"Fascicular twitch" on muscle ultrasonography in neuromuscular disorders: quantitative video-image analysis.

OBJECTIVE

In contrast to needle electromyography, the diagnostic performance of muscle ultrasound (MUS) for differentiating neurogenic from myopathic disorders remains unclear. We examined the clinical utility of "fascicular twitch," a visible movement of muscle bundles during isometric contraction, and evaluated its ability to differentiate neurogenic from myopathic changes.

METHODS

We quantified fascicular twitches on MUS during isometric contraction as normalized twitch pixels (nTP) using an original image analysis method based on background subtraction. We analyzed echogenicity and nTP values in the biceps brachii muscle of 89 patients with neuromuscular disorders and 42 controls.

RESULTS

The neurogenic group demonstrated substantially higher nTP values than the myopathic group and controls, achieving a sensitivity of 90.5% and specificity of 88.1% at an nTP cutoff of 0.04. Although echogenicity distinguished patients with neuromuscular disorders from controls, it failed to discriminate between the neurogenic and myopathic groups.

CONCLUSIONS

Quantification of fascicular twitch via nTP effectively differentiates neurogenic from myopathic disorders, thereby demonstrating that MUS is a valuable, noninvasive diagnostic method for assessing neuromuscular diseases.

SIGNIFICANCE: This study introduces fascicular twitch quantification as a novel ultrasound biomarker that uniquely discriminates neurogenic from myopathic pathology, offering a high‑performance, noninvasive approach to neuromuscular diagnosis.