Aging Accelerates Degradation of Human Neuromuscular Junction Following Peripheral Nerve Injury

Clinical observations indicate differences between young versus older adults in outcomes of peripheral nerve injury (PNI). Here, we present an analysis of motor endplates (MEPs) from normal and denervated deltoid muscle biopsies from young adult (≤ 60 years) and older (> 60 years) patients.

Under an IRB-approved prospective cohort study protocol, 24 patients who underwent open surgery for either shoulder pathology or deltoid dysfunction secondary to axillary nerve injury, confirmed with electrodiagnostic studies, were evaluated. Deltoid muscle biopsies were procured at the time of surgery to assess MEP morphology and innervation status.

Analysis of the MEPs in denervated deltoid revealed no significant difference in the percentage of healthy (pretzel) versus unhealthy (intermediate/plaque) morphology between the young and older groups. However, there was a large difference between young versus old denervated deltoids in the percent of innervated MEPs. In young denervated muscle, an average of 48.61% (±12.40%) MEPs were innervated, while in older muscle samples an average of 24.78% (±5.83%) MEPs were innervated. Additionally, the older group had a faster initial rate of MEP nerve signal loss compared to the young group.

Our study shows that age does affect the MEP response to injury. This effect is most significant in MEP innervation, with rapid loss of visible innervated terminals in the older group. Surprisingly, there was no significant difference in MEP morphology in the older patients, suggesting that early surgical intervention may still offer significant recovery potential.