A new study by the University of Turku and Turku University Hospital, Finland, found that a significant proportion of Parkinson's disease diagnoses are later corrected. Up to one in six diagnoses changed after ten years of follow-up, and the majority of new diagnoses were made within two years of the original diagnosis.

A recent study published in Neurology reveals significant diagnostic instability in Parkinson's disease, with 13.3% of diagnoses revised over a 10-year follow-up period. When dementia with Lewy bodies (DLB) is treated as a separate diagnostic category, the revision rate increases to 17.7%.

The large-scale study followed over 1,600 patients initially diagnosed with Parkinson’s disease. The results demonstrate the ongoing difficulty of distinguishing it from other similar disorders, despite improvements in diagnostics.

“Notably, a majority of these diagnostic changes occur within the first two years of diagnosis, which emphasises the challenges and uncertainty clinicians face in diagnosing Parkinson’s disease accurately,” explains Valtteri Kaasinen, Professor of Neurology at the University of Turku and principal investigator of the study.

Clinical practices and diagnostic challenges increase misdiagnoses

Commonly revised diagnoses included vascular parkinsonism, progressive supranuclear palsy, multiple system atrophy, and clinically undetermined parkinsonism.

While dopamine transporter (DAT) imaging was frequently used to aid in diagnosis, the study found that postmortem neuropathological examinations were only conducted in 3% of deceased patients, with 64% of these confirming the initial Parkinson’s disease diagnoses. This decline in postmortem examinations mirrors a global trend seen in other studies.

The study also highlights the difficulty in differentiating between Parkinson’s disease and dementia with Lewy bodies, particularly in relation to the controversial "one-year rule."

“This rule, which considers the temporal sequence of motor and cognitive symptoms, resulted in more latter cases identified compared to the original clinical diagnoses. While the one-year rule is used in clinical practice, its relevance may be limited by the overlap between these disorders, with substantial group-level differences but minimal distinctions at the individual level,” says Kaasinen.

Urgent need for improved diagnostic processes

“The key conclusions of our study are the urgent need for ongoing refinement of diagnostic processes, enhanced clinical training for neurologists, more frequent use of postmortem diagnostic confirmation, and the development of widely accessible, cost-effective biomarkers,” Kaasinen summarises.

Increasing the rate of autopsies would enhance clinicians' understanding of diagnostic accuracy, particularly in cases where initial diagnoses are unclear or revised. The development of cost-effective and accessible biomarkers could improve diagnostic precision, particularly in non-specialised settings, ultimately leading to better patient care.

This retrospective study was conducted at Turku University Hospital and three regional hospitals in Finland, analysing patient records from 2006 to 2020. The study aimed to evaluate the long-term diagnostic stability of Parkinson’s disease and assess the accuracy of initial diagnoses over time in a large cohort of patients diagnosed by neurologists, with or without specialisation in movement disorders.