Restless legs syndrome: impact on sleep-related breathing disorders

Restless legs syndrome (RLS) is a common chronic sensory-motor neurological disorder that remains a clinical diagnosis. Most RLS patients present with sleep complaints in the form of initiation and/or maintenance insomnia as RLS has a circadian rhythmicity. An increased number of periodic leg movements during sleep (PLMS) is a supportive criterion in the diagnosis of RLS. Abnormalities in the central dopaminergic and iron systems are involved in the physiopathology of RLS. There is a higher prevalence of RLS and PLMS in sleep-disordered breathing patients, particularly those with obstructive sleep apnoea (OSA), the most common sleep disorder in western societies. The complex mechanisms underlying the association between OSA, RLS and PLMS remain unclear. Untreated OSA can lead to adverse cardiovascular consequences due to cardio-metabolic dysfunction. It remains controversial whether RLS could further adversely impact the cardiovascular consequences of OSA. The PLMS do not have an additive effect on the hypersomnia experienced by some sleep-disordered breathing patients. Continuous positive airway pressure (CPAP) therapy is the most effective therapy for OSA. The presence of PLMS during CPAP treatment could be a marker of an incomplete resolution of sleep-disordered breathing in the form of increased upper airway resistance syndrome, despite treatment. Dopaminergic agonists are the preferred agent for the treatment of RLS, and are indicated when RLS symptoms are frequent and affect quality of life. PLMS and RLS do not seem to contribute to the residual hypersomnia that can be observed in some sleep-disordered breathing patients despite adequate compliance and effective CPAP therapy.