Sleep disorder may forecast gait problems in Parkinson’s

By Eleanor McDermid, Senior medwireNews Reporter

The findings of a polysomnography study have strengthened the link between rapid eye movement (REM) sleep behavior disorder (RBD) and Parkinson’s disease (PD), suggesting that it is specifically associated with freezing of gait.

The researchers found that tonic muscle activity during REM sleep in PD patients was increased in those with freezing of gait to a point similar to that of patients with RBD.

“Previous studies have shown that the severity of tonic RSWA [REM sleep without atonia] in RBD is predictive of the development of PD,” say lead study author Aleksandar Videnovic (Northwestern University, Chicago, Illinois, USA) and team.

“Our findings extend and refine this hypothesis by suggesting that the presence of excessive tonic [electromyogram] activity during REM sleep may be predictive of development of a subtype of PD that is dominated by [freezing of gait].”

Tonic muscle activity during REM sleep was elevated threefold in 10 PD patients with freezing of gait relative to 10 patients without, at respective averages of 30% and 10%, and about eightfold compared with 10 healthy controls.

Indeed, their tonic muscle activity was closer to that of 10 patients with RBD, in whom it averaged about 35%.

“These findings provide evidence suggesting that the pathophysiologic mechanisms that mediate [freezing of gait] in PD share a common subset of neurodegenerative changes that mediate RSWA in RBD,” the team writes in Neurology.

The differences persisted even after excluding four PD patients who already had a diagnosis of RBD from the analysis, showing that increased tonic muscle activity distinguished patients with freezing of gait even in the absence of obvious signs of the condition (ie, dream enactment).

There was a similar pattern for phasic muscle activity, although this was less marked, with the difference between the two groups of PD patients being nonsignificant. The researchers say this is consistent with a previous study showing that tonic rather than phasic muscle activity is the main predictor of PD in patients with RBD.

In an accompanying editorial, Linda Hershey (University of Oklahoma Health Sciences Center, Oklahoma City, USA) and David Lichter (University at Buffalo School of Medicine, New York, USA) say that further studies are needed to determine if RSWA is more strongly predictive of early- than late-stage freezing of gait.

But they agree that RSWA “may be useful as a potential biological marker in longitudinal studies of premotor or motor PD progression.”

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