A Quantitative Study of Empty Baskets in Essential Tremor and Other Motor Neurodegenerative Diseases

The underlying biology of essential tremor (ET) is poorly understood. Purkinje cell (PC) loss has been observed in some studies, although this finding remains somewhat controversial. Basket cells are interneurons whose axonal collaterals form a plexus around PC soma. When there is PC loss, this basket plexus appears empty. We used dual immunohistochemical staining for calbindin D28k and glutamic acid decarboxylase to quantify "empty baskets" as an indirect and alternative method of detecting PC loss. Microscopic analyses on 127 brains included ET and a spectrum of motor neurodegenerative diseases (50 ET, 27 spinocerebellar ataxias [SCAs], 25 Parkinson disease, 25 controls). The median percentage of empty baskets in ET patients was 1.5 times higher than controls (48.8% vs 33.5%, p < 0.001) but lower in ET than in SCA1 (59.7%, p = 0.011), SCA2 (77.5%, p = 0.003), and SCA6 (87.0%, p < 0.001). PC loss is not a feature of SCA3, and the median percentage of empty baskets (30.1%) was similar to controls (p = 0.303). These data provide support for PC loss in ET and are consistent with the notion that ET could represent a mild form of cerebellar degeneration with an intermediate degree of PC loss.