Strength Testing in Motor Neuron Diseases

Abstract

Loss of muscle strength is a cardinal feature of all motor neuron diseases. Functional loss over time, including respiratory dysfunction, inability to ambulate, loss of ability to perform activities of daily living, and others are due, in large part, to decline in strength. Thus, the accurate measurement of limb muscle strength is essential in therapeutic trials to best understand the impact of therapy on vital function. While qualitative strength measurements show declines over time, the lack of reproducibility and linearity of measurement make qualitative techniques inadequate. A variety of quantitative measures have been developed; all have both positive attributes and limitations. However, with careful training and reliability testing, quantitative measures have proven to be reliable and sensitive indicators of both disease progression and the impact of experimental therapy. Quantitative strength measurements have demonstrated potentially important therapeutic effects in both amyotrophic lateral sclerosis and spinobulbar muscular atrophy, and have been shown feasible in children with spinal muscular atrophy. The spectrum of both qualitative and quantitative strength measurements are reviewed and their utility examined in this review.

Neurologic examination and instrument‐based measurements in the evaluation of ulnar neuropathy at the elbow

“…Similar to sensory testing, we also found clinical assessment of muscle bulk to be more sensitive and specific than US measurement of FDI muscle CSA. By contrast, we confirmed previous findings for amyotrophic lateral sclerosis, 12 spinal cord injury, 13 and ulnar nerve lesions 5,14,15 of the higher sensitivity of dynamometry as compared to manual muscle strength testing, although differences in our patients were not large (86% vs. 82%; Table 1). The main problem of MRC testing is its nonlinearity.…”

An Appraisal of Novel Biomarkers for Evaluating and Monitoring Neurologic Diseases: Editorial Introduction

“…However, quantitative methods that are reliable across study centers and evaluators have not been routinely employed. Recently, different methods of assessing strength have been implemented in clinical trials of ALS and spinal muscular atrophy with very encouraging results [17]. Similarly, while functional rating scales are commonly used as outcome measures in diseases as diverse as stroke, MS, AD, ALS, and Parkinson's disease, recent modifications have improved the metric qualities of these measures, and allowed for use in the home [18].…”

Portable fixed dynamometry to quantify ankle dorsiflexion force

“…The MMT grading system was adjusted from the commonly used 6‐point Medical Research Council (MRC) scale to a 10‐point scale . This was done so that an ordinal scale with slightly improved sensitivity could be used to assess muscle function . MMT followed the guidelines of IMACS Form 04: Manual Muscle Testing Procedures…”

“…MMT is a common technique to assess muscle strength . It can be quickly executed and costs nothing, but it has significant drawbacks, including: (1) poor interrater reliability; (2) poor sensitivity, particularly for mild to moderate weakness; and (3) it is based on an ordinal scale. Dynamometers are an attractive alternative to MMT because ―they have high accuracy, and they sensitively and objectively quantify strength on a continuous scale .…”