Parkinson's disease: the onset of symptoms
Onset
Trying to determine exactly when Parkinson's disease starts is extremely difficult and is complicated by a number of factors.
The onset of Parkinson's symptoms is usually subtle, although once a diagnosis has been made, the doctor may look back and wonder how it was missed. This means that the disease has probably been present long before it is actually diagnosed.
At diagnosis, about 60 per cent of dopamine in the basal ganglia and possibly 80 per cent of substantia nigra cells will have been lost. Before this, the brain can compensate and symptoms of Parkinson's are not noticeable. This means that the damage to the cells of the brain has been going on long before any signs can be seen.
Determining when Parkinson's starts can also be complicated because in the stage before diagnosis, the symptoms can be vague and non-specific and could be caused by other conditions. For example:
- joint pain could be caused by a frozen shoulder;
- tiredness could be a symptom of depression;
- forgetfulness could be the early stages of dementia;
- constipation and weight loss could be caused by cancer of the colon; or
- one-sided progressive weakness could be a symptom of a tumour.
Looking back
Doctors and patients often try to look back to date the onset of Parkinson's and this is also very difficult.
- Handwriting and home videos can be used in trying to back-date the onset.
- Tremor can appear very early, then disappear and '"go underground' for a period.
- Predictions made using scientifically based calculations and actual patient experiences give a different picture. If progression is calculated backwards and assuming that the loss of cells is more in the first few years, there would seem to be about a 4-6 year pre-symptomatic period after the disease begins and before any symptoms are noticed. Calculations using functional imaging also give a pre-symptomatic time of about 5-6 years.
- Listening to patients, many say that looking back, they can see signs of Parkinson's up to 20 years before they were diagnosed. For instance, Ray Kennedy, the UK football player was diagnosed at 34 and British TV footage shows symptoms in his arm at the time when he stopped playing and he also tells of difficulty smiling going back many years.
- Many people feel that their Parkinson's began at a particular time, often associated with some stress, injury or illness. One possibility is that there are pre-clinical signs which makes a person at risk but until they are exposed to the final trigger, which could unmask the condition, it does not become apparent.
- The sense of smell can be affected decades before diagnosis (scientists have shown that the smells of wintergreen and oregano are most affected). Damage to the sense of smell does not appear to get worse with motor symptoms and many people are not affected, so it cannot be used easily to pre-date the beginnings of Parkinson's.
Progression
Patients tend to say that the first few years of Parkinson's are relatively trouble free, but scientific studies show that, in general, the progression tends to be more rapid in the early years, then flattens out.
There is, however, no formula which can be used to predict progression, either in terms of the symptoms which a person will experience or the rate at which they will progress. Instead, there is a tremendous amount of variability. For example:
- the way the disease begins is variable, with different people showing different symptoms as the first signs of Parkinson's;
- the relative prominence of the various signs and symptoms varies from person to person;
- the age of onset varies from the 20s to the 80s;
- the rate of progression varies, with some people progressing much more rapidly than others;
- the degree of functional impairment does not progress evenly either in one person or over the whole Parkinson's population; and
- modern treatment has influenced the progression of Parkinson's, with more people living longer.
There is a challenge for researchers because of the potential for treatments that may stop or slow down the progression. In the future, there will be an increasing need to be able to not only determine when Parkinson's begins, but also to be able to predict those who are at risk before their symptoms become apparent.
Reference
: EPDA Conference, Barcelona 1998. 'When does Parkinson's disease begin?' Andrew J. Lees (London).
Last Reviewed: 22 July 2002
