Dementia


Provide a critical review of methods of estimate of


premorbid abilities in aging and dementia.


When a patient is first presented to a practitioner they are faced with the difficult task of measuring the amount of decline experienced by the patient. It successfully measure the amount of decline suffered one must have a test from which to compare the patients ability at present to that of premorbid functioning.


Carver (1990) found that reading ability highly correlates with the intellectual ability of the patient. It is generally thought that this may constitute an index of premorbid intellectual level in AD patients. This would allow for a comparison to be made as to the amount of decline in the patientís abilities. Nelson (1982) devised the National Adult Reading Test (NART), this can be used a predictor of premorbid abilities in cases of Alzheimerís disease. The NART test comprises of fifty multi-syllabic, low frequency words of irregular spelling-sound correspondence. The pronunciation of these words relies on retrieving knowledge from stored phonological information associated with corresponding orthographic information. It was thought that reading of irregular words was substantially preserved at and before the onset of Alzheimerís disease and remains relatively intact throughout the progression of the illness. The NART score shows evidence that the ability to transcode from orthography and phonology can be maintained for a long period in AD. Crawford, Hart and Nelson (1990) found that by using the NART they could have a good predictor of premorbid abilities as their research found very little difference between the scores of AD patients compared to those of the control group. When the Weschler adult intelligence score (WAIS) was obtained from the AD group and compared to the control group a large difference was found. The WAIS test comprises of different exercises that test the participantís ability to perform on tasks involving vocabulary, picture matching or locating similarities in a group of items, arithmetic, digit span memory, picture completion and picture arrangement. It was hoped that these scores combined would provide a relevant intelligence score of the patient at present, this is because it tested a wide range of abilities that are thought to deteriorate during the stages of Alzheimerís disease. Once calculated it gives a good impression of the state of decline in the patient. It is expected that once the two scores are compared a good pre and existing IQ can be obtained. In the research by Nebes, Martin and Horn (1984) the AD group scored significantly lower than the control group on the WAIS, suggesting that the NART score was a good predictor of premorbid functioning in the patient and the WAIS a good predictor of the present mental functioning of the patient. In other studies the Mini mental state examination (MMSE) by Folstien, Folstien and McHuge (1975) has been used instead of the WAIS. The MMSE contains similar tasks to the WAIS such as picture completion it also includes questions about patientís self knowledge of situation (questions like where are you? and what is the date? etc) it also like WAIS includes digit span and memory recall. The MMSE correlated with NART scores and dementia in Patterson, Graham and Hodges (1994) research. Similar yet less significant results were also found by Colombo, Brivio, Benaglio, Sili and Cappa (2000) when applying the MMSE to the TIB, (The Italian equivalent of the NART) Instead of using irregular words it relies on the lexical stress on multi-syllabic words. Words with regular stresses that fall on the penultimate syllable are seen as normal words and words with stresses at the end of a word or beginning of a word which are less frequent in the language are the irregular words. It would appear that WAIS scores correlate more strongly with the NART scores in predicting level of decline than the MMSE and NART scores do. Colombo et al (2000) found that when their NART scores were correlated with the WAIS scores the result had greater significance than MMSE scores did. When the NART was first devised it was thought that reading abilities did not decline in the onset of Alzheimerís disease. However, there is research that suggests there is deterioration in patientsí reading abilities as the disease progresses to the later stages which could lead to an under