Torpedoes in Parkinson's disease, Alzheimer's disease, essential tremor, and control brains

Purkinje cell axonal swellings ("torpedoes"), described in several cerebellar disorders as well as essential tremor (ET), have not been quantified in common neurodegenerative conditions. The aim of this study was to quantify torpedoes Parkinson's disease (PD) and Alzheimer's disease (AD) compared with ET and control brains. Brains included 40 ET cases (34 cerebellar ET, 6 Lewy body variant of ET) and age-matched comparison brains (21 AD, 14 PD/diffuse Lewy body disease, 25 controls). Torpedoes were counted in 20 × 25 mm cerebellar cortical sections stained with Luxol Fast Blue/Hematoxylin and Eosin. The median number of torpedoes in cerebellar ET (12) was 12× higher than that of controls (1) and nearly 2.5× higher than in AD (5) or PD/DLBD (5) (all P ≤ 0.005). Furthermore, in a logistic regression model that adjusted for age and Alzheimer's-type changes, each torpedo more than doubled the odds of having cerebellar ET (Odds ratio_{cerebellar ET vs. control} = 2.57, P = 0.006), indicating that the association between increased torpedoes and cerebellar ET was independent of these Alzheimer's-type changes. Although torpedoes are increased in AD and PD, as well as cerebellar ET, the magnitude of increase in cerebellar ET is greater, and cannot be accounted for by concomitant AD or PD pathology.