Attention-deficit–hyperactivity disorder (ADHD) is one of the most common childhood psychiatric disorders, estimated to affect 5–10% of school-aged children worldwide.1 According to the Diagnostic and Statistical Manual of Mental Disorders – Fourth Edition – Text Revision (DSM-IV-TR),2 ADHD is defined by a persistent and age-inappropriate pattern of inattention, hyperactivity–impulsivity or both. Onset before the age of seven years and impaired functioning in two or more settings are required for the diagnosis. Impairing symptoms of ADHD may persist into adulthood in up to 60% of cases.3
Restless legs syndrome (RLS) is a sensorimotor disorder characterised by an irresistible urge to move the legs, which is often accompanied by uncomfortable sensations in the legs or, less frequently, other body parts. These sensations are relieved by movement and are worse in the evening or night and when resting. The diagnosis of RLS is based on the revised criteria developed by the International Restless Legs Syndrome Study Group (IRLSSG).4 Although RLS has traditionally been considered to be a disorder of middle to older age, several case reports have shown that it may occur in childhood.5 However, children may report RLS symptoms differently from adults, in part because of their limited ability to describe RLS sensations. In addition, the clinical presentation of RLS may differ in children. Considering these particularities, the IRLSSG has proposed a set of criteria specific to children.4
Polysomnographically, RLS may be associated with periodic limb movements in sleep (PLMS) in about 80% of patients, in both adults and children.4 PLMS are defined as movements that occur in series of four or more, lasting between half a second and five seconds, have an amplitude of one-quarter or more of the toe dorsiflexion during calibration and are separated by intervals of four to 90 seconds. RLS per se and/or associated PLMS may lead to significant sleep fragmentation. Therefore, RLS is a recognised, although sometimes overlooked, cause of insomnia.