Psychometric evaluation of the DMSS-4 in a cohort of elderly post-operative hip fracture patients with delirium

Background: Delirium is a common neuropsychiatric syndrome with considerable heterogeneity in clinical profile. Rapid reliable identification of clinical subtypes can allow for more targeted research efforts. Methods: We explored the concordance in attribution of motor subtypes between the Delirium Motor Subtyping Scale 4 (DMSS-4) and the original Delirium Motor Subtyping Scale (DMSS) (assessed cross-sectionally) and subtypes defined longitudinally using the Delirium Symptom Interview (DSI). Results: We included 113 elderly patients developing DSM-IV delirium after hip-surgery [mean age 86.9 +/- 6.6 years; range 65-102; 68.1% females; 25 (22.1%) had no previous history of cognitive impairment]. Concordance for the first measurement was high for both the DMSS-4 and original DMSS (k = 0.82), and overall for the DMSS-4 and DSI (k = 0.84). The DMSS-4 also demonstrated high internal consistency (McDonald's omega = 0.90). The DSI more often allocated an assessment to "no subtype" compared to the DMSS-4 and DMSS-11, which showed higher inclusion rates for motor subtypes. Conclusions: The DMSS-4 provides a rapid method of identifying motor-defined clinical subtypes of delirium and appears to be a reliable alternative to the more detailed and time-consuming original DMSS and DSI methods of subtype attribution. The DMSS-4, so far translated into three languages, can be readily applied to further studies of causation, treatment and outcome in delirium.