Superiority of sonographic evaluation of contracted versus relaxed muscle thickness in motor neuron diseases

Objective: To compare the correlations of relaxed and contracted limb muscle thickness with clinical scales in patients with amyotrophic lateral sclerosis (ALS) and spinal muscular atrophy (SMA). Methods: Patients with ALS and SMA were prospectively recruited from December 2018 to November 2019. All patients underwent clinical assessment and sonographic muscle thickness measurement of eight relaxed muscles (biceps brachii, abductor pollicis brevis (APB), first dorsal interosseous, abductor digiti minimi, quadriceps, tibialis anterior, extensor digitorum brevis, and abductor hallucis brevis), and four contracted muscles (biceps brachii, APB, quadriceps, and tibialis anterior). Results: 91 patients with ALS and 31 patients with SMA were recruited. Contracted muscle thickness compared to relaxed muscle showed higher reliability and similar or better correlations with muscle strength and clinical scales, especially in ALS patients with hyperreflexia. Strong to very strong correlations with clinical scales were observed with multivariate analysis of relaxed and contracted muscle thickness (0.64–0.87). Conclusions: Sonographic evaluation of contracted muscle thickness is an objective measure that correlates with disease burden. It is feasible, quick, valid and reliable, and may be superior to evaluation of relaxed muscles. Significance: Sonographic evaluation of contracted muscle thickness is superior to evaluation of relaxed muscles.