Provide a critical review of methods of estimate of
premorbid abilities in aging and dementia.

Rosie Ireson


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
patient's abilities. Nelson (1982) devised the National Adult
Reading Test (NART), this can be used a predictor of premorbid
abilities in cases of Alzheimer's 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 Alzheimer's 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 participant's 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 Alzheimer's 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 patient's
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 Alzheimer's
disease. However, there is research that suggests there is
deterioration in patients' reading abilities as the disease
progresses to the later stages which could lead to an under
estimated pre-morbid IQ. Colombo et al (2000) calculated the
severity of illness within the patients and then categorised
them from mild to moderate and severe depending upon their
assessment. Colombo et al (2000) found that the IQ level did
decrease with the severity of illness thus leading to a lower
premorbid IQ estimate. This shows that reading ability is not
totally resistant to change in the later stages of Alzheimer's
disease. Due to reduction in estimates of Premorbid IQ