Identification and classification of involuntary leg muscle contractions in electromyographic records from individuals with spinal cord injury

Involuntary muscle contractions (spasms) are common after human spinal cord injury (SCI). Our aim was to compare how well two raters independently identified and classified different types of spasms in the same electromyographic records (EMG) using predefined rules. Muscle spasms were identified by the presence, timing and pattern of EMG recorded from paralyzed leg muscles of four subjects with chronic cervical SCI. Spasms were classified as one of five types: unit, tonic, clonus, myoclonus, mixed. In 48 h of data, both raters marked the same spasms most of the time. More variability in the total spasm count arose from differences between muscles (84%; within subjects) than differences between subjects (6.5%) or raters (2.6%). Agreement on spasm classification was high (89%). Differences in spasm count, and classification largely occurred when EMG was marked as a single spasm by one rater but split into multiple spasms by the other rater. EMG provides objective measurements of spasm number and type in contrast to the self-reported spasm counts that are often used to make clinical decisions about spasm management. Data on inter-rater agreement and discrepancies on muscle spasm analysis can both drive the design and evaluation of software to automate spasm identification and classification.