Monday, January 27, 2014

DSM-5 Neurocognitive Disorders and Implications for Forensic Evaluations

As you’re probably well-aware, the latest edition of the DSM has been met with much criticism.  Concerns of over-diagnosis have been loudly expressed by individuals such as Allen Frances, M.D.  Despite receiving less attention than some other categories (i.e., personality and neurodevelopmental disorders), the changes to the diagnostic criteria for neurocognitive disorders have not escaped controversy. 

An article by Izabela Z. Schultz (2013) in Psychological Injury and Law discussed how the updated criteria for neurocognitive disorders may affect forensic situations.  Even with the focus on forensic applications, many of the concerns she raises apply to any type of neuropsychological evaluation (it should be noted that she also has positive things to say about the changes; I am focusing on her criticisms here).  Below I outline and respond to some of these concerns. 

In DSM-5, Major and Minor Neurocognitive Disorder diagnoses depend on the presence (or absence) of both a decline from previous functioning and inference with independence in activities of daily living.  The former consists of both concern from an individual (i.e., client, clinician, or family member) along with objective cognitive impairment, generally determined by neuropsychological testing.  Schultz cites problems with the assessment of ADLs and with the use of neuropsychological tests in this context.  First, she claims that psychologists may not have the skills to assess ADLs, given that this is primarily the domain of occupational therapists.  Although OTs specialize in ADL assessment, I’m confident psychologists are also capable of assessing ADLs through interviews and measures such as the Texas Functional Living Scale.

Schultz’s complaints about the use of neuropsychological testing for the purposes of determining cognitive impairment include:

1.      Arbitrary cut-off values (in standard deviations from the mean) may result in overdiagnosis of mild neurocognitive disorder and underdiagnosis of major neurocognitive disorder.
2.      Neuropsychological measures may have psychometric problems and be prone to biases, errors, and limitations with regard to certain populations who experience barriers to assessment. 
3.      Neuropsychologists administer several tests, and there is no standard rule for how to determine the overall level of impairment when test scores vary.  In forensic settings, this could lead to consciously or unconsciously-biased diagnostic decision making.
4.      DSM-5 does not stress a multi-method approach involving qualitative methods in addition to quantitative ones.

Related to Schultz’s first point is another criticism: lack of a “moderate neurocognitive disorder” diagnosis.  Schultz is concerned that in forensic settings, individuals who have serious functional problems may only be diagnosed with the mild disorder, which could detrimentally affect case outcomes.  She raises a valid point when she discusses the fact that DSM-5 acknowledges mild, moderate, and severe TBI when there is no option to diagnose a moderate neurocognitive disorder.  On the other hand, the cut-off values for establishing cognitive impairment (1 or 2 standard deviations for minor and major neurocognitive disorder respectively), are indeed somewhat arbitrary.  Adding a moderate diagnosis would reduce the range between the cut-off values, likely blurring the lines between the disorders even more.  Despite there being no option to diagnose a moderate neurocognitive disorder, I am not overly concerned about overdiagnosis of the mild form.  These diagnoses are not based solely on neuropsychological test scores – they also take decline from previous functioning and independence in ADLs into account.  Therefore, someone will not be diagnosed with a disorder based solely on scoring a standard deviation below the mean on a neuropsychological measure.

Schultz’s second and fourth points above appear to be less a problem with diagnostic criteria and more of an issue of neuropsychologists’ ethics.  Neuropsychologists are ethically obligated to choose tests that are valid for the purpose they are testing and for the individuals whom they are testing.  Therefore, the responsibility is on the psychologist to consider the psychometric properties of each measure.  Similarly, DSM-5’s lack of emphasis on qualitative assessment methods is not a problem.  Any competent psychologist knows that test scores must be interpreted in light of other factors such as premorbid functioning, clinical interview data, medical records, etc.

The third potential issue with neuropsychological testing could certainly bring about some problems.  It appears to be left up to individual clinicians to determine how to judge overall severity when multiple measures are administered with varying results.  For example, should an individual with one test that is two standard deviations below the mean, with the rest being just one standard deviation below the mean be diagnosed with major or minor neurocognitive disorder?  A standard rule does seem to be indicated here.  At the least, neuropsychologists should apply their own rule and use it consistently to avoid bias in forensic situations.

Another point of contention to the DSM-5 changes brought up in the article is the choice of specifiers for individual sources of cognitive impairment.  Schultz points out that rare diseases such as prion disease are included, while other sources such as Multiple Sclerosis and electrical injury are left out, relegated to the “due to another medical condition” specifier.  In forensic settings, it seems that use of “due to another medical condition” specifier shouldn’t be a problem, howeverm as the psychologist could discuss what that medical condition is probably causing the problem (e.g., an electrical injury).  Admittedly, I’m not a forensic psychologist, so maybe someone well-versed in that field could clear up this question. 

Finally, Schultz mentions that ADLs are considered in the diagnostic criteria, but not other domains of impairment, such as vocational or social impairment.  I agree that these should be part of the criteria, especially considering that functional impairment can be independent of other indicators such as neuropsychological test scores.  As an example, an individual with a 1 standard deviation decline in cognitive functioning due to a TBI may experience more functional problems if that individual has a cognitively demanding job as opposed to a job that requires only manual labor. 

Overall, I believe this category is one of the few which improved with the new edition of the DSM.  However, only time will tell how the updated criteria will affect neuropsychological evaluations in forensic and other settings. 

American Psychiatric Association. (2013). Diagnostic and statistical manual of mental disorders (5th ed.). Arlington, VA: American Psychiatric Publishing.

Schultz, I. Z. (2013). DSM-5 neurocognitive disorders: Validity, reliability, fairness, and utility in forensic applications. Psychological Injury and Law, 6, 299-306.

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