Background: Cognitive deficits occurring with dementia are frequently not reported by the affected subject. Therefore, informant reports from close relatives are especially important for the early diagnosis of dementia. Internationally, the Informant Questionnaire on Cognitive Decline in the Elderly (IQCODE) has been evaluated with positive results and is a widely used informant-rated instrument for the diagnosis of cognitive decline. For the German speaking countries, norms and evaluation of the psychometric properties of the instrument are lacking.
Methods: Norms for the German long version of the IQCODE were established with 46 healthy elderly married couples. These were compared with respect to their concurrent and discriminative validity with groups of patients suffering from mild cognitive impairment (MCI, n=25), Alzheimer's or mixed dementia (AD, n=59) and frontotemporal lobe degeneration (FTLD, n=15).
Results: The German version of the IQCODE exhibited good psychometric properties and was able to best discriminate between cognitively intact and demented subjects with AD. Receiver-operating characteristic analyses indicated a cut-off score of 3.38 which corresponds well with the value given in international literature. Patients with MCI and with FTLD were also reliably distinguished from cognitively intact subjects. However, the instrument did not distinguish AD from FTLD with any significant degree of confidence.
Discussion: The German version of the IQCODE reliably discriminates cognitively intact persons from those suffering from MCI or cortical dementia, but not between different types of cortical dementia, such as AD and FTLD. The IQCODE is an efficient informant-rated screening instrument for the early diagnosis of cognitive decline and dementia.