Needle EMG of the tongue: motor unit action potential versus peak ratio analysis in limb and bulbar onset amyotrophic lateral sclerosis

Abstract

OBJECTIVES to find out if conventional and automatic needle EMG of the tongue can be helpful in the diagnosis and differentiation of limb and bulbar onset amyotrophic lateral sclerosis. METHODS Motor unit action potential (MUAP) analysis and peak ratio interference pattern analysis were performed in the right genioglossus muscle of 30 healthy subjects aged 30–81 years, 10 patients aged 49–73 years with limb onset amyotrophic lateral sclerosis, and eight patients aged 52–75 years with bulbar onset amyotrophic lateral sclerosis. Electrical activity was sampled via standard concentric needle electrodes with a commercially available EMG recorder. RESULTS Normal mean (2SD) MUAP duration was 6.6 (1.5) ms. Normal mean (2SD) MUAP amplitude was 224 (97.4) μV. Normal mean (2SD) peak ratio (PR), turns/second (T/s), amplitude/turn (A/T), and time intervals (TI1, TI2, TI3) were 1.68 (0.56), 732 (303.9), 446 (180.3) μV, 2.62 (0.34), 2.31 (0.14), and 1.01 (0.50) respectively. Mean MUAP duration and amplitude were significantly increased in limb onset (P=0.0001 and P=0.013) and bulbar onset amyotrophic lateral sclerosis (P=0.0001 and P=0.017). Peak ratio indices stayed unchanged in limb onset amyotrophic lateral sclerosis but were significantly decreased (PR, T/s, A/T, TI1, and TI2) or increased (TI3) in bulbar onset disease. The sensitivity of the MUAP analysis was 70% in limb and 75% in bulbar onset amyotrophic lateral sclerosis. The sensitivity of the peak ratio interference pattern analysis was 20% in limb and 100% in bulbar onset amyotrophic lateral sclerosis. Subclinical involvement of the tongue was found in 20% of the patients with limb onset amyotrophic lateral sclerosis and could be more accurately assessed with MUAP analysis than with automatic EMG. CONCLUSIONS both conventional and automatic needle EMG of the tongue are valuable electrophysiological devices to assess the clinical and subclinical involvement of the tongue in patients with limb and bulbar onset amyotrophic lateral sclerosis.