Submitted by: Nandita Keole, MD
Edited by: Pritikanta Paul, MD
Citation: Alazzam AM, Goldsmith JA, Khalil RE, et al. Denervation impacts muscle quality and knee bone mineral density after spinal cord injury. Spinal Cord. 2023 Apr;61(4):276-284. doi: 10.1038/s41393-023-00885-3. Epub 2023 Mar 10. PMID: 36899099.
Summary: Conducted at a single center, this cross-sectional study aimed to compare muscle size, body composition, bone mineral density (BMD), and metabolic profiles between two groups: individuals with spinal cord injury (SCI) characterized by denervation lower motor neuron (LMN) and those with innervation upper motor neuron (UMN).
Body composition, BMD, muscle size, and metabolic parameters were collected in 16 persons with chronic SCI (n = 8 denervated, n = 8 innervated) using dual-energy x-ray absorptiometry (DXA), magnetic resonance imaging (MRI), and fasting blood samples. Basal metabolic rate (BMR) was measured by indirect calorimetry. On assessment with the American Spinal Injury Association Impairment Scale (AIS) [Grade A is complete loss of motor and sensory function below level of injury and Grade E is normal motor and sensory function], seven participants in the denervated group were A and one was C. In the UMN injury group three participants were AIS A, two AIS B, and three AIS C. Percent differences of the whole thigh muscle cross-sectional area (CSA; 38%), knee extensor CSA (49%), vasti CSA (49%), and rectus femoris CSA (61%) were smaller in the denervated group (p < 0.05). Leg lean mass was also lower (28%) in the denervated group (p < 0.05). Whole muscle intramuscular fat (IMF%; 15.5%), knee extensor IMF% (22%), and % fat mass (10.9%) were significantly greater in the denervated group (p < 0.05). Knee distal femur and proximal tibia BMD were lower in the denervated group, 18–22% and 17–23%; p < 0.05. Certain indices of metabolic profile were more favorable in the denervated group though were not significant.
SCI results in skeletal muscle atrophy and dramatic changes in body composition. LMN injury results in denervation of the lower extremity muscles which exacerbates atrophy. Denervated participants exhibited lower leg lean mass and muscle CSA, greater muscle IMF, and reduced knee BMD compared to innervated (UMN injury) participants. Future research is needed to explore therapeutic treatments for the denervated muscles after SCI.
Comments: This highlights musculoskeletal changes in a lesser reviewed subpopulation in SCI patients. Level of lesion alone does not help differentiate UMN and LMN patients. This article highlights some gaps in knowledge for the LMN SCI patients and will influence plan of care and education with regards to therapy and activity. It would be interesting to see if LMN patients may derive more benefits from robotic assisted exoskeletons.
