Periodic limb movement disorder

Periodic limb movement disorder (PLMD) is characterized by the occurrence, during sleep of repetitive, highly stereotyped, limb movements (PLMS), with a frequency >15/h (in children >5/h) associated with a clinical sleep disturbance or a complaint of daytime fatigue that cannot be better explained by another cause. A differential diagnosis is required between PLMD and insomnia with excessive daytime sleepiness resulting from restless legs syndrome (RLS) mimics that should rule out the diagnosis of PLMD. PLMD is generally considered to be a rare condition; however, recent data seem to indicate that it might be underdiagnosed. The exact cause of PLMD is not known; however, it is hypothesized that central dopamine may be involved in the pathophysiology of PLMD, given the known treatment efficacy on PLMS of l-dopa and dopamine agonists. A significant association between PLMS and a variant of an intron of the BTBD9 gene on chromosome 6p21.2 has been ascertained that may imply a developmental defect in the sensory-motor spinal organization. Treatment for PLMS can be the same as for RLS and it is expected to effectively reduce the PLMS index; however, studies specifically designed for PLMD are insufficient and treatment is based on clinical judgment. Most information available largely overlaps with that on RLS; however, even if PLMD might be, at least in some cases, a form of RLS or its presenting symptom, it certainly deserves specific attention, diagnosis, and treatment.