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

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).

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.

In both muscles, patients with DPN had significantly reduced motor unit number estimates (MUNEs) (ΔTA ∼45%; ΔFDI ∼30%), compound muscle action potentials (CMAPs) (ΔTA ∼30%; ΔFDI ∼20%), and mean firing rates were reduced (ΔTA ∼15%; ΔFDI ∼15%) compared to controls (p<0.05). For the TA, patients with DPN had larger mean surface motor unit potentials (SMUPs) (ΔTA ∼40%; p<0.05), whereas in the FDI no differences were found (p>0.05).

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.

DQEMG may be a clinically useful technique in identifying the presence and severity of neuromuscular pathophysiology and tracking disease progression in DPN.