A longitudinal study of motor subtypes in delirium: Frequency and stability during episodes

Abstract

Objective

Motor-defined subtypes are a promising means of identifying clinically relevant patient subgroups but little is known about their course and stability during a delirium episode.

Methods

We assessed 100 consecutive adult palliative care patients with DSM-IV delirium twice weekly during their episodes using the Delirium Motor Subtype Scale (DMSS), Delirium Rating Scale-Revised-98 (DRS-R98) and Cognitive Test for Delirium (CTD). DMSS subtypes were assigned for each assessment and analysed for stability within patients during episodes.

Results

Across all assessments (n = 303; mean 3 per patient, range 2–9), subtype occurrence was hypoactive (35%), mixed (26%), hyperactive (15%) and no subtype (24%). “No subtype” was associated with significantly lower DRS-R98 severity scores, of which 80% were subsyndromal, whereas mixed subtype assessments were the most impaired on the DRS-R98 and CTD. Subtypes were stable within delirium episodes in 62% of patients: 29% hypoactive, 18% mixed, 10% hyperactive and 6% no-subtype. The DRS-R98 noncognitive subscale scores differed across groups whereas cognitive subscale scores did not (p < 0.001).

Conclusions

We conclude that motor subtypes occur in nearly all patients with full syndromal delirium and are often stable during an episode. Subtypes exhibited comparable levels of cognitive impairment but differed in non-cognitive symptoms, supporting the importance of cognitive testing to detect delirium in less overt cases.

Introduction

Although delirium is considered a unitary syndrome with prevalent core symptoms, it is a heterogeneous condition for causation and outcome, especially across the major age ranges. Those with hyperactivity are more readily recognised but this may contribute to poorer outcomes among hypoactive cases. Meagher [1] reviewed the evidence that delirium patients described according to motor/psychomotor subtypes are reported to be associated with differences for prognostic parameters. However much of the literature utilised different subtype criteria and symptom severity thresholds such that subtype incidence and outcomes are inconsistent across studies [2]. Notably, referral samples are usually confounded by significant under-recognition of hypoactive patients which affects the accuracy of study results. Drug treatment response differences for motor subtypes have been addressed in only a few studies [[3], [4], [5], [6]] but differential psychopharmacology has not yet been clearly delineated.

Moreover, interpretation of the existing literature is hindered by a lack of consistency in methodology. Motor subtype checklists include many nonspecific behavioural symptoms, may only require one symptom for a subtype to be present (and that might not be specifically motor in nature), and have not been validated against controls or objective motor measures. Motor activity items from rating scales have also been used in some studies and tend to focus on pure motor disturbances in their definitions. Meagher et al. [7] validated a new motor subtype scale, the Delirium Motor Subtype Scale (DMSS), focused only on motor features and which differentiated delirious from nondelirious subjects. Moreover, subsequent work has indicated that DMSS defined subtypes match objective (electronic) measures of motion [8]. Subtypes identified cross-sectionally using the DMSS had comparable neuropsychological profiles but differed for noncognitive symptoms of delirium [9]. Furthermore, preliminary work has suggested that the DMSS has predictive validity for outcome in delirium [7]. No other delirium subtype method has undergone such rigorous validation.

Most phenomenological research describes cross-sectional assessment of delirium and therefore little is known about the stability of motor symptoms and subtypes over the course of a delirium episode within an individual [1]. To fully capture the character of the syndrome, which includes fluctuations in severity over a 24-hour period, phenomenological issues must be explored with longitudinal studies that assess clinical profile throughout the duration of an episode. The increased interest in longitudinal study of delirium has highlighted that the course of delirium is much less reversible than traditional concepts have emphasised and that a significant number of patients experience persistent symptoms that can progress to long-term cognitive impairment [10] although the relevance of factors such as variations in underlying aetiology, ageing, genetic factors and treatment settings in shaping illness course over time remains uncertain [11].

We describe 100 consecutive cases of DSM-IV diagnosed delirium occurring in a palliative care setting that were assessed for motor profile, cognition and delirium phenomenology longitudinally for up to 9 visits (6 weeks) during the course of their delirium episodes. The specific aim of this report was to explore how motor profile (DMSS subtype) evolves during delirium episodes and relates to delirium syndromal severity using well-validated tools. In particular, we wished to determine [1] the intra-individual stability of motor subtype classification [2] whether the frequency of motor subtypes changes with increased duration of delirium (e.g. whether more persistent illness involves greater prominence of hypoactive profile [3]) the extent to which mixed subtype overlaps over time with hypoactive and hyperactive subtypes. A separate report addresses the relationship between motor subtypes and aetiology, medication exposure and prognosis [12].