NEUROPSYCHOLOGICAL ASSESSMENT: A CASE STUDY
Auckland Hospital, New Zealand
Dr Dorothy Gronwallwasis a consultant neuropsychologist at the Auckland Concussion Clinic, and had over twenty years experience and interest in the field of head injuries. Dr Gronwall had been appointed to the ACC Quality Review Board to oversee and advise on planning and research for management of head injuries, and the Scientific Review Committee of the Neurological Foundation.
Her sudden death from a stroke in November 2001 is a great loss. A trust fund has been set up to establish a
memorial prize for the top student in Clinical Neuropsychology at the University of Auckland. Donations may be sent to: The Dorothy Gronwall Memorial Prize Fund, University of Auckland Charitable Trust, Advancement Office, University of Auckland, Private Bag 92019, Auckland, New Zealand."
This paper was first presented to the Marjorie Gordon Memorial Seminar, Palmerston North, NZ in March, 1997, and published in SHADOWS (Journal of the NZIMRT) VOLUME 40, NO. 2, JUNE, l997.
Chronic exposure to neurotoxins can result in symptoms such as poor memory, problems with concentration, sleep disturbances, excessive fatigue, reduced impulse control and decreased initiative among other things.
For many years I have been assessing people who have a similar set of problems which result from the diffuse brain damage caused by closed head injury. Because of this experience I am sometimes asked to do a full neuropsychological assessment in cases of chemical neurotoxicity. This paper discusses what is involved in this, and what information an assessment like this can and cannot give you.
I intend to describe a typical case, and a typical set of results, but this case study is not about any one single person. Instead it is a composite based on results from several typical people. I have called this typical person Jane. What I shall do is describe the sorts of tests that are used, and how the results are interpreted.
It is obviously important first of all to get some idea of what sort of a person Jane was before she had any contact with neurotoxins. There are several ways this can be done, including the use of educational and occupational demographics.
Perhaps the most widely used method, and the one I prefer, is called the New Adult Reading Test (NART for short). This is based on the fact that the English language does not consistently use one letter or letters for each phoneme, and that many words such as 'ache' and 'quadruped' can only be pronounced correctly if you know them already. The test consists of a list of such words. The theory is that even if you have sustained so much brain damage that you no longer know what the words mean, provided that you can talk you will be able to say them if they were in your vocabulary before your injury or illness.
The estimate of pre-morbid ability is made on the number of words correctly pronounced, and it has been shown to correlate highly with both verbal and fullscale IQ in people who have not had brain damage. Jane's score places her in the above average intellectual ability group.
After the assessment of pre-morbid ability the general areas that need to be assessed are general intelligence, visual perception, memory, concentration and attention, language. executive functions and reaction times.
Most test batteries use a complex intelligence test such as the WAIS-R, but these are given in order to calculate lQs. On the contrary, it is totally invalid to deduce lQs from someone who has presented with cognitive problems, since this is likely to result in a greater than normal scatter of scores on the individual parts of the test. Combining all these individual scores to get a composite IQ is meaningless, and can actually be very misleading. In Jane's case she did well on all the sub-tests except the one sampling the ability for abstract reasoning, and on digit symbol.
The person doing this test is given a paper with a grid with the numbers one to ten printed across the page and a different symbol drawn in a box under each. The test itself consists of a list of single digits in random order with empty boxes below them, and the person is given a minute and a half to fill in as many of the symbol as possible. It is considered the most sensitive to any kind of brain damage because it is a complex task involving memory and visuo-motor co-ordination as well as the ability to work under time stress.
There are many different tests of ability for visual perception, including some in the WAIS-R. I use the Rey~Osterreith complex figure as well. This figure is not the Rey [not shown here], but it has a similar horrible muddle of elements so you can get a feel for the task. Jane was asked to copy the Rey as accurately as she could (Fig 1). Her copy was not well organised and was both inaccurate and incomplete. As a result her score was significantly below average for people of her age. However she had scored within the expected range on all the other perceptual tests, so it is probable that the low copy score was the result of poor frontal lobe function rather than because of a perceptual deficit.
The assessment includes a range of different memory tests looking at memory for words and narrative material as well as for visual, non-verbal material. Some tests look at the ability to recall the information after varying periods doing other tests. Jane scored in the expected above average range on a test of new verbal memory and on both immediate and delayed recall of prose passages.
However her memory for non-verbal material was significantly below average. One of the non-verbal tests that she was asked to do was to draw the Rey figure from memory thirty minutes after she had copied it, and another was that she was asked to fill in as many symbols on the bottom line of the digit symbol form with the key at the top covered.
Attention and concentration
As well as the basic Wechsler measures I generally include some other tests. The Trails Test has two parts. In Part A the subject is required to join up 26 circles numbered from one to 25 in numerical order. In Part B the circles contain letters as well as numbers and the task is to join them in alternating numerical and alphabetical order as quickly as possible. Jane's times were good average.
She was also given the more sensitive and more demanding Paced Auditory Serial Addition Test (PASAT). She was played a series of single digit numbers on a tape, and had to add them together in pairs, adding the first number to the second, the second to the third, and so on. Thus if the first five numbers were 6, 3, 5, 8, the answers would be 9, 8, 13. It is relatively easy to do this test for a short time, but each trail has 61 numbers, and it is impossible to concentrate sufficiently to get all 60 answers correct.
There are four trails, starting from a relatively slow one where numbers are heard every 2.4 seconds. Each trail is slightly faster than the last, and by the last trail the rate is twice as fast as the first. Jane coped with the two slowest trails, but her scores were significantly below average for people of her age on both. She became distressed when the third trail was played and the test was discontinued. This is a common reaction, and her performance indicates a significantly slowed information processing rate.
I do not consistently give an aphasia battery, and generally look at speech reception and production during the course of the session. I also look at automatic language such as reciting the alphabet. There was no evidence of impairment or of any naming or word-finding problem. However Jane did score significantly below average for her age and vocabulary level on the controlled word fluency test, where she was asked to say as many words as possible beginning with a given letter of the alphabet in a sixty second penod. In addition she showed a faster than normal falloff over time on task which is typically found in eases of frontal lobe dysfunction. She gave an average of more than three times as many words in the first thirty second penod than she did in the second half.
Executive functions refer to the ability to plan and to organise and to check what has been done, and to modify what is done depending on feedback. Both the Rey and word fluency had shown impairment in this area, consistent with impaired frontal lobe function.
I use a computer test for this which was developed at a rehabilitation centre in New York. It is a simple reaction time test, and all Jane had to do was press a key whenever the target appeared on the screen. Targets appeared in the peripheral visual fields as well as in the centre. Jane was consistently significantly slower than normal under all conditions, and was also signtlicantly slower than normal when she was responding to targets in the right visual field than to those on the left.
In most areas Jane scored at the good average level expected from the estimate of her pre-morbid ability. She did well on verbal memory tests, and her ability for new verbal learning was also at this level. The pattern of her test results was not consistent with any deficit in visual perception, and language skills and vocabulary were good.
However she was significantly impaired on measures of non-verbal memory, her ability to attend and to concentrate was significantly impaired, and her information processing rate was significantly slower than normal. Her reaction times were also significantly slowed, more so when she was responding to things on the right than to those on the left.
Finally, there was evidence of significantly impaired frontal lobe function, affecting her ability to plan and to organise and to monitor how she was doing.
What do these results tell you? The first is that they are not "normal" in the sense that this is not the pattern that is found in people who have no brain dysfunction. Some of the reasons why a neuropsychological assessment might produce results like this are as follows:
1. Intellectual handicap
This is very unlikely, for two reasons, apart from the fact that it is at variance with her history of normal schooling and normal vocational achievement. Firstly, good average scores were recorded on many tests, and secondly a test of pre-morbid ability estimates that Jane was of above average ability rather than retarded.
2. Poor motivation
Again this is unlikely, as it does not explain why she did well on some tests and not on others. Further, she did poorly even on tests that are more interesting to do, such as the computer-generated reaction time test, yet produced excellent scores on tedious tests such as tests of new verbal learning.
In other words, is it possible that Jane was manipulating her responses to back up her claim that she was impaired as a result of exposure to neurotoxins? She it an intelligent lady, and maybe she had done her homework and knew what sort of results she should produce. However, even if she had done this, she would be more likely to fake low scores on the verbal memory tests, as verbal memory deficits are very frequently reported in cases such as hers. Further, PASAT has a built in consistency measure, and even very sophisticated university students are unable to deliberately produce believable impaired scores. This is because it is a very demanding task and it is simply not possible to keep track of the score at the same time as doing the test.
It is natural that the sort of changes that Jane has noticed in her level of function would get her down a bit. Depression does lower the level at which people perform in a test session. However one would not expect to have only some of the tasks depressed, and others even difficult ones, ahove average. Further, while there is no doubt that depression slows reaction times it does not make sense that reactions to one peripheral visual field would be significantly slower than reactions to the other.
5. Closed head injury
Jane's test results are identical to those that could he produced by someone who had had a closed head injury, and obviously a history of head injury has to be excluded. In Jane's case she had never been knocked out. Interpretation is more difficult if there has been traumatic brain damage, even if this has been some time previously.
6. Substance abuse
Jane denies abusing alcohol, or taking any other mind-altering drugs. Even if we did not believe her, though, substance abuse is unlikely to have resulted in this pattern of scores-
7. Chronic fatigue Syndrome
Tapanui flu or ME are often subsumed under this heading, and certainly there are some similarities between Jane's results and those from chronic fatigue syndrome people. Information processing rate is typically slowed in CFS, for example. However verbal memory is also almost invariably found to be impaired, yet Jane had good scores on these measures. Finally, a recent review stated that no cases of CFS had ever been found to show impairment of frontal lobe function in spite of a wide variety of measures being used. Thus we can confidently state that Jane is not a CSF case.
The conclusion is that we have excluded mental retardation, malingering, poor motivation, depression, head injury, substance abuse and chronic fatigue syndrome as reasons for this set of results.
What we have NOT done is to diagnose chemical neurotoxicity as the cause. It is never possible to produce a definite diagnosis from a neuropsychological assessment. All that can be produced are probabilities, not certainties. So what I can do is to make the statement that these test results are entirely consistent with the history of chemical exposure. No neuropsychological assessment can ever give you proof that this is in fact the problem. What it does do is provide more evidence that adds to the probability of this being the causal factor.
Most of the neuropsychological literature focuses on assessment of the effects of exposure to neurotoxins and few address the issue of what to do about it. The latest issue of the journal Neuropsychological Rehabilitation describes a pilot study carried out in Sweden of a rehabilitation programme for such cases (Neuropsychological rehabilitation of patients with organic solvent-induced chronic toxic encephalopathy. A pilot study, Lindgren et al, 7 (1), 1997).
The subjects had all had 10 years or more of daily exposure to neurotoxins, but had had no exposure at all in the three months before the study. The patients took part in group sessions with four to seven people in each group, and were taken through both cognitive rehabilitation and group therapy sessions run by neuropsychologists and a social worker.
At the end of the trial, test results and some neurophysiological measures were used to measure the effect of this intervention, and both the patients and their families were given questionnaires to evaluate how useful they felt it had been. Positive results were found with each type of measure, and the authors conclude that the aim of neuropsychological rehabilitation should be ... to improve the patient's adaptation to the brain dysfunction and the secondary consequences and the patient's self-confidence, self-conception and everyday functioning.
It would certainly be worth a try.