Defining the boundaries of the response of sleep leg movements to a single dose of dopamine agonist

STUDY OBJECTIVES: To define which leg movements (LM) associated with restless legs syndrome (RLS) respond to dopamine-agonist treatment and verify if they fall within current diagnostic criteria for periodic LM during sleep (PLMS). DESIGN: Single-blind placebo-controlled study. SETTINGS: Sleep laboratory. PATIENTS: 43 consecutive untreated patients with idiopathic restless legs syndrome. INTERVENTIONS: Patients underwent clinical and neurophysiological evaluation, hematological screening, and 2 consecutive full-night polysomnographic studies. Before the second polysomnographic study, all patients were randomized to receive 0.25 mg of pramipexole or placebo. MEASUREMENTS AND RESULTS: LM parameters such as duration, amplitude, interval, and periodicity were analyzed. Compared to placebo, pramipexole significantly (P < 0.01) reduced PLMS while increasing sleep efficiency. Specifically we observed a significant (P < 0.01) reduction in LM ranging 2-4 s in duration and with intermovement interval of 6-46 s and a significant decrease in the periodicity of motor events. No effect of pramipexole was observed on isolated LM. CONCLUSIONS: These results support a heterogeneous basis for LM in RLS patients; while isolated LM do not respond to pramipexole treatment, most, but not all, PLMS classified by means of the current criteria do. Further studies with different pramipexole doses or dopamine agonists with different receptor-binding preference are warranted to better define the borders of dopamine response of PLMS.