Replication analysis for composition of the Delirium Motor Subtype Scale (DMSS) in a referral cohort from Northern India

The Delirium Motor Subtype Scale (DMSS) was developed by discerning the best differentiating motor activity symptoms from the Delirium Motor Checklist (DMC), a compilation of psychomotor symptoms from other subjective scales. To broaden its validation we replicated the original work done in a palliative care population in a psychiatric referral population. 100 consecutive C/L Psychiatry referrals with DSM-IV delirium in an Indian general hospital were assessed with the Delirium Rating Scale-Revised-98 (DRS-R98) and DMC and compared to 60 nondelirious hospitalized controls. Disturbances of motor activity were almost invariably present in patients with delirium and at a much higher frequency than in nondelirious control subjects. Principal components analysis identified 5-factors for the DMC where Factor 1 explained 37.3% of the variance and correlated significantly with DRS-R98 motor items. Items loading at >0.65 were selected for the replication scale if they also either correlated significantly with DRS-R98 motor items or were significantly more frequent in delirious patients vs. controls. The resultant scale comprised 12 items (five hyperactive and seven hypoactive) and was similar to the original DMSS. Combining motor items from the original DMSS and replicated version produced a 13-item amended DMSS that may have broader generalizability than the original DMSS.