The classical features of Parkinson’s disease are usually straightforward to spot:
What are the more subtle presentations to be aware of?
Are there any tests that can be done if there is a clinical suspicion of Parkinson’s disease?
What should you do, or who should you direct your patient to see?
The UK Parkinson’s Disease Society Brain Bank Clinical Diagnostic Criteria (Hughes et al. 1992) for diagnosing Parkinson’s disease are based on the presence of:
Bradykinesia - slowness of initiation of voluntary movement with a progressive reduction in speed and amplitude of repetitive actions - and at least one of the following:
A tremor at rest, at a frequency of 4-6 Hz
Postural instability not caused by primary visual, vestibular, cerebellar, or proprioceptive dysfunction.
However it is critical to exclude other conditions, which mimic Parkinson’s and this is a clinical challenge for many patients, their carers and their doctors, so it is important to see the right person.
Even though Parkinson's Disease affects the whole brain, and thus the symptoms can and will affect the whole body the initial symptoms of are often unilateral.
In tremor-dominant Parkinson’s disease, tremor may be the only feature at presentation.
In akinetic-rigid Parkinson’s, tremor is often absent, (akinesia is a severe lack of spontaneous movement, more severe than bradykinesia).
In the elderly, due to their other co-morbidities, bradykinesia and rigidity can be misdiagnosed as a normal consequence of ageing. Sometimes the only presenting symptom may be pain/stiffness, for example a unilateral “frozen shoulder” and the signs of Parkinson’s may remain subtle in the hands.
What happens on movement?
The resting tremor usually subsides significantly when the patient moves or on action; when the patient writes, the handwriting (without tremor) may however become progressively smaller and examining. Generally, patients or carers may have noted a slowing down, a change of facial expression (hypomimia), a slight change in posture (forward trunk flexion), painless dragging of one leg, or shuffling of both legs during walking.
Parkinson’s Disease is a Clinical Diagnosis
The patient has to be seen by someone experienced not only in Parkinson's disease but also the things that look like Parkinson's, the mimics. Only then can any tests be considered.
Tests have two purposes:
To exclude other disorders which might mimic Parkinson’s disease, and
Tests which are highly suggestive of loss of dopaminergic brain function.
Routine blood tests need to exclude general metabolic causes of 'slowing', for example anaemia, vitamin deficiencies, chronic renal or liver disease, calcium disorders and hypothyroidism. Also, hyperthyroidism should also be excluded for those with tremor.
A CT brain can indicate if further tests are required to assess chronic hydrocephalus or significant brain vascular disease.
For selected patients, if there is still doubt, MRI brain may help - it will pick up earlier disease if there is still doubt - though the scan is much longer, the patient must be able to lie very still and not suffer from claustrophobia.
DaTScan (a nuclear medicine, dopamine transporter scan) is not usually available in General Practitioner, but is available to Hospital doctors and Parkinson's specialists, who generally can choose the right patients to use the scan in, where the scan will give the most useful information. DaTScan measures the function of only the pre-synaptic nigro-striatal dopamine pathway - it is these neurones that carry dopamine, and when they are lost Parkinson's is one of the main causes.
The DatScan is Normal
A normal scan is seen when the process does not affect dopamine transporters, such as:
essential tremor, dystonic tremor or other dystonia (not all dystonia has tremor)
drug-induced parkinsonism and/or tremore
functional parkinsonism and/or tremor
The DatScan is Abnormal
If the DatScan is abnormal this confirms presynaptic dopamine dysfunction, but the scan cannot differentiate the various causes of this, which include: