Preliminary Evaluation of the Audio-Visual EMG (AVEMG) Method to Analyze the Interference Pattern

Quantitative analysis should be useful to all electrodiagnostic medical consultants (EMC). We tested a beta version of the audio-visual electromyography (AVEMG) method that quantifies the audio and visual characteristics of the interference pattern (IP) signal assessed by the EMC.

IP was recorded from multiple sites in 10 commonly tested upper and lower limb muscles. For each 200 ms epoch, AVEMG measured its Amplitude, Fullness and Pitch. Pitch reflects the sound characteristics, e.g., dull, sharp. The firing rate of motor units and discreteness of the pattern was also assessed. Reference (RVs) values were defined for Amplitude and Pitch based on Fullness of the pattern using recordings from 10 to 14 normal subjects. Normal and abnormal muscles were tested in 36 patients referred to the laboratory (139 muscles). The concordance between subjective assessment and AVEMG was assessed by a χ ² test.

AVEMG successfully rejected most epochs with noise, interference, spontaneous activity, insertional activity and needle artifacts. RVs differed among muscles. As example, the first dorsal interosseous and triceps had the highest Amplitude in upper limb muscles. AVEMG was abnormal in 80% of studies considered abnormal by subjective assessment. The association between subjective assessment and AVEMG was statistically significant (χ ² (1, N = 139) = 59, p < 0.0001).

AVEMG provides real time quantitation in the background and does not interfere with workflow or add examination time or complexity to the routine needle EMG examination. It will be of interest to further assess its value by refining RVs and performing multicenter studies with operators having different skill levels.