Restless legs symptoms without periodic limb movements in sleep and without response to dopaminergic agents: a restless legs-like syndrome?

Patients fulfilling the essential criteria for restless legs syndrome (RLS), but in whom the response to conventional dopaminergic treatment and the presence of periodic limb movements in sleep (PLMS) are lacking, are occasionally encountered. The aim of this study was to systematically characterize this population. In a consecutive series of 117 patients fulfilling the essential criteria for RLS, we assessed the presence of the following supportive criteria: PLMS > 15/h on polysomnography, and favourable response to dopaminergic treatment. We differentiated patients with 'classical RLS' (RLS-C; fulfilling at least one of the selected supportive criteria) from those with 'RLS-like syndrome' (RLS-L) in whom supportive criteria were not fulfilled. There were 103 RLS-C and 14 RLS-L patients. Compared with RLS-C patients, RLS-L patients were significantly younger, more severely affected by RSL symptoms, and were more probably to suffer from psychiatric comorbidities, than RLS-C patients. This study proves the existence of patients with severe RLS symptoms, but without PLMS and without response to dopaminergic treatment, who are clinically distinct from patients with 'classical RLS'.