PLMD is a sleep-related movement disorder characterized by the presence of PLMS and by clinical sleep disturbance that cannot be accounted for by another primary sleep disorder (30). The PLMS are considered responsible for sleep fragmentation and a complaint of EDS. However, PLMS are present in 6% of the general population and in more than 45% of adults aged 65 years or older (95). Also, there are a number of conditions other than RLS where PLMS are also recorded, for example, in about 45% to 60% with narcolepsy (96), 70% with RBD (97,98), 27% to 38% with OSA (95,99-101) and also in insomnia, sleep-related eating disorder (SRED), fibromyalgia, and attention deficit-hyperactivity disorder. Medications, for example, selective serotonin reuptake inhibitors, tricyclic antidepressants, lithium, and dopamine receptor antagonists are also known to precipitate PLMS. Low brain iron, as reflected by serum ferritin may also play a role. Thus, persistence of PLMS and related clinical sleep disturbance after adequate treatment of associated sleep disorder would be required for a diagnosis of PLMD in such cases. In patients with suspected SDB, pressure transducer airflow monitoring or esophageal manometry should be used to monitor breathing during PSG to reasonably exclude SDB as the direct cause of the PLMS. When independent PLMS are present in patients with SDB, a separate diagnosis of PLMD may be considered if the PLMS persist despite adequate CPAP or other therapy and a clinical sleep disturbance remains that is not otherwise explained. Also, PSG must be performed after the biologic effect of a medication or substance, for example, antidepressant, known to aggravate PLMS has ended. Thus, although PLMS are quite common, the exact prevalence of PLMD is not known. Also, the extent to which PLMS contribute to daytime sleepiness is still controversial (96,102,103).
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