Increased number of heterotopic Purkinje cells in essential tremor

Objective: Recent postmortem studies reveal degenerative changes, including Purkinje cell (PC) loss, in most brains from individuals with essential tremor (ET). Heterotopic PCs (HPCs) (ie, PC bodies displaced into the molecular layer) may be found in neurodegenerative diseases with PC loss. HPCs have been observed in ET but no quantitative case control analysis has been performed. Methods: HPCs were counted in 35 ET brains and 32 control brains (including 21 non-diseased controls and 11 diseased controls with progressive supranuclear palsy (PSP)) using a standard 20x25 mm cerebellar cortical section stained with a modified Bielscholwsky method. Results: The median number of HPCs per section was three times higher in 35 ET cases (median 3, mean±SD 3.8±3.6, range 0-14) versus 32 controls (median 1, mean±SD 1.6±1.7, range 0-5) (p=0.007). The number of HPCs was similarly low in the 21 nondiseased controls and 12 PSP brains (median 1 in each group) (p=0.04 and p=0.01 compared with ET). In ET, the number of HPCs was inversely related to the number of PCs (Spearman's rho -0.36, p=0.038) (ie, cases with more HPCs had fewer PCs). Conclusion: PC heterotopia, which occurs in cerebellar degenerative disorders, is also a feature of ET. These findings further contribute to our understanding of the postmortem changes in this common neurological disease.