3.4 The neuropsychology of Huntington disease (Snowden 2017) Flashcards
Huntington’s disease (HD)
An inherited degenerative disorder of the brain, caused by a expension in the number of CAG repeats in the huntington gene on chromosome 4.
Inheritance is autosomal dominant and is fully penetrant.
Thus, children of an affected parent, both male and female, have a 50% risk of inheriting the gene.
Symptoms appear around 40 years. Duration of illness to death is about 15-20 years.
Neuropathology of HD
HD is a degenerative brain disease, involving progressive atrophy of the brain.
- Earliest site of pathology is the neostratium, which consists of the caudate nucleus and putamen.
- Mutated Huntington protein = CAG repeat mutation = assumed to have a toxic function causing neuronal death.
- When the disease progresses there is more widesprad brain atrophy which causes loss of structural and functional connectivity between stratium and other parts of the brain.
Clinical characteristics HD
- Motor, cognitive and neuropsychiatric
- chorea: rapid involuntary movements of the face, trunk and limbs (most characteristic feature)
- Dystonia: slow twisting movements of the limbs.
- Bradykinesia: slowed execution of movements, and limb rigidity
- Juvenile HD (occurs in childhood): associated with prominent bradykinesia than with chorea.
Neuropsychological features
Psychomotor slowing
Initial alteration and most reliable indicator.
This decleration is frequently observed in timed assessment such as Stroop.
Cognitive decleration manifests in the early stages of HD before visible symptoms emerge and is considered a notable predictor of daily functional capacity.
Neuropsych features
Executive skills
Problems in planning, organisation, sequincing, cognitive flexibility and set shifting.
Wisconsin card sorting test test cognitive flexibility.
- Difficulty in multitasking
- problems in attention
- Automatic tasks require more attention
Neuropsych features
Memory
Difficulties in:
- Memory difficulties.
- Poorer free recall and cued recall
- More passive learning strategies
- Problems in source memory
- Prospective and declerative memory
- Producal memory
- Tasks involving motor skill learning, serial reaction time and sequence learning.
Neuropsych features
Emotion processing and social cognition
Emotion difficulties with:
- Processing facial expressions of emotion
- Particularly with emotion of disgust, anger and fear.
- Also affecting recognition of vocal emotions
- Deficits in emotion processing contribute to the social breakdown and reduction in sympathy and empathy.
Social breakdown, difficulties with:
- Interpersonal relationships
- Reduced flexibility in adapting to the needs of others
- Impaired regulation of behaviour in accordance with social conventions.
- Poorer “theory of mind”, which requires attribution of intentions, beliefs and mental states, recognition of socially inappropriate behaviour and sarcasm.
Some problems with social cognition occur before motor symptoms.
Neuropsych features
Other cognitive domains
- Speech production becomes less intelligible
- Difficulty coping with complete syntax
- Impairments on language tasks
- Difficulty with high-level perceptual discrimintion, perceptual integration, and constructional tasks which make executive demands
- Problems with mental rotation
- Problems in executive function
- Problems with everyday function and level of independence and quality of life,
Neuropsychiatric features
- Apathy (correlates with motor, cognitive and functional markers)
- Irritability (most troublesome behaviour of HD, commonly treated with SSRIs)
- Depression (can worsen apathy, social withdrawal, cognition, functioning and quality of life, suicidal ideation (8%))
Early symptoms: loss of motivation and drive
Later: irritability and loss of temper control worsen
Late stage: decrease of irritability and loss of temper.
Neurospsych assessment
- Mostly diagnosis on the basis of family history of HD
Huntington’s disease rating scale= widely used screening instrument for HD, and it consists of three tests, which are timed:
- Verbal fluency
- Symbol digit modality
- The Stroop task
European Huntington’s disease network (Euro-HD)
European-wide network for research into Huntington, had adopted letter and category fluency, symbol-digit modality, and Stroop tests as “core” components of their recommended neuropsychological test battery.
Treatment of HD
Incurable
- Tetrabenazine: for involuntary movements –> but it may increase depression
- SSRI: for irritability
- Cognitive interventions: aim to support and enhance neural compensation.
- Education family members.
Characteristics that are important in intervention
- HD pat’s require extra time for everyday tasks
- HD pat’s are forgetful but do not have classical amnesia, they have potential to benefit from memory aids.
- Automatic tasks (like walking) require more conscious attention. It is important voor HD pat’s to focus on one activity at a time.
- HD pat’s may not initiate activities but with encouragement can engage succesfully in them and experience enjoyment.
