SPECT imaging of striatal pre- and postsynaptic dopaminergic status in restless legs syndrome with periodic leg movements in sleep

Restless legs syndrome (RLS) is a common sleep-related disorder principally characterised by leg paresthesia associated with an irresistible urge to move. A majority of RLS patients experience periodic leg movements during sleep (PLMS) and wakefulness. Pharmacological evidence suggests that RLS-PLMS maybe caused by a central nervous system dopaminergic (DA) dysfunction. The aim of the present study was to evaluate the striatal pre- and postsynaptic DA status in patients suffering from both RLS and PLMS, by means of [I-123]beta-CIT and [I-123]IBZM SPECT respectively. Ten drug-naive patients and ten age-matched controls participated in this study. All participants were recorded for at least one night of polysomnography before the SPECT studies. No difference was seen in DA transporter ([I-123]beta-CIT) binding between RLS-PLMS patients (MD=4.89) and controls (MD=4.81; p=0.81). The study of the striatal D-2-receptor binding ([I-123]IBZM) revealed a significantly lower binding in patients (MD= 1.72) compared with controls (MD=1.85; p=0.006). These results support the hypothesis that a central DA dysfunction is involved in the physiopathology of RLS-PLMS. Several mechanisms may be responsible for the decrease of the D-2-receptor binding. However, since [I-123]beta-CIT binding is normal, a decreased number of D-2-receptors or a decreased affinity of D-2-receptors for [I-123]IBZM is more likely than an increased level of synaptic DA with attendant down-regulation of D-2-receptors.