Prion diseases reported in the "Annual of the Pathological Autopsy Cases in Japan".

Background: For surveillance projects to be successful, it is important to accurately diagnose all patients, without overlooking any cases. Here, we investigated the present clinical diagnostic accuracy for prion diseases in Japan.

Methods: We analyzed volumes of the "Annual of the Pathological Autopsy Cases in Japan", which reported details on 130,105 autopsies conducted from 2007 to 2016 throughout Japan.

Results: The clinical diagnosis of patients with prion disease had a specificity of 91.3% and a sensitivity of 96.3%. The autopsy rates were estimated as 17.8% for patients with clinically suspected prion disease and as 1.8% for the entire population.

Conclusions: Despite the good accuracy of clinical diagnoses of prion diseases, a calculated 78.4 patients with prion disease were expected to have gone undiagnosed during the 10-year study period. However, autopsy is estimated to reveal a maximum of only 13.8 of these clinically undiagnosed patients because of the low autopsy rate. The overall autopsy rate, irrespective of any specific disorder, must increase for effective surveillance projects of disease incidence to be conducted.