Excessive muscular fatigue in patients with spastic paraparesis

Abstract

We used intermittent tetanic contractions and 31P magnetic resonance spectroscopy to investigate human tibialis anterior muscle metabolism and fatigability in a group of patients with spastic paraparesis and in normal controls. During intermittent tetanic stimulation, the decline in tension was significantly greater in patients than in controls, and the half-relaxation time of the tetanus was more prolonged. Moreover, the decline in phosphocreatine and intracellular pH was significantly greater in patients than in controls. These observations suggest that biochemical changes in the muscles of patients with upper motor neuron lesions may contribute to their excessive fatigability.

Evidence of an abnormal intramuscular component of fatigue in multiple sclerosis

“…Subjects were comfortably seated with the knee flexed and foot supported on a shoe-shaped platform and strapped in a position of 120° ± 5° plantar flexion. 29 Surface electrodes (circular discs 10 mm in diameter) with conducting gel were taped to the skin over the belly and tendon of the anterior tibial muscle. …”

“…28,29 Gold-plated surface electrodes (10-mm diameter; Grass Medical Instruments, Quincy, MA) were used to stimulate the peroneal nerve. A 3 × 5 cm oval surface coil was also taped to the belly of the anterior tibial muscle.…”

“…To calculate metabolic concentrations, it was assumed that the sum of PCr and Pi concentration was constant and equal to 42.2 mmol/L. 29,36 The chemical shift of Pi relative to that of PCr was used to calculate intracellular pH. 12…”

“…34,35 Previous studies have shown that peripheral sources of fatigue are also important in spastic muscles. 24,29 Lenman et al suggested secondary changes in spastic muscles are similar to those of immobilization and disuse. 24 In another study of a small number of patients with various types of spastic paraparesis, greater changes in energy metabolites accompanied the excessive muscle fatigue observed in patients compared to controls, which suggested that intramuscular factors may contribute to fatigue in spastic paraparesis.…”

“…24 In another study of a small number of patients with various types of spastic paraparesis, greater changes in energy metabolites accompanied the excessive muscle fatigue observed in patients compared to controls, which suggested that intramuscular factors may contribute to fatigue in spastic paraparesis. 29 Recently, in patients with MS, we have observed both reduced muscular oxidative capacity, 19 Therefore, the main objective of this study was to investigate muscle fatigue in MS patients, and to determine the extent to which muscle fatigue was related to clinical status and perceived fatigue. We examined fatigue in a group of MS patients and in healthy control subjects by measuring muscle force, activation, and energy metabolism during electrical stimulation of the anterior tibial muscle.…”