Subclinical Augmentation in Relation to Previous Dopaminergic Treatment in Patients with Restless Legs Syndrome: A Post Hoc Analysis of Two Randomized, Placebo-Controlled, Crossover Trials.

Background and objectives: Augmentation, a long-term complication of dopamine agonist treatment for restless legs syndrome (RLS), is preceded by a gradual loss of response. We investigated whether prior long-term dopaminergic treatment affects current and future responses to dopaminergic and non-dopaminergic drugs, which would suggest broader changes in RLS pathophysiology.

Methods: We retrospectively analysed two previously published, double-blind, randomized, crossover, placebo-controlled studies with the adenosine transport inhibitor dipyridamole and the orexin receptor antagonist suvorexant. Post hoc analyses compared responses between dopaminergic (DA)-naïve and dopaminergic (DA)-treated patients with RLS. None of these patients met the diagnostic criteria for augmentation. After a 2-week washout, patients received active treatment (10-20 mg suvorexant or 200-300 mg dipyridamole) or placebo for 2 weeks, followed by crossover. Efficacy was assessed using the International RLS Rating Scale (IRLS), Clinical Global Impressions-Severity scale (CGI-S), multiple suggested immobilization test (m-SIT), periodic leg movements of sleep (PLMS) and other polysomnographic measures.

Results: A total of 28 patients participated in the dipyridamole study (DA-pretreated, n = 10; DA-naïve group, n = 18), and 40 participated in the suvorexant study (DA-pretreated, n = 9; DA-naïve group, n = 31). Compared with DA-naïve patients, DA-pretreated patients responded significantly worse to both treatments on the basis of the IRLS, CGI-S, m-SIT, PLMS indices. There were no differences in sleep parameters.

Conclusions: Our results suggest that previous long-term dopaminergic treatment, even before clinical augmentation is reached, induces pathophysiological changes in RLS that impair future responses to both dopaminergic and non-dopaminergic therapies. Our findings confirm previous results with gabapentin enacarbil and suggest that these changes develop well before clinical augmentation appears. Pathophysiological implications for the understanding of dopaminergic augmentation are discussed. Our results support the American Academy of Sleep Medicine (AASM) recommendation against using dopamine agonists as the initial choice for RLS treatment.