The authors investigated the risk of developing dementia for persons aged 50-75 years who suffered from Parkinson's disease, epilepsy, or severe head trauma. They compared the risk in this patient group with the risk in a reference group in a follow-up study based on the linked databases of three Dutch nationwide morbidity registers over the years 1980-1989. The overall relative risk of developing dementia within 8 years in patients with Parkinson's disease who were initially free of dementia was 3.0 (95% confidence interval (CI) 2.9-3.1). Risk was especially increased in younger Parkinson's disease patients (relative risk (RR) = 13.2, 95% CI 6.2-28.6). For patients with epilepsy, the overall relative risk was 1.5 (95% CI 1.4-1.7). Severe head trauma was not associated with an increased risk of dementia (RR = 1.0, 95% CI 0.9-1.1). These findings suggest that Parkinson's disease is an important risk factor for dementia, with a particularly high risk in young patients with Parkinson's disease. Patients with epilepsy may bear a moderately increased risk of developing dementia. This study does not support earlier findings in retrospective case-control studies of an increased risk of dementia in head trauma patients.

Extrahepatic biliary atresia (EHBA) is an infrequent disease confined to early infancy. Its aetiology is not clear, but an infectious agent has been implicated. Demonstration of a time-space clustering would support this hypothesis. Therefore, we investigated the time-space distribution of all 89 cases of EHBA born in a 10-year period in the Netherlands. We carried out a similar study in West Germany and analysed 130 cases of EHBA, born between 1969 and 1986, from 4 paediatric surgical centres. Analysis of these cases did not reveal any evidence for clustering in specific years or in a specific period of the year. The places of birth of the patients also were randomly distributed over rural areas, villages and towns. Neither did a method to reveal time-space interaction give any support for clustering. This random distribution of patients with EHBA suggests that EHBA could be pathogenetically a heterogeneous disease.

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The influence of early diagnosis on sight and survival was studied in 130 patients with bilateral retinoblastoma. Nineteen patients died of this condition. Statistical analysis predicted that 12 of these 19 early deaths could have been prevented if doctors' delay had been less than 1 week. Consequently, a reduction of 65% in mortality is possible. Similarly, statistical analysis also predicted that the number of patients with resulting blindness could be reduced by 40%. Central registration and monitoring of retinoblastoma families would greatly improve early diagnosis.

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