Huntington's Disease
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Introduction
The Case of...
a simple case introducing clincial presentation and calling for a differential diagnosis. To get students thinking.
Causes and Risk Factors
1/10,000 Canadians affected
- autosomal dominant
- huntingtin gene on chromosome 4
- mutation is expansion of a CAG repeat -
- 10 - 26 in normal people
- 27 - 35 inconclusive
- 36 - 120 in affected people
- the higher the number of repeats, the earlier the age of onset
- though there may contributions from environment; variations among families
- mutation is unstable and often expands though generations - anticipation
Pathophysiology
- CAG expansion disorder (>44) in the huntingtin gene (Ch 4); the bigger, the worse
- thought to result from glutamate cytotoxicity, acting on NMDA channels and resulting in increased calcium influx
- loss of GABAergic neurons in the basal ganglia striatum
- increased activity in the globus pallidus externa, leading to increased inhibition of globus pallidus interna and thereby increased activity in the thalamus and subsequent cortex
expanded chain leads to aggregation
Signs and Symptoms
- chorea
- behavioural-psychiatric disturbances
- cognitive impairment
- memory retrieval (frontal subcortical)
- death
- history
- physical exam
History
- onset of symptoms ~30-50 years of age, though juvenile onset also occurs
- progressive over 15-20 years
- as disease progresses, patients lose a lot of weight for unknown reasons. People become non-verbal and bedridden, though comprehension seems to remain. Chorea is usually replaced by dystonia and bradykinesia.
- triad of symptoms:
motor
- involuntary movements/chorea
- impairment of voluntary movements
- leads to reduced manual dexterity, slurred speech, swallowing difficulty, problems with balance
- rigidity and spacticity in later stages
cognitive
- disorganization
- lack of initiation
- perserveration
- impulsivity
- changes in behaviour
- difficulties with spatial perception
- attention
- language
- learning and memory
- timing
psychiatric
- depression
- irritability
- apathy
- anxiety
- suicide
- obsessive-compulsive disorder
- schizophrenia-like disorder
- delerium
Physical Exam
Investigations
- lab investigations
- diagnostic imaging
Lab Investigations
predictive testing available
- tests at-risk, asymptomatic individuals
- need referral - mostly GP-mediated but self can also refer (anonymously?)
- covered by health care system
- long wait times at Maritime Medical Genetic Clinic (sp)
- series of 3-4 appointments over 3-4 months
- results can be interrupted at any point
- individual must choose freely
- asymptomatic children should not be tested
Session 1
- benefits and risks, person's concerns
- alternatives to testing
Session 2
- explore motivations and discuss implications for care, family unit
- make specific plans for day of results - who will know, who will come, what the
- other HCPs involved
- neurology consultation
- blood sample collected
- phone conversation prior to session 3
- results remain in sealed envelope
Session 3
- no chit-chat or distractions
- do you still want results?
- go
- can also be done by TeleHealth, ie with GP present
- patients love this : saves a lot of driving around
Session 4
- session 4 - follow-up, connecting with ie neurology
Diagnostic Imaging
Differential Diagnosis
Treatments
- there is no cure for HD
- some interventions may improve quality of life
- medication for depression and movement disorders
- communication and swallowing therapy
- physical therapy
- occupational therapy
- nutritional therapy
- recreation therapy (music, art, hobbies, etc)
Consequences and Course
can be extraordinarily isolating, both from community and within family
Resources and References
Huntington Society of Canada
Three main goals:
- resource centres
- education
- research
resource centres
- mail-outs to patients
- referrals
- navigation of system and community supports
- home visits
- assisting in planning ahead
- outreach to areas of province
- in-services to LTC facilities, other health systems
Topic Development
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