Mental Capacity: Cognitive Deficit and Neurological Assessment.

There are occasions when a person's cognition is compromised to the extent that their mental capacity to make specific decisions may be impaired. Such scenarios sometimes occur when a person acquires a brain injury, degenerative condition or neurological disease or when the person has a severe learning disability or mental illness. 

Assessments of capacity can be conducted by the carer or health professional who initially raises concerns, however, what is often required is a thorough neuropsychological assessment including a measure of the person's current cognitive status conducted by a clinical psychologist or neuropsychologist. 

Neuropsychological assessment involves the integration of theoretical and clinical knowledge accrued from the study of brain behaviour relationships and information gleaned from the review of individual patient's medical records, patient presentation, patient interview, carer/relative assessment and the administration of standardised psychometric assessments. 

It is important to note that capacity cannot be inferred solely from standardised psychometric assessment but it is much more holistic. There are no performance cut-offs or black-and-white guidelines for assessing capacity. Psychometric tests will be chosen on the basis of the tests own reliability and validity credentials; on the basis of the anticipated cognitive deficits implicated by the pathology of the disease or insult; and often based upon the type of decision that has been examined. For example if the decision is one that involves the examination of ability to use judgement, executive tests measuring judgement may be chosen. Each neuropsychological assessment is therefore tailored to the situation. There are however certain helpful things to think about when conducting an assessment of capacity: 

1. Start off by thinking that everyone can make their own decisions. 

2. Give a person the support he/she needs to make decisions before concluding that he/she cannot make his/her own decisions. 

3. Nobody should be stopped from making a decision just because others may think it is unwise or eccentric. 

4. Anything done for, or on behalf of, a person without capacity must be in his/her “best interests” - a decision which is arrived at by working through a checklist. 

5. When anything is done or decided for a person without capacity, it must be the least restrictive of his/her basic rights and freedoms.

There is a duty by the assessor to ensure every avenue has been exhausted to facilitate a persons ability to make decisions, however following this, someone will fail to meet the requirements of capacity if they cannot fulfil all these prerequisites:

1: understand the information relevant to the decision

2: retain that information

3: use or weigh up the information

4: communicate the decision

Often a clinical psychologist or neuropsychologist will be instructed by the court of protection or a solicitor to conduct a neuropsychological assessment and produce a report to help the court make a decision as to a person's capacity and best interests. The instruction of these expert witnesses will offer an independent, evidence-based, reliable and valid opinion as to persons mental capacity on a specific decision(s). As well as being decision-specific, assessments are also time bound and subject to review depending on the prognosis and changeability of the person's cognitive status. For example, when a person recovers from severe mental illness /brain injury or where a person has periodically lucid periods within a neurological disease (sometimes seen in Parkinson's disease).

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Neuropsychology of Huntington's Disease

Huntington's Disease (HD) is a genetic degenerative disorder, normally of middle adulthood onset typified by three neurologic deteriorations upon cognition, movement and psychiatric health. The disease is eventually fatal and there is no known cure. 

The movement disorder consists of chorea involuntary movements which are often sudden, irregular and purposeless/semi-purposeful. Often this includes extremities first such as facial grimacing, eyelid elevation and neck movements followed by shoulder, trunk, and leg movements as the disease progresses.

Neuropsychology can provide expertise with the assessment of HD's cognitive and psychiatric effects. The neurological pathology of HD is best conceptualised as a subcortical process of degeneration. Imaging evidence suggests initial metabolic underactivity in the caudate. Atrophy has also been consistently imaged through MRI in this basal ganglia structure and often in the putamen and thereafter in the wider structures of the basal ganglia and the striatum. Although HD is regarded as a subcortical degenerative disorder the striatum is heavily networked in to the frontal lobes and therefore executive function is often affected in addition. 

As HD can now be genetically detected and anticipated through generation research has studied prodromal stages of HD patients. It now appears cognitive changes in rigidity of thought and depression may preclude the first visible chorea by a decade or more. Sensitive psychometric tests for early indications include executive tasks, particularly stroop and counting backwards in sevens from 100.

The cognitive profile of HD includes underperformance in speed of information processing, visuo-spatial processing, concentration and executive function. Although learning and memory is often affected in HD in comparison to other cortical dementias, such as alzheimers, the nature of the deficits is slightly different and HD is less typified by features such as aphasia, amnesia, or agnosia.

Cognitive changes in HD are now regarded as the most disabling of the triad of degenerative areas. HD's deleterious effect upon implicit memory (remembering how to do things) causes significant disability and this is exponentially compounded by HD's biological causation of loss of awareness and insight. HD sufferers also tend to experiences particular difficulties with splitting attention and retrieving memories without the benefit of prompting and support.

The psychiatric changes involved in HD mean that people who have not had hereditary history available often become misdiagnosed. Psychiatric symptoms often include mood dysregulation and mood disorder. 

Positive psychiatric symptoms manifest in a significant minority to include paranoia, thought disorder and hallucinations. Part of the perpetuation of these beliefs is thought to be exacerbated by other people's responses to HD's unusual features, particularly the facial grimacing, reduction in socio-emotional processing and mood dysregulation. 

Mood stabilising and antidepressant medication has some limited benefit and often this helps to lessen the risk of suicide, which is of statistical increase in HD populations. Psychotherapeutic intervention is compounded by cognitive changes, particularly executive deficits and loss of insight. 

Results of cognitive assessments can sometimes be helpful to HD patients but sometimes total loss of awareness makes this impossible. However, carers often benefit from the feed back of neuropsychological assessment and particular clarification of the organic nature of the unawareness, rather than understanding the person to be in emotional denial.