Ballooned neurons in progressive supranuclear palsy are usually due to concurrent argyrophilic grain disease

Progressive supranuclear palsy (PSP) is a sporadic multisystem neurodegenerative disorder that is one of the major causes of parkinsonism, which shares common biochemical and genetic features with corticobasal degeneration (CBD). Ballooned neurons (BN) are one of the histopathologic hallmarks of CBD and their presence is a neuropathologic feature that helps differentiate PSP from CBD, since BN are uncommon in PSP. There are, however, several reports in the literature of BN in PSP. BN are also a consistent finding in argyrophilic grain disease (AGD), where they are relatively confined to limbic structures, in particular the amygdala. Since AGD has been found with increased frequency in PSP, it is possible that cases of PSP with BN may represent co-existing AGD. In the present study, we investigated this possibility by studying the distribution and the density of BN with αB-crystallin immunostaining in 20 cases of PSP, including equal numbers of cases with and without co-existing AGD. In PSP cases with concurrent AGD, BN were consistently found in limbic areas, but in pure PSP cases, BN were rare, supporting the hypothesis that concurrent AGD may account for most cases of PSP with BN.