased nodal Na⁺ currents associated with structural changes, but the currents could also be affected by the state of glycemic control. Our findings support the view that altered Na⁺ channels could be responsible for neuropathic pain/paresthesia in diabetic neuropathy.