Essential Tremor Followed by Progressive Supranuclear Palsy: Postmortem Reports of 11 Patients

For many years, clinicians have commented on the development of signs of parkinsonism among their essential tremor (ET) patients, but the links between ET and parkinsonism are not well understood. We report 11 (12.4%) of 89 ET patients who were prospectively collected at the Essential Tremor Centralized Brain Repository during the course of its first 9 years. All patients had long-standing ET (median duration, 38 years); there was a 5- to 49-year latency from the onset of ET to the development of either parkinsonism or dementia. Despite the presence of parkinsonism or dementia during life, none had been diagnosed clinically with progressive supranuclear palsy (PSP). All 11 received the postmortem diagnosis of PSP. The prevalence of PSP in this ET sample (12.4%) is clearly larger than the population prevalence of PSP (0.001%-0.0065%). It is also 2 to 5 times the proportion of normal cases with incidental PSP in 2 previous autopsy series. This case series raises the questions of an association between ET and PSP, whether ET patients are at an increased risk of developing PSP, and what the proportion of ET patients who develop presumed Parkinson disease or Alzheimer disease in life actually have PSP (i.e. ET + PSP).