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

Abstract

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) (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).

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.

Keywords: Diabetes mellitus; Diabetic neuropathy; Motor neuron; Motor unit; Weakness.