Emerging concepts on bradykinesia in non-parkinsonian conditions

Bradykinesia is one of the cardinal motor symptoms of Parkinson's disease. However, clinical and experimental studies indicate that bradykinesia may also be observed in various neurological diseases not primarily characterized by parkinsonism. These conditions include hyperkinetic movement disorders, such as dystonia, chorea, and essential tremor. Bradykinesia may also be observed in patients with neurological conditions that are not seen as "movement disorders", including those characterized by the involvement of the cerebellum and corticospinal system, dementia, multiple sclerosis, or psychiatric disorders. We provide an updated overview of bradykinesia in non-parkinsonian conditions and discuss the major findings of clinical reports and experimental studies. From a pathophysiological standpoint, bradykinesia in neurological conditions not primarily characterized by parkinsonism may be explained by brain network dysfunction. In addition to the pathophysiological implications, the present paper highlights important terminological issues and the need for a new, more accurate, and more widely-used definition of bradykinesia in the context of movement disorders and other neurological conditions.