Progressive Supranuclear Palsy with Predominant Cerebellar Ataxia.

Progressive supranuclear palsy (PSP) is characterized by supranuclear gaze palsy, dystonic rigidity of the neck and upper trunk, frequent falls and mild cognitive impairment. Cerebellar ataxia is one of the exclusion criteria given by the National Institute of Neurological Disorders and Stroke and the Society for Progressive Supranuclear Palsy. As a result, pathologically proven PSP patients exhibiting cerebellar ataxia have often been misdiagnosed with spinocerebellar degeneration, specifically multiple system atrophy with predominant cerebellar ataxia (MSA-C). However, more recently, it has been recognized that patients with PSP can present with truncal and limb ataxia as their initial symptom and/or main manifestation. These patients can be classified as having PSP with predominant cerebellar ataxia (PSP-C), a new subtype of PSP. Since the development of this classification, patients with PSP-C have been identified primarily in Asian countries, and it has been noted that this condition is very rare in Western communities. Furthermore, the clinical features of PSP-C have been identified, enabling it to be distinguished from other subtypes of PSP and MSA-C. In this review, we describe the clinical and neuropathological features of PSP-C. The hypothesized pathophysiology of cerebellar ataxia in PSP-C is also discussed.