Sleep can benefit Parkinson’s patients, but we don’t know why

New research, published in the Journal of Parkinson’s Disease, has found that almost half of Parkinson’s patients experience sleep benefit. However, researchers have been unable to identify any significant variables between those who do benefit and those who do not.

Our understanding of sleep benefit, which the study defines as the report of a ‘clear decrease in Parkinson’s disease symptoms after a period of sleep’, is less than extensive. The fact that some patients experience better motor functioning after sleeping is surprising, as no medication can be taken during such periods.

The study, conducted by researchers at Radboud University Nijmegen in the Netherlands, asked 243 Parkinson’s patients to complete a screening questionnaire that gauged a range of motor and non-motor symptoms of the disease. The team, who analysed demographic and disease characteristics, depressive symptoms and quality of life, found that 46.9 per cent of respondents experienced sleep benefit. However, the results displayed no differences in demographic and clinical characteristics between those who did benefit and those who did not. There were no significant variations between factors such as age at onset, disease duration, type of treatment, depression, quality of life, memory, fatigue, apathy or sleep quality.

I spoke to Merel van Gilst from Radboud’s Donders Institute for Brain, Cognition and Behaviour, to find out more about the perplexing results of this study. I began by asking van Gilst whether it came as a surprise to find that the investigation had uncovered no significant variables.

"We know from the clinic that a lot of patients experience sleep benefit, but we were surprised by just how high the percentage of patients familiar with the effect was," she explained. "In previous studies on the subject, varying results were found on possible determinants of sleep benefit. In our study we couldn’t associate sleep benefit with any of these variables."

I went on to ask van Gilst whether the subjective nature of the experimental technique could have influenced the outcome of the study.

"It was a subjective study, based on patient’s reports" she conceded. "So we cannot be sure that there actually is a decrease in symptoms. To study this, we will have to use objective measures, and we are planning to do this in the future. Since our results (and those of most previous studies) were obtained via questionnaires, it is possible that some patients might have misunderstood certain questions. You can imagine that it would be easy to confuse sleep benefit with the refreshing effects of sleep."

Another interesting finding from this study was that both overnight sleep and daytime naps were reported by Parkinson’s patients to be of benefit. Regular daytime naps were taken by 98 of the respondents. Of these respondents, 46 per cent had no sleep benefit, 20.4 per cent reported benefiting from both daytime and nocturnal sleep, 20.4 per cent said that they only benefited from overnight sleep, and 13.3 per cent found that only daytime sleep was of benefit.

"Of course daytime naps are shorter than overnight sleep," said van Gilst, "but the sleep in itself is similar. We did expect to find some sleep benefit after daytime naps, but again, quite a high percentage of patients reported this effect."

According to van Gilst, she and her colleagues remain hopeful that they will be able to identify some the underlying cause of sleep benefit through future research. I asked her what was next in the search for this elusive explanation.

"Firstly, we would like to try to objectify the phenomenon and establish whether there really is an improvement in the symptoms," van Gilst explained. "We think that we will find objective decreases in symptoms, but maybe not to the extent that they have been reported in the subjective study.

"It would be very interesting if we could identify the cause of sleep benefit. Patients could be encouraged to take afternoon naps more often. If we study the subject even more, we could enhance our understanding of Parkinson’s disease and of the impact of sleep."