Isometric skeletal muscle force measurement in primary myopathies.

Abstract

In myopathy patients, it is useful to measure skeletal muscle forces. Conventional methods require voluntary muscle activation, which can be unreliable. We evaluated a device for nonvoluntary force assessment. We tested 8 patients (unknown myopathy n = 2, inflammatory myopathy, facioscapulohumeral muscular dystrophy, mitochondrial myopathy, dysferlinopathy, multi-minicore disease, Becker-Kiener muscular dystrophy, n = 1 each). Isometric twitch torques of ankle dorsiflexors were measured after fibular nerve stimulation. Six patients had decreased torques vs. 8 controls (men: median Newton-meter 1.6 vs. 5.7, women: 0.2 vs. 3.9, both P < 0.0001). Values correlated with Manual Muscle Test results (r = 0.73; r(2) = 0.53; P < 0.0001). In weak dorsiflexors, torque could be measured despite lower signal-to-noise ratios. In 2 patients with hypertrophy, we measured increased torques. Nonvoluntary muscle force assessment can be used in patients with myopathies, and values correlate with voluntary forces determined by traditional methods. Muscle Nerve 53: 913-917, 2016.