The misclassification of periodic limb movement disorder: A systematic review applying research diagnostic criteria

Periodic limb movement disorder (PLMD) has been reported in the scientific literature for more than three decades. However, its diagnostic criteria have changed substantially over time, complicating cross-study comparisons and weakening the evidence base. In a companion paper, we proposed research diagnostic criteria (RDC) for PLMD in adults to operationalize current ICSD-3TR elements and support transparent classification in research settings. We systematically searched PubMed, Scopus, and Google Scholar from inception through April 2025 using predefined PLMD-related terms. We then applied modified RDC to classify PLMD status across all eligible published samples. More than half of the reviewed samples (55.6% of 180 samples from 149 studies) were incompatible with a PLMD diagnosis under contemporary standards, most often because of exclusionary comorbidities such as restless legs syndrome or untreated sleep-related breathing disorders. A further 28.3% could not be classified because critical diagnostic information was missing. Only 29 samples (16.1%) met criteria for possible or probable PLMD, and only four (2.2%) approached definite PLMD. These findings show that the diagnosis of PLMD has been applied inconsistently across diagnostic eras, resulting in widespread misclassification under current criteria. Clear diagnostic criteria and reporting standards are needed to build a reliable evidence base and advance PLMD research.