-Original-

Early Stage of Progressive Supranuclear Palsy: A Neuropathological Study of 324 Consecutive Autopsy Cases

Akane Nogami^1,2, Mineo Yamazaki³, Yuko Saito⁴, Hiroyuki Hatsuta¹, Yoshio Sakiyama⁵, Masaki Takao¹, Kazumi Kimura² and Shigeo Murayama^1,6

¹Department of Neuropathology and Neurology, Tokyo Metropolitan Geriatric Hospital & Institute of Gerontology
²Department of Neurology, Nippon Medical School
³Department of Neurology, Nippon Medical School Chiba Hokusoh Hospital
⁴Department of Laboratory Medicine (Neuropathology), National Center Hospital of Neurology and Psychiatry
⁵Department of Neurology, Jichi Medical University Saitama Medical Center
⁶Department of Neurology, Tokyo Metropolitan Geriatric Hospital & Institute of Gerontology

Diagnosing clinical progressive supranuclear palsy (PSP) is challenging. We hypothesize that there are more cases of pathological PSP than have been clinically identified, but its diagnosis is challenging because the initial lesions and progression of PSP have not yet been clarified. The purpose of our study was to clarify the incidence of PSP in consecutive autopsy cases and identify pathological characteristics of early PSP. We investigated 324 consecutive autopsy patients from a general geriatric hospital (age, mean±SD=82.5±8.7 years). Paraffin sections of the midbrain were immunostained with anti 4-repeat tau antibodies (RD4). We selected cases showing RD4-positive neurofibrillary tangles and tufted astrocytes in the midbrain sections. Then, we used anti-phosphorylated tau antibody to immunostain sections from the basal ganglia, subthalamic nucleus, midbrain, pons, medulla, and cerebellum. Of the 324 patients, 35 had RD4-positive structures in the midbrain. From these 35 cases, we excluded those for which autopsies confirmed definite PSP (n=5) and cases of corticobasal degeneration (n=1), Alzheimer's disease (n=11), dementia of grain (n=10), and neurofibrillary tangles predominant forms of senile dementia (n=2), leaving 8 cases. We diagnosed these 8 cases as pure PSP-type tauopathy.
Pure PSP-type tauopathy was detected in 2.5% of the consecutive autopsy cases, and this incidence was 1.6 times greater than that of neuropathologically definite PSP. This pure PSP-type tauopathy likely indicates preclinical stages of PSP. Furthermore, the novel neuropathological finding, which we term "preclinical PSP," is unique and has not previously been reported. In order to elucidate the causes and pathological mechanisms of PSP, preclinical PSP should be investigated further.

J Nippon Med Sch 2015; 82: 266-273

Keywords
4-repeat tau, progressive supranuclear palsy, preclinical stage, tau

Correspondence to
Dr. Shigeo Murayama, Department of Neuropathology, Tokyo Metropolitan Institute of Gerontology, 35-2 Sakae-cho, Itabashi-ku, Tokyo 173-0015, Japan
smurayam@tmig.or.jp

Received, June 1, 2015
Accepted, September 28, 2015