Quantitative myotonia assessment: an experimental protocol

Abstract

Severe clinical myotonia can be physically disabling and socially impairing but as yet there is no standardized treatment regimen. The aim of our study is to present a protocol to measure myotonia using quantitative muscle assessment measures. The proposed protocol addresses two main issues. Muscle strength is assessed in 8 muscles on the right and on the left using a myometer (QMA, quantitative muscle assessment) and by testing strength manually using the 5-point MRC scale (5 = normal) in 15 muscles on the right and on the left. Grip myotonia is assessed by: (a) measuring 1/2 and 3/4 relaxation times (RT) after maximum voluntary contraction (MVC) using QMA apparatus; (b) functional tests (time to open a fist 10 times, time to open and squeeze the eyes 10 times, time to climb 10 steps starting from a seated position, time to protrude the tongue 10 times, time to step onto a chair 10 times; (c) subjective measures of the severity of myotonia using an arbitrary 4-point scale (0 = absent, 4 = severe); and (d) electromyography (EMG) relaxation times after MVC. Although QMA seems to be a reliable tool to measure myotonia, there are still a number of unsolved issues. Further studies are needed to ensure the ability of QMA to quantify myotonia and to guarantee the reliability of the results for clinical research purposes.

Trunk sway analysis to quantify the warm-up phenomenon in myotonia congenita patients

“…In our study, this warm-up effect was most clearly present during tandem walking. Others noted an improvement in timed performance during stair climbing and the “get-up-and-go” test,6 7 16 and this effect was also observed in the present study, along with improvements in trunk stability for these tasks.…”

“…These tests were chosen based on our prior experience in patients with different balance disorders,12 – 14 as well as on clinical experience in RMC where the “timed get up and go‘ test and stair climbing have been used previously for myotonia assessment 6 7 16. Moreover, getting-up from and then walking around a chair was recently suggested as a possible functional test 8…”

“…These tests are very sensitive measures of myotonia, but do not reflect the patient’s functional capacities. On the other hand, it has proved difficult to score the presence and severity of myotonia based on clinical grounds alone 6. Explanations include the inter- and intraindividual variability in patients, but also the inter-rater variability.…”

A quantitative measure of handgrip myotonia in non‐dystrophic myotonia

“…Patients with potassium‐aggravated myotonia have delayed exercise‐induced myotonia, which is provoked by potassium, without changes in force 15. More recently, a commercially available quantitative measure of handgrip myotonia, quantitative myotonia assessment (QMA), has been used to calculate peak force and relaxation times after forced handgrips in patients with myotonic dystrophy type 1 (DM1) 16–20. This technique was subsequently used successfully to show a reduction in 90% to 5% relaxation time after treatment with mexiletine in a randomized, placebo‐controlled, cross‐over study in DM1.…”

Relationships between grip strength, myotonia, and CTG expansion in myotonic dystrophy type 1

“…Myotonia and muscle weakness are two main primary neuromuscular features in patients suffering from myotonic dystrophy type 1 (DM1). Both myotonia and muscle weakness are generally evidenced during maximal grip contractions and have been used as hallmarks of disease severity. DM1 is caused by expansion of a CTG trinucleotide repeat in the noncoding region of the DMPK gene.…”