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Severity of Alzheimer's disease and effect on premorbid measures of intelligence.

OBJECTIVES
To assess the robustness of the National Adult Reading Test (NART), Wechsler Test of Adult Reading (WTAR), Cambridge Contextual Reading Test (CCRT), Spot the Word (STW), and a demographic regression equation in estimating premorbid ability in people with Alzheimer's disease (AD).


DESIGN
A cross-sectional multiple measures design.


METHOD
Sixty-six probable AD participants were classified into stages of severity according to their Mini Mental State Examination (MMSE) score (minimal 24 to 28; mild 14 to 23). Their scores on the NART, WTAR, CCRT, STW and a demographic equation were compared with 32 healthy age matched controls.


RESULTS
Significant between-group differences were found for the tests of reading ability (NART, WTAR and CCRT). The mild group made significantly more errors than the control and minimal groups. For the mild group, there was an advantage of putting the NART words into context (CCRT), but this group still made significantly more errors than the control and minimal groups. The NART was compared with the demographic estimate and there was a significant difference for the mild group with the demographic estimate providing a higher estimate. This was not the case for the control or minimal groups. There was no significant difference between the groups on the lexical decision task (STW).


CONCLUSION
Reading of irregular words is compromised in AD for those with a MMSE score in the range of 14 to 23. A lexical decision task may provide a more accurate estimate of premorbid intelligence in those with mild AD. Further research is needed to provide evidence of STW's correlation with current ability.