Muscle velocity recovery cycles in neurogenic muscles

Abstract

Objective: To examine muscle membrane properties in neurogenic muscles using Muscle Velocity Recovery Cycles (MVRCs).

Methods: Forty-seven patients referred to Nerve Conduction Studies (NCS) and Electromyography (EMG) for peroneal nerve entrapment neuropathy were prospectively included. The patients were categorized as peroneal nerve entrapment neuropathy across knee (n = 22), L5-radiculapathy (n = 10), normal NCS/EMG (n = 9) and other disorders (n = 6) using NCS/EMG and neuroimaging results. Strength in anterior tibial muscle was measured by Medical Council Scale (MRC) and disease duration was recorded. In addition to conventional NCS/EMG, all subjects were examined with MVRCs in anterior tibial muscle. This provided parameters of muscle relative refractory period (MRRP) and early supernormality (ESN) and late supernormality (LSN). The results were compared with 29 age-matched healthy control subjects.

Results: MRRP was prolonged and ESN and LSN were reduced in neurogenic muscles. MRRP, ESN and LSN correlated to MRC and incidence of spontaneous activity but not to motor unit potential parameters or disease duration.

Conclusions: MVRC changes provide in vivo evidence of depolarization in intact human muscle fibres that could underlie reduced muscle excitability and hence weakness in neurogenic muscles.

Significance: MVRCs appear to be a useful technique for revealing disease mechanism in a broad range of neuromuscular diseases.

Keywords: EMG; Muscle membrane depolarization; Muscle strength; Muscle velocity recovery cycles (MVRCs); NCS; Peroneal nerve neuropathy; Radiculopathy.