[Manual and quantitative muscle testing in neuromuscular disorders. How to assess the consistency of strength measurements in clinical trials?]

Masseter muscle volume as a disease marker in adult-onset myotonic dystrophy type 1

The advent of clinical trials in myotonic dystrophy type 1 (DM1) necessitates the identification of reliable outcome measures to quantify different disease manifestations using minimal number of assessments. In this study, clinical correlations of mean masseter volume (mMV) were explored to evaluate its potential as a marker of muscle involvement in adult-onset DM1 patients. We utilised data from a preceding study, pertaining to 39 DM1 patients and 20 age-matched control participants. In this study participants had undergone MRI of the brain, completed various clinical outcome measures and had CTG repeats measured by small-pool PCR. Manual segmentation of masseter muscles was performed by a single rater to estimate mMV. The masseter muscle was atrophied in DM1 patients when compared to controls (p<0.001). Significant correlations were found between mMV and estimated progenitor allele length (p = 0.001), modal allele length (p = 0.003), disease duration (p = 0.009) and and the Muscle Impairment Rating Scale (p = 0.008). After correction for lean body mass, mMV was also inversely correlated with self-reported myotonia (p = 0.014). This study demonstrates that changes in mMV are sensitive in reflecting the underlying disease process. Quantitative MRI methods demonstrate that data concerning both central and peripheral disease could be acquired from MR brain imaging studies in DM1 patients.

Assessment of muscle strength in para-athletes: A systematic review of observational studies

Accurate and reliable evaluation of muscle strength in para-athletes is essential for monitoring the effectiveness of strength training and/or rehabilitation programmes, and sport classification. Our aim is to synthesise evidence related to assessing muscle strength in para-athletes. Four databases were searched from January 1990 to July 2021 for observational studies focusing on strength assessment. Independent screening, data extraction, and quality assessment were performed in duplicate. A total of 1764 potential studies were identified. Thirty met the inclusion criteria and were included in the review. The mean age of participants was 30.7 years (standard deviation [SD]: 2.4). The majority were men (88%) participating in wheelchair sports, including basketball, rugby, and tennis (23/30: 76%). Overall quality varied, with more than half of the studies failing to identify strategies for dealing with confounding variables. Despite manual muscle testing being a standard component of para-sport classification systems, evidence examining strength characteristics in para-athletes is derived primarily from isometric and isokinetic testing. In studies that included comparative strength data, findings were mixed. Some studies found strength values were similar to or lower than able-bodied athletic controls. However, an important observation was that others reported higher shoulder strength in para-athletes taking part in wheelchair sports than both able-bodied and disabled non-athletes. Studies need to develop accessible, standardised strength testing methods that account for training influence and establish normative strength values in para-athletes. There is also a need for additional studies that include female para-athletes and para-athletes with greater functional impairments.

Development of new outcome measures for adult SMA type III and IV: a multimodal longitudinal study

OBJECTIVE

The aim of this study was the comprehensive characterisation of longitudinal clinical, electrophysiological and neuroimaging measures in type III and IV adult spinal muscular atrophy (SMA) with a view to propose objective monitoring markers for future clinical trials.

METHODS

Fourteen type III or IV SMA patients underwent standardised assessments including muscle strength testing, functional evaluation (SMAFRS and MFM), MUNIX (abductor pollicis brevis, APB; abductor digiti minimi, ADM; deltoid; tibialis anterior, TA; trapezius) and quantitative cervical spinal cord MRI to appraise segmental grey and white matter atrophy. Patients underwent a follow-up assessment with the same protocol 24 months later. Longitudinal comparisons were conducted using the Wilcoxon-test for matched data. Responsiveness was estimated using standardized response means (SRM) and a composite score was generated based on the three most significant variables.

RESULTS

Significant functional decline was observed based on SMAFRS (p = 0.019), pinch and knee flexion strength (p = 0.030 and 0.027), MUNIX and MUSIX value in the ADM (p = 0.0006 and 0.043) and in TA muscle (p = 0.025). No significant differences were observed based on cervical MRI measures. A significant reduction was detected in the composite score (p = 0.0005, SRM = -1.52), which was the most responsive variable and required a smaller number of patients than single variables in the estimation of sample size for clinical trials.

CONCLUSIONS

Quantitative strength testing, SMAFRS and MUNIX readily capture disease progression in adult SMA patients. Composite multimodal scores increase predictive value and may reduce sample size requirements in clinical trials.

Routine monitoring of isometric knee extension strength in patients with muscle impairments using a new portable device: cross-validation against a standard isokinetic dynamometer

OBJECTIVE

Muscle strength is a critical clinical hallmark in both health and disease. The current study introduces a novel portable device prototype (MyoQuad) for assessing and monitoring maximal voluntary isometric knee extension torque (MVIT).

APPROACH

Fifty-six patients with inclusion body myositis were studied. Knee extension weakness is a key feature in this inflammatory muscle disease. Cross-validation with an isokinetic dynamometer (Biodex System 3 Pro) was performed. Between-day reproducibility and ability to monitor changes in muscle strength over time compared to the gold standard method as a reference, were also investigated.

MAIN RESULTS

The measurement was feasible even in the weakest patients. Agreement between methods was excellent (standard error of measurement (SEM) was 3.8 Nm and intra-class correlation coefficient (ICC) was 0.973). Least significant difference (LSD) was 4.9 and 5.3 Nm for the MyoQuad and the Biodex, respectively Measurements using the MyoQuad exhibited excellent between-day reproducibility (SEM was 2.4 Nm and ICC was 0.989 versus 2.6 Nm and 0.988 using the Biodex). Changes in MVIT at 6 and 12 months were similar between methods (timepoint  ×  method interaction was not significant; all p   >  0.19); strength changes classified according to LSD at 6 and 12 months were consistent between methods (>70% consistent classification)).

SIGNIFICANCE

The measurement of MVIT using the MyoQuad offers a cost-effective, portable and immediate alternative for the routine measurement of maximal voluntary isometric strength of the quadriceps. The MyoQuad offers a comfort and stability that cannot be provided by standard hand-held dynamometers. These results support quantitative muscle strength assessment using fixed yet flexible dynamometry within clinical routine and multicenter trials.

Biomarkers of Spinal and Bulbar Muscle Atrophy (SBMA): A Comprehensive Review

Spinal and bulbar muscular atrophy (SBMA), also known as Kennedy's disease, is a rare, X-linked, late onset neuromuscular disorder. The disease is caused by a CAG trinucleotide repeat expansion in the first exon of the androgen receptor gene. It is characterized by slowly progressive lower motor neurons degeneration, primary myopathy and widespread multisystem involvement. Respiratory involvement is rare, and the condition is associated with a normal life expectancy. Despite a plethora of therapeutic studies in mouse models, no effective disease-modifying therapy has been licensed for clinical use to date. The development of sensitive monitoring markers for the particularly slowly progressing pathology of SBMA is urgently required to aid future clinical trials. A small number of outcome measures have been proposed recently, including promising biochemical markers, which show correlation with clinical disability and disease-stage and progression. Nevertheless, a paucity of SBMA-specific biomarker studies persists, delaying the development of monitoring markers for pharmaceutical trials. Collaborative efforts through international consortia and multicenter registries are likely to contribute to the characterization of the natural history of the condition, the establishment of disease-specific biomarker panels and ultimately contribute to the development of disease-modifying drugs.

Valores normativos de la fuerza de puño en la población española en edad laboral. Influencia de las variables antropométricas de la mano y el antebrazo

Objetivos: Determinar si en los individuos adultos sanos existe una apertura óptima del dinamómetro para conseguir la máxima fuerza de puño y si esta se relaciona con los valores de los parámetros antropométricos del antebrazo y la mano. Saber si a través de las medidas antropométricas del antebrazo y la mano es posible predecir la fuerza de puño que puede desarrollar un persona.

Métodos: 99 hombres y 103 mujeres (20-60 años). Cada mano se testó 10 veces, utilizando 5 aperturas del dinamómetro TKK. Las medidas antropométricas tomadas fueron ancho de la mano abierta, longitud del segundo, el tercer y el cuarto dedos, anchura de la palma, longitud de la palma, longitud de la mano, longitud del antebrazo, perímetro del antebrazo y grosor de la eminencia tenar.

Resultados: Con solo 2 aperturas (5,5-6 cm en varones, 5-5,5 cm en mujeres) se consiguió la máxima fuerza de puño en más del 60% de los individuos. El tamaño de la mano y el antebrazo influyó en la posición de apertura óptima en las mujeres, no en los varones. Los parámetros antropométricos que mejor definieron la fuerza fueron diferentes según el sexo y el lado, pero en ningún caso se logró que el valor de R2 superase el 0,50.

Conclusiones: La máxima fuerza de puño se consigue utilizando las posiciones medias del dinamómetro, siendo en mujeres la apertura menor que en varones. Empleando exclusivamente los parámetros antropométricos de la mano y el antebrazo no se consigue un valor predictivo útil, como el obtenido por otros autores con otras medidas antropométricas.

Lower limb muscle impairment in myotonic dystrophy type 1: the need for better guidelines

In myotonic dystrophy type 1 (DM1), leg muscle weakness is a major impairment. There are challenges to obtaining a clear portrait of muscle strength impairment. A systematic literature review was conducted on lower limb strength impairment in late-onset and adult phenotypes to document variables which affect strength measurement. Thirty-two articles were reviewed using the COSMIN guidelines. Only a third of the studies described a reproducible protocol. Only 2 muscle groups have documented reliability for quantitative muscle testing and only 1 total score for manual muscle testing. Variables affecting muscle strength impairment are not described in most studies. This review illustrates the variability in muscle strength assessment in relation to DM1 characteristics and the questionable validity of the results with regard to undocumented methodological properties. There is therefore a clear need to adopt a consensus on the use of a standardized muscle strength assessment protocol.

Muscle strength in myasthenia gravis

OBJECTIVE

Myasthenia gravis (MG) is characterized by fatigue and fluctuating muscle weakness as a result of impaired neuromuscular transmission (NMT). Although MG is a prototypic fatiguing disorder, little is known about how the condition affects fixed weakness, and if present, whether weakness is related to disease duration or gender. The aim of this study was to quantify the strength of patients with MG and investigate whether it is related to disease duration.

METHODS

Eight muscle groups were tested by manual muscle testing and with a hand-held dynamometer in 38 patients with generalized MG and 37 healthy age- and gender-matched controls. The disease duration was recorded and compared with strength measures.

RESULTS

On average, muscle strength was decreased by 28% compared with controls (P<0.01). Repeated strength measures in individual patients did not differ, suggesting that the muscle force reported was not subject to fatigue, but reflected fixed weakness. The male patients showed a greater reduction in muscle force in all eight muscle groups than women with MG (60% vs 77% of normal, P<0.05). In both men and women with MG, strength in shoulder abductors was most affected (51% vs 62% of normal). Muscle strength and disease duration were not related.

CONCLUSIONS

These findings show that patients with generalized MG have (i) a significant generalized, fixed muscle weakness, (ii) that male patients with MG have a more severe muscle weakness than women, (iii) that proximal upper limb muscles are most affected, and (iv) that disease duration alone is not a predictor of loss of muscle strength.

Isokinetic testing in patients with neuromuscular diseases: a focused review

OBJECTIVE

This literature review aimed to study the use of isokinetic testing in patients with neuromuscular diseases (NMDs) and to identify directions for future research of isokinetic testing.

DESIGN

The MEDLINE (January 1, 1965, to July 1, 2010), Cumulative Index to Nursing and Allied Health (1980 to May 2010), and Cochrane Central Register of Controlled Trials (The Cochrane Library Issue 3, 2009) electronic databases were searched. The literature search was conducted using the keywords muscle assessment, muscle strength, evaluation, isokinetic, neuromuscular diseases, muscle fatigue, functional test, rehabilitation, and literature search. Relevant references cited in the selected articles were also considered, regardless of the year of publication.

RESULTS

The search strategy yielded 13 articles involving a variety of patients with known NMDs. All studies demonstrated that isokinetic dynamometry is appropriate and safe for ambulatory patients with NMDs. Isokinetic testing has proven to be reliable (intratest/intertest correlation coefficient ranged from 0.65 to 0.98), with the proximal muscles having the highest reliability, and sensitive to disease progression and to the effects of various therapeutic interventions. However, isokinetic testing has never gained wide acceptance, partly because of concerns about stabilizing the dynamometer and the subject during the test and of the lack of standardized protocols for isokinetic strength measurement.

CONCLUSIONS

Isokinetic testing is an important part of the comprehensive evaluation and rehabilitation of patients with NMD. Research has demonstrated its efficacy in providing clinically relevant information. When integrated with a complete history, physical examination, and functional evaluation, isokinetic testing and exercise can be a valuable tool for the clinician in the assessment, rehabilitation, and performance enhancement of patients with NMD. Such equipment, however, has several disadvantages, rendering it usually impractical in the clinical setting.

Development of a French Isometric Strength Normative Database for Adults Using Quantitative Muscle Testing

OBJECTIVE

To establish a normative database for isometric strength measured by quantitative muscle testing (QMT) for a French adult population.

DESIGN

Measurement of maximal voluntary isometric contraction.

SETTING

Four clinical centers involved in neuromuscular disorders.

PARTICIPANTS

A total of 315 healthy adults (147 men, 168 women) ages 20 to 80 years.

INTERVENTIONS

Not applicable.

MAIN OUTCOME MEASURE

Isometric torque values of 14 muscle functions (13 bilaterally and neck).

RESULTS

This study led to the development of a French isometric strength normative database for adults measured by QMT. For each muscle function, predictive regression models using age, sex, and weight are proposed. Some methodologic issues concerning strength measurement are discussed.

CONCLUSIONS

This database can be used to compute relative deficits in muscle strength for 27 muscle functions and also to estimate composite scores for follow-up of patients either during the natural history of their disease or during a therapeutic trial.