Motor Neuropathy in Diabetes

Motor nerves are impaired in distal symmetric polyneuropathy (DSPN) to the same degree as sensory nerves based on nerve conduction studies. However, motor neuropathy becomes clinically apparent only in later stages of DSPN. Motor neuropathy is characterized by muscle weakness and muscular atrophy which may lead to postural instability, impaired ambulation, and increased morbidity. Motor involvement may go unnoticed, as early motor symptoms and deficits are not included in the standardized assessment for DSPN. Muscle weakness follows the same topographical distribution as sensory symptoms and deficits seen in DSPN with a symmetrical and distal distribution presenting as weakness at the toes followed by weakness at the ankle and knee. The diagnosis is based on a combination of clinical tests and nerve conduction studies. Several other methods can be applied to assess muscle size and quality, including imaging techniques and muscle biopsies; however, these methods are mainly used for research purposes. Currently, there are no specific treatments for motor neuropathy, but recent evidence indicates strength benefits from physical training of motor dysfunction in individuals with DSPN. In this chapter, we will be discussing all aspects of motor neuropathy, including clinical presentation, pathophysiology, muscle strength, diagnostic tools, functional consequences of motor impairment, and the effects of exercise.