Abnormal motor behavior during sleep.

Abnormal motor behaviors during sleep can be classified into four categories, ranging from myoclonic jerks to complex and integrated motor behaviors There have been recent developments in several of these conditions, in particular restless legs syndrome (RLS) and rapid-eye-movement sleep behavior disorder (RBD). RLS is one of the major causes of insomnia. Familial aggregation of RLS has been demonstrated by several groups, and molecular genetics studies have suggested the presence of susceptibility genes on chromosomes 12q and 14q. Pharmacologic and brain imaging studies suggest the involvement of dopaminergic mechanisms in RLS, but recent work has focused on brain iron metabolism. Studies indicate that RBD patients may eventually develop Parkinson's disease (PD). Conversely, RBD has been found in patients already diagnosed with PD. Single-photon emission computed tomography and positron emission tomography studies have shown a decrease in binding to presynaptic dopamine transporter in both idiopathic RBD and PD. Patients with RBD (associated or unassociated with PD) also have neuropsychological deficits. RBD may therefore represent the prodrome of a neurodegenerative disease leading to multiple system atrophy and Lewy body dementia. Understanding the underlying pathophysiology of abnormal sleep motor behaviors may prove useful in the management of insomnia.