Motor Unit Characteristics and Proprioceptive Deficits of the Upper Limb in Patients with Type II Diabetes
Gulley Cox, Lauren I.
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Persons with Type II Diabetes (pwT2D) are at risk of developing nerve disorders that result in sensorimotor dysfunction, particularly of the hands and feet. Neuromuscular and proprioceptive dysfunction associated with diabetes are two areas needing more research to determine their contribution to T2D related functional impairments. Most work in these two areas has been focused on deficits in the lower limb. Proprioceptive dysfunction in the upper limb associated with T2D has yet to be characterized. Similarly, evaluation of neuromuscular dysfunction in the upper limb is lacking. Knowing that peripheral neuropathy (PN) affects the hands in addition to the feet and legs, this is an area that should be explored. Thus, the purpose of this study is to examine the neuromuscular and proprioceptive effects on the upper limb in pwT2D. This will be achieved by a) evaluating the effects of T2D on kinematic performance of a reach-to-pinch task; b) characterizing T2D associated motor unit properties in five upper limb muscles; and c) determine if observed alterations to motor unit characteristics are length-dependent in the upper limb. Three groups were recruited: young, healthy controls (group 1, 18-30 years old), T2D group (group 2, 60+ years old with established T2D), and an age- and sex-matched Control group without T2D (group 3, 60+ years old without a history of diabetes). Group 1 underwent sensory evaluation (tactile and vibrotactile sensation) and neuromuscular evaluation (nerve stimulation and motor evaluation) and served as an approach validation. Groups 2 and 3 underwent blood sugar and cholesterol testing, sensory evaluation (tactile and vibrotactile sensation), neuromuscular evaluation (nerve stimulation and motor evaluation), and proprioceptive evaluation (reach-to-pinch task). Overall, sensory thresholds did not differ between T2D and Control participants. CMAP amplitude and MUNIX were significantly reduced in Control participants compared to pwT2D. Additionally, mean pinch location error was significantly worse for pwT2D in addition to differences in wrist extension/flexion (ex/fl), wrist abduction/adduction (ab/ad), CMC1 ab/ad, MCP2 ex/fl, and MCP2 ab/ad angular joint trajectories and index finger and hand transport trajectories between the two groups. These findings suggest proprioception of the upper extremity is altered in pwT2D and they exhibit a unique aperture position and aiming strategy during a reach-to-pinch task. These findings help to understand proprioceptive and neuromuscular function of the upper limb in pwT2D, with implications to early identify patients who may need medical and/or lifestyle intervention.