Wednesday, 15 January 2014

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.  

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