Evaluation of fatigue in Parkinson's disease patients with stimulated single fiber electromyography

OBJECTIVES: Fatigue is a disabling and dopa-resistant symptom in Parkinson's disease (PD). Pathological studies have shown that both peripheral and central cholinergic systems are involved in PD. Electrophysiological investigation showed decremental muscle responses following repetitive nerve stimulation (RNS). We hypothesized that fatigue in PD patients may be secondary to cholinergic defect at the neuromuscular level. MATERIAL AND METHODS: Twenty PD patients with disabling fatigue symptoms were enrolled. We used stimulated single fiber electromyography (s-SFEMG) to evaluate the neuromuscular junction of these patients. For every patient, at least 15 muscle fibers were tested at the rate of 10 Hz with the method described by Trontelj et al. The individual mean consecutive difference (i-MCD) was obtained from 100 constant consecutive single fiber potentials. The i-MCD values in each patient were averaged to obtain the mean MCD (m-MCD). RESULTS: None of the 20 PD patients with disabling fatigue symptoms had an m-MCD over 29 micros or more than 10% of the i-MCD values over 41 micros. The neuromuscular junction was intact in terms of normal jitter (expressed as MCD) and an absence of blocking. CONCLUSION: Our findings indicate that the cholinergic system at the neuromuscular level is not affected in PD patients with fatigue symptoms.