Journal CME, April 2022: Extensor digitorum brevis bulk and associations with fibular motor nerve conduction amplitude-Extensor digitorum brevis bulk

Extensor digitorum brevis bulk - article.pdf

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This study investigates the relationship between extensor digitorum brevis (EDB) muscle bulk and fibular motor nerve compound motor action potential (CMAP) amplitude among 52 adult participants. Previous research established that a CMAP amplitude of 4.0 mV or higher is crucial for ankle proprioception and reducing fall risk. The aim was to determine if EDB muscle bulk could serve as a reliable clinical surrogate marker for CMAP amplitude.<br /><br />The study included a prospective inter-rater reliability assessment and correlated EDB muscle bulk with fibular CMAP amplitudes. The inter-rater reliability for assessing EDB bulk was moderate (kappa: 0.65). The findings demonstrated a mean CMAP value of 5.9 mV for normal bulk, 3.4 mV for diminished bulk, and 0.6 mV for atrophied bulk. Analyses revealed EDB muscle bulk, distal symmetric polyneuropathy (DSP), and lumbar radiculopathy were all significantly associated with CMAP amplitude. EDB atrophy was a highly specific indicator (100% specificity) of a CMAP amplitude below 4.0 mV. Sensitivity for detecting abnormal CMAP (below 4.0 mV) was 0.86, with a specificity of 0.71.<br /><br />The study concludes that evaluating EDB muscle bulk is a simple and effective method for assessing fibular CMAP amplitude and identifying potential neuromuscular impairments. This clinical assessment can provide valuable insights into fall risk, especially in individuals with signs of DSP or lumbar radiculopathy. Despite the limitations of inter-rater reliability among trainees and potential bias in blinding during CMAP measurement, the findings suggest a practical approach for early detection and intervention strategies to prevent falls. Further research is recommended to directly link EDB muscle bulk evaluation with fall risk predictions.

Keywords

extensor digitorum brevis

EDB muscle bulk

fibular motor nerve

CMAP amplitude

ankle proprioception

fall risk

distal symmetric polyneuropathy

lumbar radiculopathy

neuromuscular impairments

clinical assessment