Quantitative myotonia assessment: an experimental protocol

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

In myotonic dystrophy type 1, several studies have suggested causal relationships between CTG repeat length and the severity of symptoms, such as weakness or myotonia. We aimed to explore these relationships in a large population of 144 DM1 patients. All patients underwent clinical and functional assessments using a standardized test for grip strength and myotonia assessment. Myotonia was assessed using a fully automatic software based on mathematical modeling of relaxation force curve. CTG repeat length was statistically correlated with both myotonia and grip strength, which are two major primary neuromuscular symptoms of DM1 patients. However, these relationships are not clinically meaningful and not predictive at the individual level.

Toward a more personalized motor function rehabilitation in Myotonic dystrophy type 1: The role of neuroplasticity

Myotonic dystrophy type 1 (DM1) is the most prevalent adult muscular dystrophy, often accompanied by impairments in attention, memory, visuospatial and executive functions. Given that DM1 is a multi-system disorder, it requires a multi-disciplinary approach, including effective rehabilitation programs, focusing on the central nervous system neuroplasticity, in order to develop patient-tailored rehabilitative procedures for motor function recovery. Herein, we performed a transcranial magnetic stimulation (TMS) study aimed at investigating central motor conduction time, sensory-motor plasticity, and cortical excitability in 7 genetically defined DM1 patients. As compared to healthy individuals, DM1 patients showed a delayed central motor conduction time and an abnormal sensory-motor plasticity, with no alteration of cortical excitability. These findings may be useful to define patient-tailored motor rehabilitative programs.

A quantitative measure of handgrip myotonia in non-dystrophic myotonia

INTRODUCTION

Non-dystrophic myotonia (NDM) is characterized by myotonia without muscle wasting. A standardized quantitative myotonia assessment (QMA) is important for clinical trials.

METHODS

Myotonia was assessed in 91 individuals enrolled in a natural history study using a commercially available computerized handgrip myometer and automated software. Average peak force and 90% to 5% relaxation times were compared with historical normal controls studied with identical methods.

RESULTS

Thirty subjects had chloride channel mutations, 31 had sodium channel mutations, 6 had DM2 mutations, and 24 had no identified mutation. Chloride channel mutations were associated with prolonged first handgrip relaxation times and warm-up on subsequent handgrips. Sodium channel mutations were associated with prolonged first handgrip relaxation times and paradoxical myotonia or warm-up, depending on underlying mutations. DM2 subjects had normal relaxation times but decreased peak force. Sample size estimates are provided for clinical trial planning.

CONCLUSION

QMA is an automated, non-invasive technique for evaluating myotonia in NDM.

Development of a disability scale for myotonic dystrophy type 1

OBJECTIVES

Myotonic dystrophy type 1 (DM1) is a multisystem disorder. Many tests in the literature have evaluated single aspects of DM1 patients, mainly focusing on muscular impairment, without an overall quantification of the different disease-specific neurological features. We developed and validated a new functional scale for DM1 patients based on neuromuscular impairment (NI) and disability.

MATERIALS AND METHODS

Thirty-three patients were tested in basal condition, 18 were re-evaluated after therapeutic intervention with mexiletine, and 13 at one year follow-up without treatment. The scale includes 21 ordinal items in four areas: neuropsychology, motricity, myotonia and daily life activities. We evaluated inter- and intra-observer reliability (intraclass correlation coefficient, ICC and Spearman correlations, respectively), internal consistency (Cronbach's alpha), external validity (Spearman correlations between each area and other clinical and objective measurements and scales), and sensitivity to clinical changes after treatment or at follow-up.

RESULTS

Our analysis provided good results for inter-observer agreement (ICC = 0.72-0.97), intra-observer reliability, and internal consistency for all areas (Cronbach's α > 0.73). Total score and single area subscores were significantly correlated to objective measurements, disease duration and multisystem involvement. Finally, the scale was sensitive to clinical changes disclosing a significant improvement after treatment in the items assessing myotonia, and also to disease progression showing a significant worsening in all areas but myotonia in untreated patients.

DISCUSSION

Our scale provides a new practical measure to evaluate NI and disability of DM1 patients. Further longitudinal studies are warranted to confirm its reliability in tracking disease progression and severity over a longer period of time.

Quantitative myotonia assessment using force relaxation curve modelling

The lack of a robust quantitative measure of myotonia has been underlined in previous studies. Recent publications have proposed methods to quantify myotonia based on the measurement of force relaxation times during maximal contractions. However, they present several drawbacks mainly due to unstable force, odd peaks or digital noise. A possible solution to this issue consists in fitting the force curve with a convenient regression model. The aim of this study was, therefore, to provide a regression model in order to fit the force relaxation time curve automatically and to provide a robust index for quantitative assessment of myotonia in clinical settings. Force curves were fitted by an asymmetric sigmoidal function. The inverse function was then used to compute various absolute and relative relaxation times automatically. These variables were calculated for 16 controls and 16 patients with myotonic dystrophy type 1 (DM1). All variables were significantly increased in DM1 patients compared to controls. For instance, the relaxation time between 40 and 60% of the initial contraction level was 18.2 (SD: 3.3) ms in controls and 40.1 (SD: 17.7) ms in DM1 patients. All relaxation variables were highly discriminant. Force curve modelling provides an objective and effective quantification of myotonia.

Assessment of precision and reproducibility of a new myograph

Background

The physiological characteristics of muscle activity and the assessment of muscle strength represent important diagnostic information. There are many devices that measure muscle force in humans, but some require voluntary contractions, which are difficult to assess in weak or unconscious patients who are unable to complete a full range of voluntary force assessment tasks. Other devices, which obtain standard muscle contractions by electric stimulations, do not have the technology required to induce and measure reproducible valid contractions at the optimum muscle length.

Methods

In our study we used a newly developed diagnostic device which measures accurately the reproducibility and time-changed-variability of the muscle force in an individual muscle. A total of 500 in-vivo measurements of supra-maximal isometric single twitch contractions were carried out on the musculus adductor pollicis of 5 test subjects over 10 sessions, with ten repetitions per session. The same protocol was performed on 405 test subjects with two repetitions each to determine a reference-interval on healthy subjects.

Results

Using our test setting, we found a high reproducibility of the muscle contractions of each test subject. The precision of the measurements performed with our device was 98.74%. Only two consecutive measurements are needed in order to assess a real, representative individual value of muscle force. The mean value of the force of contraction was 9.51 N and the 95% reference interval was 4.77–14.25 N.

Conclusion

The new myograph is a highly reliable measuring device with which the adductor pollicis can be investigated at the optimum length. It has the potential to become a reliable and valid tool for diagnostic in the clinical setting and for monitoring neuromuscular diseases.

In vivo myograph measurement of muscle contraction at optimal length

BACKGROUND

Current devices for measuring muscle contraction in vivo have limited accuracy in establishing and re-establishing the optimum muscle length. They are variable in the reproducibility to determine the muscle contraction at this length, and often do not maintain precise conditions during the examination. Consequently, for clinical testing only semi-quantitative methods have been used.

METHODS

We present a newly developed myograph, an accurate measuring device for muscle contraction, consisting of three elements. Firstly, an element for adjusting the axle of the device and the physiological axis of muscle contraction; secondly, an element to accurately position and reposition the extremity of the muscle; and thirdly, an element for the progressive pre-stretching and isometric locking of the target muscle. Thus it is possible to examine individual in vivo muscles in every pre-stretched, specified position, to maintain constant muscle-length conditions, and to accurately re-establish the conditions of the measurement process at later sessions.

RESULTS

In a sequence of experiments the force of contraction of the muscle at differing stretching lengths were recorded and the forces determined. The optimum muscle length for maximal force of contraction was established. In a following sequence of experiments with smaller graduations around this optimal stretching length an increasingly accurate optimum muscle length for maximal force of contraction was determined. This optimum length was also accurately re-established at later sessions.

CONCLUSION

We have introduced a new technical solution for valid, reproducible in vivo force measurements on every possible point of the stretching curve. Thus it should be possible to study the muscle contraction in vivo to the same level of accuracy as is achieved in tests with in vitro organ preparations.

Drug treatment for myotonia

BACKGROUND

Abnormal delayed relaxation of skeletal muscles, known as myotonia, can cause disability in myotonic disorders. Sodium channel blockers, tricyclic antidepressive drugs, benzodiazepines, calcium-antagonists, taurine and prednisone may be of use in reducing myotonia.

OBJECTIVES

To consider the evidence from randomised controlled trials on the efficacy and tolerability of drug treatment in patients with clinical myotonia due to a myotonic disorder.

SEARCH STRATEGY

We searched the Cochrane Neuromuscular Disease Group trials register (April 2004), MEDLINE (January 1966 to December 2003) and EMBASE (January 1980 to December 2003). Grey literature was handsearched and reference lists of identified studies and reviews were examined. Authors, disease experts and manufacturers of anti-myotonic drugs were contacted.

SELECTION CRITERIA

We considered all (quasi) randomised trials of participants with myotonia treated with any drug treatment versus no therapy, placebo or any other active drug treatment. The primary outcome measure was:reduced clinical myotonia using two categories: (1) no residual myotonia or improvement of myotonia or (2) No change or worsening of myotonia. Secondary outcome measures were:(1) clinical relaxation time; (2) electromyographic relaxation time; (3) stair test; (4) presence of percussion myotonia; and (5) proportion of adverse events.

DATA COLLECTION AND ANALYSIS

Two authors extracted the data independently onto standardised extraction forms and disagreements were resolved by discussion.

MAIN RESULTS

Nine randomised controlled trials were found comparing active drug treatment versus placebo or another active drug treatment in patients with myotonia due to a myotonic disorder. Included trials were double-blind or single-blind crossover studies involving a total of 137 patients of which 109 had myotonic dystrophy type 1 and 28 had myotonia congenita. The studies were of poor quality. Therefore, we were not able to analyse the results of all identified studies. Two small crossover studies without a washout period demonstrated a significant effect of imipramine and taurine in myotonic dystrophy. One small crossover study with a washout period demonstrated a significant effect of clomipramine in myotonic dystrophy. Meta-analysis was not possible.

AUTHORS' CONCLUSIONS

Due to insufficient good quality data and lack of randomised studies, it is impossible to determine whether drug treatment is safe and effective in the treatment of myotonia. Small single studies give an indication that clomipramine and imipramine have a short-term beneficial effect and that taurine has a long-term beneficial effect on myotonia. Larger, well-designed randomised controlled trials are needed to assess the efficacy and tolerability of drug treatment for myotonia.

Veränderung der Muskelkraft bei Patientinnen mit Anorexia nervosa während der stationären Behandlung - eine Pilotstudie

Zusammenfassung: Fragestellung: Die Veränderung der Muskelkraft bei Patientinnen mit Anorexia nervosa während der stationären Behandlung sollte durch exakte Messung bestimmt werden. Methode: Unter Verwendung einer etablierten Messvorrichtung inkl. des Softwareprogramms «Quantitative Muscle Assessment» wurden in den Wochen 1, 2, 3, 4, 6, 8 und 10 des stationären Aufenthaltes die Maximalkräfte in vier verschiedenen Übungen für jede Körperseite bei zehn Patientinnen bestimmt. Alle wiesen vor der stationären Aufnahme einen vergleichbaren Krankheitsverlauf mit reiner Nahrungsrestriktion ohne überdurchschnittliche sportliche Betätigung auf. Ergebnisse: Es ergaben sich Hinweise auf einen interindividuell zu beobachtenden mehrphasigen Verlauf der Kraftrestitution. Die aufgrund der einfachen Durchführung andernorts häufig angewandte Übung Handgrip zeigte im Gegensatz zu den anderen untersuchten Muskelgruppen keine einheitliche Entwicklung. Seitendifferenzen waren nicht zu beobachten. Schlussfolgerungen: Patientinnen mit Anorexia nervosa zeigen eine objektivierbare, interindividuell vergleichbare, mehrphasige Zunahme der Maximalkraft der untersuchten Muskelgruppen während der Gewichtsrestitution.