Invited Review: Neuromuscular consequences of spinal cord injury: New mechanistic insights and clinical considerations
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Abstract
The spinal cord facilitates communication between the brain and the body, containing intrinsic systems that work with lower motor neurons (LMNs) to manage movement. Spinal cord injuries (SCIs) can lead to partial paralysis and dysfunctions in muscles below the injury. While traditionally this paralysis has been attributed to disruptions in the corticospinal tract, a growing body of work demonstrates LMN damage is a factor. Motor units, comprising the LMN and the muscle fibers with which they connect, are essential for voluntary movement. Our understanding of their changes post-SCI is still emerging, but the health of motor units is vital, especially when considering innovative SCI treatments like nerve transfer surgery. This review seeks to collate current literature on how SCI impact motor units and explore neuromuscular clinical implications and treatment avenues. SCI reduced motor unit number estimates, and surviving motor units had impaired signal transmission at the neuromuscular junction, force-generating capacity, and excitability, which have the potential to recover chronically, yet the underlaying mechanisms are unclear. Furthermore, electrodiagnostic evaluations can aid in assessing the health lower and upper motor neurons, identify suitable targets for nerve transfer surgeries, and detect patients with time sensitive injuries. Lastly, many electrodiagnostic abnormalities occur in both chronic and acute SCI, yet factors contributing to these abnormalities are unknown. Future studies are required to determine how motor units adapt following SCI and the clinical implica-tions of these adaptations.
Objectives: The objectives of this activity are to enable the reader to: 1) Understand how motor unit number estimations change following spinal cord injury, how these relate to compound muscle action potential amplitudes, and how this impacts electrodiagnostic findings and interpretation; (2) Understand now the changes in motor unit properties after spinal cord injuries impact clinical and electrodiagnostic results; (3) Incorporate into clinical practice information about damage to lower motor neurons at and below the level of spinal cord injury, and how this impacts prognosis.
ACCREDITATION STATEMENT The AANEM is accredited by the Accreditation Council for Continuing Medical Education (ACCME) to provide continuing medical education for physicians.
CREDIT DESIGNATION The AANEM is accredited by the American Council for Continuing Medical Education (ACCME) to providing continuing education for physicians. AANEM designates this Journal-based CME activity for a maximum of 1.0
AMA PRA Category 1 Credit™. Physicians should claim only the credit commensurate with the extent of their participation in the activity. Credit expires 3/11/2027.
DISCLOSURE INFORMATIONThe authors had no financial conflicts of interest.
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Mathew I. B. Debenham PhD; Colin K. Franz MD, PhD; Michael J. Berger MD, PhD