Neuropsychological performance in early and late onset Alzheimer's Disease: comparisons in a memory clinic population.
Suribhatla S, Baillon S, Dennis M, Marudkar M, Muhammad S, et al. ;
Commented by , 24 Jan 2005
Aims
To compare the neuropsychological performance in patients with early onset (<65) versus late onset (>70) dementia.
Methods
All patients who had been assessed at the Leicester Memory Clinic 1995-2002 were included: in January 2001, the Clinic changed its policy to accepting patients primarily under age 65.
Notes were reviewed retrospectively by four Specialist Registrars in Old Age Psychiatry using ICD-10 diagnostic criteria. All patients had received a detailed multidisciplinary assessment including a battery of neuropsychological tests.
Statistical comparison of the two groups was by the Mann-Whitney U test, then logistic regression.
Results
185 patients were diagnosed with Alzheimer's Disease (AD) in the time frame; in 166/185 the standardised research diagnosis agreed with the memory clinic diagnosis. 32 cases were excluded as they were age 65-70, 4 excluded as they had a secondary diagnosis of depression, leaving 130 cases for analysis.
40 of these were early onset, 90 late onset/over 70. Accompanying cerebrovascular disease was reported in 5 of the early onset group, 21 of the late onset group. Both groups were similar in terms of gender, duration of illness, pre-morbid IQ and prescribed psychotropic medication.
Analysis of neuropsychological test score showed significant differences in CAMCOG (Cambridge Cognitive Examination) subscores. Early onset cases performed better on recent memory and abstract thinking, and significantly worse on attention and praxis, compared to the late onset group.
On the majority of neuropsychological tests there was no difference between the groups, with a trend for language function to be more impaired in the early onset group.
The late onset group performed better on WAIS (Wechsler Adult Intelligence Scale) digit span, AMIPB (Adult Memory and Information Processing Battery)Â complex design and the written picture description; the early onset group performed better on the WAIS similarities test and the Boston naming test.
Dr Seymour's comments
Much of the literature suggests that familial early onset disease, involving specific genetic abnormalities, has a rapid onset and progression, ie., is a more aggressive form of the disease with early language impairment. Does this also apply to the more common polygenetically determined disease that presents early?
The strengths of this study are the sample size, the group matching (by gender, severity of dementia, and pre-morbid IQ), and the rigorous diagnostic procedure.
The weaknesses - acknowledged by the authors - are the potentially biased sample (in a tertiary memory clinic), the retrospective analysis, and the fact that not all neuropsychological tests were administered to all subjects. Further, there were surprisingly few cases of mixed vascular and Alzheimer's dementia in their sample.
The main finding of this study was that both groups performed at a comparable level on most neuropsychological tests, including tests assessing language. After adjusting for overall dementia severity and pre-morbid IQ, there was greater fronto-parietal right hemisphere deficit in early onset; greater temporal/left hemisphere involvement in late onset.
However, these differences were quite subtle and did not support a simple right/left hemisphere distinction between early and late onset AD. The authors postulate that in early onset AD there is more symmetrical progression, resulting in greater right hemisphere involvement at any given level of severity.
Such differences in the spread of neurodegeneration may be due to the different genetic risk profiles at different ages (eg., via APO-E4 expression), or because co-morbid cerebrovascular disease in late onset AD effects clinical expression.