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How are Neuropsychological Tests Used to Diagnose Mild Traumatic Brain Injury (MTBI)?Posted May 30, 2017
By Jonathan A. Karon
Neuropsychological testing is frequently ordered in cases of suspected brain injury. This is because even if brain damage can be seen on an MRI or CT scan or by some of the newer, more sensitive imaging studies, this will not tell you what effects the brain damage is having on the individual. The leading textbook on neuropsychological testing explains, “Even when the site and extent of a brain lesion have been shown on imaging, the image will not identify the nature of residual behavioral strengths and the accompanying deficits; for this neuropsychological assessment is needed.” Lezak, et al, Neuropsychological Assessment, 5th Edition, 2012 at p. 5.
Neuropsychological tests are a series of tests which are intended to diagnose different types of cognitive impairments. When the tests are developed, they are administered to a diverse group of persons, some with normal functioning and some with specific types of brain injuries. By comparing the difference in scores between non-impaired persons and those with cognitive impairments a scale can be developed that allows for the diagnosis of cognitive impairment.
As different types of brain damage produce different impairments, there are a variety of tests which are designed to diagnose different problems. Some neuropsychologists always administer the same tests, no matter what the suspected injury. This is known as the “fixed battery” approach. Other neuropsychologists will tailor the tests based on the suspected diagnosis. This is known as the “flexible battery” approach. In the case of a suspected mild traumatic brain injury (MTBI) the neuropsychologist is looking for a pattern of scores indicating impairments in attention, processing speed, working memory and executive functioning as these are associated with an MTBI. In contrast, other cognitive functions, such as long term memory, tend to be unaffected by a mild traumatic brain injury (you may remember what you learned in sixth grade, but not what you just had for lunch).
Interpretation of neuropsychological tests requires establishing a baseline. In other words, it is important that the neuropsychologist estimate a person’s pre-injury (the term used is “pre-morbid”) i.q. so that how a person should score on a test can be compared to how they do score. The concept is actually quite simple. Someone who scores in the 90th percentile in i.q. shouldn’t be scoring in the 50th percentile in executive function. On the other hand, if someone who has an i.q. in the 50th percentile scores in the 48th percentile in executive functioning, that probably doesn’t indicate a problem. In baseball terms (for the benefit of Red Sox fans) if David Ortiz can’t hit a curve ball, there’s something wrong, but if I can’t hit a curve ball, that’s just how I am. Baselines can be estimated from prior school records, work records, and test scores (SAT’s, LSAT’s, GRE’s, etc.) or if these are not available by inference from other neuropsychological test scores on cognitive domains that are not affected by a traumatic brain injury.
Because most MTBI sufferers will improve (at least to some extent), neuropsychologists will usually want to wait a certain period of time after injury before testing. One neuropsychologist with whom I’ve consulted, suggests that the optimal time periods for testing would be 90 days after injury, as most healing occurs within the first 90 days, with follow up testing at 18 months to evaluate potential permanent impairments. Others might draw the lines a little differently, but all would agree that early testing is unlikely to reflect permanent problems.
There is also a phenomena known as a “practice effect” which simply means that a person who has had previous neuropsychological testing is likely to do better on subsequent testing, which is another reason for spacing out the intervals between testing.
Unfortunately, there are limits to the usefulness of neuropsychological testing. Some people perform better on the tests than they do in the real world. This is why its always important to interview the patient as part of the exam and also, if possible to talk to their family members and possibly friends or co-workers to get an idea of their actual level of functioning. Also, there are no tests for many well recognized symptoms of a traumatic brain injury. These include headaches, fatigue, loss of social skills, personality changes, irritability, impulsive behavior and light sensitivity.
Finally, if you are going for neuropsychological testing, it’s important you try to do your best. Out of concern that some persons, particularly those with court cases, might try to appear more impaired than they are, neuropsychological testing usually includes one or more tests intended to determine whether or not someone is putting forth a sincere effort to do well. These tests are usually so easy that even someone with a brain injury should do well. Accordingly, if the scores on those tests are dramatically low, it may interpreted as intentional faking (referred to as “malingering”). It is recognized that someone might fail one of those tests for other reasons, but it’s still better if you don’t. More importantly, you want to be accurately diagnosed and this requires you try to do your best. Despite advances in imaging, neuropsychological testing remains an indispensable tool for diagnosing cognitive strengths and weaknesses due to a traumatic brain injury.
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