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.

Keywords: Hand held dynamometry; Manual muscle testing; Motor neuron disease; Spinal muscular atrophy; TQNE.

Figures

Fig. 1

A comparison between Medical Research Council strength grading and quantitative strength measurements for biceps femoris. Reprinted with permission from van der Ploeg et al. [15]. Copyright 1984 Journal of Neurology

Fig. 2

Quantitative muscle strength measured using hand-held dynamometry as a function of serum concentration of tirasemtiv from a meta-analyis of 3 small, phase II studies. The trend for increased strength as a function of serum concentration is statistically significant (p < 0.002). Reprinted with permission from Shefner et al. [34]. Copyright 2013 Amyotrophic lateral sclerosis & frontotemporal degeneration

Fig. 3

Side-to-side correlations between 3 muscle groups (elbow flexion, shoulder flexion, ankle dorsiflexion) in both the ceftriaxone and dexpramipexole clinical trials. Reprinted with permission from Shefner et al. [37]. Copyright 2004 Neurology