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 c entral cholinergic systems are involved in PD. Electrophysiological investi gation showed decremental Muscle responses following repetitive nerve stimu lation (RNS). We hypothesized that fatigue in PD patients may be secondary to cholinergic defect at the neuromuscular level. Material and methods - Tw enty PD patients with disabling fatigue symptoms were enrolled. We used sti mulated single fiber electromyography (s-SFEMG) to evaluate the neuromuscul ar 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 10 0 constant consecutive single fiber potentials. The i-MCD values in each pa tient were averaged to obtain the mean MCD (m-MCD). Results - None of the 2 0 PD patients with disabling fatigue symptoms had an m-MCD over 29 mus or m ore than 10% of the i-MCD values over 41 mus. The neuromuscular junction wa s intact in terms of normal jitter (expressed as MCD) and an absence of blo cking. Conclusion - Our findings indicate that the cholinergic system at th e neuromuscular level is not affected in PD patients with fatigue symptoms.