Abstract
Objectives We prospectively assessed the diagnostic utility of quantitative muscle ultrasound to distinguish amyotrophic lateral sclerosis (ALS) patients from neuromuscular mimics. Additionally, we explored the association between ultrasound parameters and clinical markers of disease severity.
Methods 46 patients suspected of ALS were studied using ultrasound of 17 different muscle groups. Muscle fasciculations and quantitative muscle echo-intensity were recorded. Muscle specific echo-intensity reference values were generated from 39 healthy controls, with hyperechoic muscles defined as a Z score >1.5 SD. The diagnostic utility of these metrics and their association with disease severity was determined.
Results 34 patients met the diagnosis of ALS over the follow up period. 12 patients were diagnosed with other neuromuscular disorders. Longer ALS disease duration was associated with more hyperechoic muscles (r=0.44 p=0.003) and less fasciculating muscles (r=0.35 p<0.001). ALS subjects had significantly more fasciculating muscles when compared to mimic subjects (mean 7.9±3.9 vs 1.9±2.8 p<0.01). By contrast, the number of hyperechoic muscles was not significantly different between groups (mean 2.0±0.3 vs 3.1±0.9 p=0.167). In the diagnosis of ALS ≥ 5 fasciculating muscles was 82% sensitive and 87.5% specific (AUC 0.88) while a total fasciculation count of ≥7 was 82% sensitive and 75% specific (AUC = 0.86). The ratio of fasciculating muscles to hyperechoic muscles was calculated. A ratio of ≥ 1.5 was 87% sensitive and 89% specific (AUC 0.94) for ALS.
Conclusions The ratio of fasciculating muscles to hyperechoic muscles on ultrasound is highly accurate for the diagnosis of ALS.
