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Rahkonen et al 1 examine the complex issue of outcome after an episode of delirium and, in particular, whether an episode acts as an indicator of undetected dementia. Poor cognitive outcomes, including dementia, are well recognised after delirium but it is unclear whether delirium is merely a marker for dementia or if an episode contributes to the development of enduring cognitive impairment, possibly by a neurotoxic or kindling-type mechansm. Patients with mild cognitive impairment were not excluded at the outset but it is clear that there was a relation between mini mental state examination (MMSE) scores immediately after resolution of DSM IIIR delirium and risk of subsequent dementia. Given that persistent symptoms are common in delirium,2 one possible explanation is that these cases reflect unresolved subclinical delirium or that incomplete treatment of delirium is a risk factor for subsequent cognitive decline.3 The data should allow estimation of the frequency of dementia in those patients with MMSE scores within the normal range after full resolution of DSM IIIR delirium. This information is highly relevant to planning of postdelirium management and although the MMSE does not provide a sensitive measure of the neuropsychological disturbances of delirium, may shed some light on whether these findings relate to persistent cognitive deficits of delirium that are measured on the MMSE.
Rahkonen and Sulkava reply:
We thank Meagher for his interest and for his comments on our paper. In the Kuopio delirium study, the disappearance of delirium (according to the DSM-III-R) was ascertained carefully. Instead of being discharged to their own homes (after the treatment of delirium and its underlying causes) the patients were transferred to a rehabilitation centre. During the 7 to 14 days stay in the rehabilitation ward the disappearance of delirium was confirmed. However, some symptoms also appearing in delirium, such as disturbances of the sleep-wake cycle or mild memory deficits, may have still been detected in these elderly patients, but they did not fulfil the diagnostic criteria for delirium any more.
In the Kuopio delirium study, 27% of the community dwelling elderly patients without serious predisposing factors for delirium were diagnosed as having mild dementia immediately after the resolution of the delirium. The rate of subsequent dementia in the remaining non-demented patients was three out of 11 (27%) with the initial score on the mini mental status examination 24 or over after the delirium subsided (the incidence rate of dementia was 18.2/100 person-years). In the patients with an MMSE score less than 24 the rate of subsequent dementia after resolution of delirium was 11 out of 26 patients (42%) (the incidence rate of dementia was 25.4/100 person-years). However, in our article we published only the rate of the subsequent dementia in all the patients. The number of patients in the groups based on the MMSE scores was small and the usefulness of the scores in diagnosing dementia was limited in these elderly patients (mean age 82 years). In our study, no corrections were made to the scores of the MMSE test because of vision or hearing impairment or limited education.
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