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Incidence of Parkinson's Disease

 

Clinical bottom line

Most developed countries with northern European age structures tended to have incidence rates between 12 and 20 cases per 100,000 per year.


Reference


D Twelves et al. Systematic review of incidence studies in Parkinson's Disease. Movement Disorders 2003 18: 19-31.


Systematic review

The review used MEDLINE and EMBASE, with searching to the end of 2001. Articles for inclusion had to be full publications of original studies providing an incidence rate for a whole population for idiopathic Parkinson's disease, or for Parkinsonian symptoms including Parkinson's disease.

Results

Twenty-five incidence studies were found, looking at populations throughout the world, and with populations as low as 8,000 to just under four million, though the number of incident cases was seven and about 400 (Figure 1).

Figure 1: Incidence of Parkinson's disease in individual studies

The determination of the diagnosis was mixed, with some patients seen by a specialist, varying from 30% to 100% of cases. Definition of incidence was also mixed, some studies using date of diagnosis, others date of onset, some both, and some did not give a definition. Also mixed in the studies were the diagnostic criteria used for defining Parkinson's disease.

In most studies the peak incidence was between 70 and 79 years of age, though mean age of symptom onset was 60-65 years in eight studies and over 65 years in five studies. There tended to be somewhat more men than women diagnosed (rate ratio ranged from 0.9 to 2.0).

The crude incidence per 100,000 per years ranged from 2 to 26 cases. Lower crude incidence rates came from populations in China, Libya, and Sardinia. Most developed countries with northern European age structures tended to have incidence rates between 12 and 20 cases per 100,000 per year.

Comment

Here we have an interesting study that not only gives some insight into the incidence of Parkinson's disease, but that also give an insight into the difficulty of such studies, and the need for strict criteria to ensure quality.

With Parkinson's disease, which develops predominantly in older people (Figure 2), the age structure of a population would be expected to be critical to any result. A young population would have low incidence, while an older population would have a higher incidence.

Figure 2: Parkinson's disease incidence and age

The authors of the study give a list of criteria for improving the quality and consistency of incidence studies: