Length dependent loss of motor axons and altered motor unit properties in human diabetic polyneuropathy

Objective: To assess the number and properties of motor units in an upper and lower limb muscle (tibialis anterior [TA] and first dorsal interosseous [FDI]) in human diabetic polyneuropathy (DPN) using decomposition- based quantitative electromyography (DQEMG). Methods: DQEMG protocols were performed in the TA and FDI of 12 patients with confirmed diabetes mellitus and associated DPN, as well as 12 age-matched control participants. Maximal dorsiflexion strength was also assessed using a dynamometer. Results: In both muscles, patients with DPN had significantly reduced motor unit number estimates (MUNEs) (Delta TA similar to 45%; Delta FDI similar to 30%), compound muscle action potentials (CMAPs) (Delta TA similar to 30%; Delta FDI similar to 20%), and mean firing rates were reduced (Delta TA similar to 15%; Delta FDI similar to 15%) compared to controls (p < 0.05). For the TA, patients with DPN had larger mean surface motor unit potentials (SMUPs) (Delta TA similar to 40%; p < 0.05), whereas in the FDI no differences were found (p > 0.05). Conclusions: DPN may result in motor unit loss, remodeling, and altered firing rate patterns. The magnitude of changes in the neuromuscular properties of DPN patients are muscle dependent and reflect a length-dependent disease progression. Significance: DQEMG may be a clinically useful technique in identifying the presence and severity of neuromuscular pathophysiology and tracking disease progression in DPN. (C) 2013 International Federation of Clinical Neurophysiology. Published by Elsevier Ireland Ltd. All rights reserved.