Michele Matarazzo
Neurologist specialising in Parkinson's disease at the Comprehensive Neuroscience Centre HM Cinac, editor-in-chief of MDS Podcast and coordinator of the Ad Hoc Committee on Neurotechnology, Innovation and Entrepreneurship of the Spanish Society of Neurology.
This is a very interesting article. These results had already been presented in at least one conference paper, but now we can evaluate them more comprehensively as the article provides all the methodological details.
It is a very solid study from a methodological point of view, although with the obvious limitation of being a retrospective population study in a cohort of US war veterans, mostly men and with a high burden of comorbidity. This type of design allows for the detection of associations that are difficult to study in small samples, thanks to the large number of subjects and the large amount of data available, but the main problem is always inferring causality. In other words, this well-conducted study confirms an association between sleep apnoea and Parkinson's disease, already described in previous studies, and adds a very suggestive finding: people with apnoea who start CPAP (continuous positive airway pressure) treatment earlier have a slightly lower risk of developing the disease. Although the authors have made a considerable statistical effort to minimise bias, we cannot be sure that this reduction in risk is directly due to the treatment; it remains a fascinating hypothesis, which adds to another study with similar characteristics that suggests a reduction in risk in patients with apnoea treated with airway surgery. Ideally, these results should be confirmed in prospective, controlled studies.
From a clinical point of view, and taking into account the low invasiveness and side effect profile of CPAP, as well as its proven positive impact on other complications of sleep apnoea, this study provides further evidence in favour of early diagnosis and treatment, even while we await definitive confirmation of its possible protective effect against Parkinson's disease.
In terms of mechanisms, these results open the door to speculation about how sleep apnoea treatment could reduce the risk of Parkinson's disease. Among the most plausible hypotheses are the impact of nocturnal respiratory disturbances on oxygen and carbon dioxide concentrations and their haemodynamic and metabolic consequences, as well as the role of sleep in the functioning of the glymphatic system, which is responsible for facilitating the removal of potentially harmful substances from the brain and is particularly active during sleep. All of this reinforces an important overall message: sleep disorders, and apnoea in particular, are not simply a problem of “sleeping poorly”, but can have significant repercussions on long-term brain health.