The assessment and identification of delirium motor subtypes is clinically important because these subtypes may differ in terms of the severity of symptoms,¹ etiology,² pathophysiology,³ and outcome.⁴⁵ In addition, delirium is misdiagnosed or detected late in half to two-thirds of cases, which leads to delayed treatment.⁶ Delirium is likely to be misdiagnosed as psychosis, mania, or akathisia in patients with the hyperactive or mixed subtypes, and as depression or dementia in patients with the hypoactive subtype.⁵

Altered motor behavior in patients with cognitive disturbance has long been recognized, with the ancient Greeks describing “agitated phrenitis” and “lethargicus”.⁷ Since the introduction of terms such as “hyperactive”, “hypoactive”, and “mixed” in the contemporary literature,⁸⁹ there have been new approaches to define motor subtypes using different methods.^4101112 However, attempts to categorize the subtype have produced heterogeneous results due to differences in the populations assessed and the methods used to define motor subtypes. In a more recent study, commonly used methods^9101113 were compared and the authors reported just 34% concordance between the methods within the same population.¹⁴

To develop a valid instrument to assess motor subtypes of delirium, the Delirium Motoric Checklist (DMC)¹⁴ was developed by combining 30 features from three existing psychomotor check lists.⁹¹⁰¹¹ Among these 30 features, 11 were identified as specific to patients with delirium and correlated with the Delirium Rating Scale-Revised-98 (DRS-R98),¹³ which resulted in a new motor subtype scale called the Delirium Motor Subtype Scale (DMSS).¹⁵ The DMSS focuses on “pure” motor symptoms rather than psychomotoric symptoms. Other studies have shown that the DMSS has good concurrent and predictive validity compared with objective methods for measuring motor activity, including electronic methods such as accelerometry.¹⁶ In addition, the scale is simple enough for use by both medical and non-medical staff.

In Korea, there has been no study of the DMSS, although some authors have investigated the associations between the delirium motor subtype and the severity of delirium and clinical characteristics.¹⁷

Therefore, the aim of this study was to develop a Korean version of the DMSS (K-DMSS) and investigate the validity and reliability of this scale among elderly patients with delirium.

The aim of the present study was to validate the K-DMSS in a sample of elderly patients with delirium admitted to a general hospital.

There have been numerous attempts to assess the motor symptoms of delirium with psychomotor checklists.⁹¹⁰¹¹ Previously, authors have used several delirium severity scales, including the Delirium Rating Scale (DRS),²³ DRS-R98,²⁴ Memorial Delirium Assessment Scale (MDAS),²²⁵ and Richmond Agitation/Sedation Scale.²⁶ In some cases, clinical observation has been used to identify the delirium subtype.²⁷ However, reported findings have been heterogeneous because of the lack of a standard method with a clear cutoff value and the use of instruments assessing non-motor symptoms. Meagher et al. compared the identification of delirium subtypes with various common methods⁹¹⁰¹¹ and the DRS-R98,¹³ finding just 34% concordance.¹⁴ Subsequently, they used items from these various assessments and combined them to create the DMC. From 30 items, they selected 11, that were specific to patients with delirium, and investigated correlation between them and motor items of the DRS-R98. This process created a new assessment, the DMSS.¹⁵ The latter allows more precise detection of motor subtypes than other methods by purely focusing on motor symptoms. In addition, it is a simple and easy scale that can be used by non-medical staff, and has been demonstrated to have concurrent and predictive validity.¹⁵¹⁶²⁸

More recently, the amended DMSS was developed by adding “increased speed of actions” to hyperactive items, and “decreased volume of speech” to hypoactive items, following investigation of hospitalized patients referred to consultation-liaison psychiatry.²⁹ Later, an abbreviated version of the DMSS (DMSS-4)³⁰ was presented for brief use in clinical settings where time constraints were present, and this was highly concordant with the original DMSS.

In terms of reliability, our results show that Cronbach's alpha coefficient for items included in the K-DMSS was 0.79, indicating good internal inconsistency. Furthermore, Cohen's kappa coefficient was 0.86, indicating good inter-rater reliability. Therefore, we demonstrated that the K-DMSS is reliable. Indeed, our results suggest slightly higher reliability than those reported in a validation study by Slor et al.³¹ in which Cronbach's alpha was 0.72.

To evaluate validity, we classified delirium motor subtypes with the K-DRS-R98 and Liptzin & Levkoff criteria, because both have been commonly used in previous studies. Cohen's kappa coefficient for the motor subtypes was 0.81 between the K-DMSS and K-DRS-R98, and 0.78 between the K-DMSS and Liptzin and Levkoff criteria. Therefore, our results demonstrate concurrent validity between the K-DMSS and previously used measure. Validity was also higher than that reported in by Slor et al.³¹ in which Cohen's kappa coefficient was 0.73 between the DMSS and the DRS-R98. Regarding sensitivity and specificity, except for the sensitivity value (0.5) of the no motor subtype between K-DMSS and Liptzin & Levkoff criteria, the values ranged from approximately 0.80 to 1 (Tables 4 and 6), thereby yielding high accuracy of K-DMSS in classifying each motor subtype and comparing with previously used measures.

In addition, correspondence analysis was used to illustrate the correlations of each subtype with one another, as classified by each scale. In the graphical representation (Figure 2), the distance between each point represents the accordance of each subtype. Each subtype was visualized in the adjacent area. Therefore, the motor subtypes classified with the K-DMSS were concordant with those classified with the other methods.

According to the K-DMSS, the hyperactive subtype was the most common in the present study, affecting 50% of the sample. This is consistent with the results of Grover et al.³² who reported that the hyperactive subtype was most common at 50.15%, but not with the findings of Meagher et al.¹⁵ or Uchida et al.³³ who reported that the hypoactive subtype was most common, affecting 35% and 58% of their samples, respectively. Grover et al.³² studied hospitalized patients who had been admitted for various diseases and subsequently referred to consultant-liaison psychiatry as a result of delirium. In contrast, Meagher et al.¹⁵ and Uchida et al.³³ investigated patients who received palliative care or those with advanced cancer, who subsequently presented with symptoms of delirium. Such inconsistent findings may suggest that motor subtype classification may depend on the population characteristics.

In the present study, the hypoactive subtype was relatively less common than the hyperactive and mixed subtypes using all the three assessment methods. This subtype will less likely attract the attention of a caregiver or nurse because there will be less or no overt behavioral disturbance in patients with the hypoactive subtype.³⁴ In contrast, behavioral disturbances in the hyperactive subtype are obvious. As such, some patients with the hypoactive subtype may not have been referred for psychiatric care.

There are several limitations to the present study, which should be borne in mind when considering our results. First, we assessed patients with altered mental state, referred to the psychiatric consultation liaison service. As we did not objectively evaluate the previous mental state of patients and excluded patients with dementia on the basis of the information provided by caregivers, the association between delirium and dementia was not considered. Furthermore, as mentioned above, hyperactive symptoms may have been more detectable; however, hypoactive symptoms may not have been recognized as characteristic of delirium by physicians. This may have resulted in a selection bias. Further studies assessing patients from the time of admission may overcome these limitations. Second, the potential influence of prescribed medications, such as benzodiazepine, antipsychotics, anticholinergics, and opiates, during the assessment was not considered. Third, the scale required symptoms to be rated on the basis of behavior 24 h before the assessment. Nonetheless, it is likely that information provided by patients or caregivers may have referred to times before the previous 24 h. Finally, the sample size was small, and inter-rater reliability was only assessed in a subset of patients.

Nonetheless, to our knowledge, this is the first validation study of the DMSS in elderly Korean patients. Further work in various populations to determine the efficacy of the scale will contribute to our understanding of delirium and its detection, treatment, and prognosis. Furthermore, additional research is required using the various versions of the DMSS, which are continually revised.