Quantitative sonographic assessment of myotonia.

INTRODUCTION: This study explores ultrasound imaging for qualitative and quantitative assessment of myotonia.

METHODS: Sixteen patients with myotonia and 16 controls underwent sonographic evaluation of the thenar eminence muscles to assess the relaxation time after muscle percussion.

RESULTS: The mean time for complete muscle relaxation in patients with myotonia was longer than that of controls. A cutoff of > 0.9 s for myotonia detection had a sensitivity of 88% and a specificity of 100%. The interrater reliability was moderate for qualitative assessment but was high for quantitative assessment. The relaxation time did not correlate with the number of trinucleotide repeats in patients with myotonic dystrophy.

DISCUSSION: Sonographic evaluation for the presence of myotonia is feasible, sensitive, and specific but does not correlate with disease severity in myotonic dystrophy. Muscle Nerve 57: 146-149, 2018.