Long-term monitoring of stimulated lower leg skeletal muscle forces compared with voluntary contractions in myopathy patients – A five-year follow-up report on 5 adults

Objective: Long-term assessments of lower leg muscle forces in ambulant patients with distal myopathies. Methods and materials: Over a five-year period, we measured involuntary, nerve-stimulated, isometric torques of the ankle dorsiflexors in a group of ambulant patients with myopathies and compared results with voluntary Manual Muscle Tests (MMT). Results: From ten recruited patients, five could finish the five-year protocol. Twenty-seven force measurements sessions (one per year; 1,5 hours duration each) were performed. These patients exhibited low, stable torques or increased minimally (0.2 Newtonmeter, versus 0.1 Nm, ns; 0.7 vs. 1.0, ns; 3.4 vs. 3.5, ns; 0.2 vs. 0.1, ns; 0.8 vs. 1.5, P 0.0004 initial values vs. 5-year values, [norm: 3.9–5.7 Nm]). A 6th patient, eliciting low torque values (0.1 Nm) early passed away. Contraction times inversely correlated with MMT. MMT provided similar overall force abilities. Conclusions: Long-term monitoring of lower leg muscle forces in ambulant patients is limited by the patient's health status. In a small group of patients, stimulated lower leg forces did not worsen over many years relative to their diagnosed myopathies. Tracking involuntary forces, could be a useful monitoring providing phenotypic information, in addition to MMT. Future devices should be small and be simply self-applying, designed for subjects' domestic use and web-based data transfer. ClinicalTrials.gov NCT00735384.