The pathogenesis of essential tremor is poorly understood. Historically, the inferior olivary nucleus has been hypothesized to play an important role in the generation of tremor in essential tremor, yet a detailed, controlled, anatomic-pathological study of that brain region has yet to be conducted.

A detailed postmortem study was undertaken of the microscopic changes in the inferior olivary nucleus of 14 essential tremor cases vs. 15 age-matched controls at the Essential Tremor Centralized Brain Repository. A series of metrics was used to quantify microscopic neuronal and glial changes in the inferior olivary nucleus and its input and output tracts. Olivary linear neuronal density was also assessed.

Cases and controls did not differ from one another with respect to any of the assessed metrics (p values ranged from 0.23 – 1.0). Olivary linear neuronal density was also similar in cases and controls (p = 0.62). Paddle-shaped neurons, a morphologic shape change in olivary neurons, which to our knowledge have not been previously recognized, occurred to an equal degree in ET cases and controls (p = 0.89), and correlated with several markers of neuronal loss and gliosis.

A systematic postmortem study of the microscopic changes in the inferior olivary nucleus did not detect any differences between cases and controls. These data, along with positron emission tomography data, which have failed to identify any metabolic abnormality of the olive, indicate that if the olive is involved in essential tremor, there is no clearly identifiable structural or metabolic correlate.