(BMJ module; information from Dr David Crawford, consultant in neuropsychiatric genetics at St Mary’s, Manchester. Module chosen as I have a patient with Huntington’s who is developing increasing problems.)
Huntington’s causes a combination of progressive motor, cognitive, and psychiatric symptoms. It’s also a catabolic disease, meaning that patients can lose a lot of weight in a short time (over and above that caused by swallowing difficulties).
It is probably the most slowly progressive of all the neurodegenerative disorders, with a typical course of around 15 to 25 years from onset to death. Typical age of onset is around 40 or soon after, but there is a huge range, with about 5% of cases showing up before age 21 (juvenile Huntington’s) and a small percentage starting only in their 60s or 70s.
- Hyperkinetic symptoms: involuntary movements which typically start with affecting the fingers and toes and, over a number of years, become larger in amplitude and begin to affect more central muscles (choreiform movements). Typically, these symptoms eventually plateau and then decline again as the hypokinetic aspects (see below) become more often.
- Hypokinetic symptoms: slowing of movement and reduced co-ordination.
- Dysarthria (difficulty speaking) often progressing to complete muteness in the late stages
- Slowing of thinking
- Impaired attention/concentration. (In the late stages, this can be severe enough to impair cognitive functioning almost completely, leading to a situation where a patient will have quite severe dementia but occasionally will have enough of a flash of concentration to come out with quite a cogent statement.)
- Difficulties with executive function (planning and organising, problem-solving)
- Mental rigidity and repetitive thinking (typically middle to later stages)
- Loss of motivation (eventually overwhelming)
- Irritability (very common, often one of the presenting symptoms)
- Low mood and anxiety
- Impulsive behaviour, impulsive anger
- Loss of drive and motivation (later symptom; eventually the most predominant)
- Chorea: dopamine-blocking or dopamine-depleting drugs (i.e. neuroleptics or tetrabenazine). Downside is that these worsen the bradykinesia and can slow thinking; tetrabenazine can also cause depression.
- Low mood/anxiety and irritability: SSRIs in high doses (typically top end of recommended range; may also need high doses mirtazapine at bedtime to augment).
- Late-stage irritability and aggression: neuroleptics (see above caveat).
- Catabolism: very high-calorie diet
- General support
Eventual death from intercurrent infections. It should be noted that, prior to this, patients can typically live out in the community (with appropriate support) for much longer than was previously the case, due to the better symptomatic treatment.