Summary
Epidemiology
- Mean age of onset between 45-60
- Prevalence is 0.5-1% of the over 60’s in the UK
- 2nd most common neurodegenerative disease (after Alzheimer's)
Aetiology
Parkinsonism is most commonly caused by ideopathic Parkinson’s disease. There are rare genetic syndromes that also cause the condition, and several drugs have also been implicated. See differential diagnoses (below) for other conditions that can cause similar clinical features.
Pathology
Results from the loss of
dopaminergic neruons in the basal ganglia, most notably the
substantia nigra. Surviving neurons contain aggregations of protein (mostly
α-synuclein), called
Lewy bodies. In some cases, the Lewy bodies are seen throughout the brain – in such instances there is often co-existing
dementia.
Symptoms of PD are only seen once levels of dopamine are 20-40% that of normal. The degree of cell loss and akinesia is strongly correlated.
There is no obvious cause for this loss of neurons.
The disease is slowly progressive, without remission.
Clinical features
Parkinsonsim is often described as a triad of tremor, rigidity and bradykinesia. Signs are usually bilateral, although the initial presentation may be unilateral, and then progress.
- Tremor – usually of the hands @ 4-7Hz. Disappears with deliberate activity.
- Bradykinesia – slow movements. Fine motor movements are particularly badly affected
- Rigidity - increased resistance to passive movement. Sometimes called 'lead pipe rigidity'. Rigidity is equal throughout the range of movement (unlike spasticity – which is velocity dependent ). Rigidity is also equal in both extensors and flexors – unlike spasticity.
- Sometimes called cogwheel rigidity – as the rigidity temporarily gives in certain ranges of movement – as if you are moving a cog (the result of tremor plus rigidity).
- Note that power remains normal, and there is no sensory loss.
- Posture and Gait – slow shuffling steps gait. Often stooped, with reduced arm swinging. Narrow based.
- Speech – may be slow and monotonous. In late stage disease may be slurred, or even lost.
- Plain face / facial stare. This effect is exaggerated by a reduced blinking rate.
- Depression – many Parkinson’s patients also suffer from depression. If this is present in the early stages, then the plain face symptom of Parkinson’s may be confused with a withdrawn emotional state often seen in depression.
- Dementia – is also often associated with PD – probably because in many cases, the degeneration seen in the basal ganglia is also found in other areas of the brain.
- Hallucinations are common, and are thought to be a combination of both the disease and the drugs used to treat it. Often they are not unpleasant.
Differentials and other causes of Parkinsonism
- Alzheimers
- Multi-infarct dementia
- Repeated head injury e.g. in boxers
- The VODKA signs:
- V – vascular events – e.g. stroke, MI
- O – orthostatic hypotension with atonic bladder – can be caused by multi-system strophy (MSA)
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