Purpose Delirium and dementia have overlapping features that complicate differential diagnosis. Delirium symptoms overshadow dementia symptoms when they co-occur, but delirium phenomenology in comorbid cases has not been compared to both conditions alone.
Methods Consecutive adults with DSM-IV delirium, dementia, comorbid delirium-dementia and cognitively intact controls were assessed using the Revised Delirium Rating Scale (DRS-R98) and Cognitive Test for Delirium (CTD).
Results Delirium and comorbid delirium-dementia groups had comparable DRS-R98 and CTD total scores, which were greater than in dementia or control groups. On the DRS-R98, multiple non-cognitive symptoms, inattention and disorientation were more severe in delirium groups compared with dementia-alone. Patients with dementia differed from both delirium groups on the CTD test of attention. Spatial span backwards was significantly lower in all patients with cognitive impairment (delirium, comorbid delirium-dementia, dementia alone) compared to controls, whereas spatial span forwards distinguished delirium groups from dementia.
Conclusions Delirium phenomenology is similar with or without comorbid dementia. A wide range of neuropsychiatric symptoms distinguish delirium from dementia. Spatial span forward is disproportionately diminished in delirium suggesting usefulness as a differentiating screening test.
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Funding This study was supported through departmental funds at Limerick Mental Health Services.
Competing interests Unrelated to this research, DJ Meagher has received research grant funding from Astra-Zeneca and has acted as an advisory consultant for Pfizer, Eli-Lilly, Bristol-Meyers and Janssen Pharmaceuticals, as well as receiving travel support from Smith-Kline Beecham, Eli-Lilly, Astra-Zeneca, Novartis, Wyeth and Bristol-Meyers Pharmaceuticals Ltd. T Trzepacz is a full-time salaried employee of Eli Lilly and Company and shareholder of Lilly. Lilly does not have a product with an indication for delirium. P Trzepacz owns the copyright for the Delirium Rating Scale-Revised-98 but does not charge a fee for its use except in for-profit situations.
Patient consent Obtained.
Ethics approval This study was conducted with the approval of the Midwestern Regional Hospital Ethics Committee, Dooradoyle, Limerick, Ireland.
Provenance and peer review Not commissioned; externally peer reviewed.