Dystonia in corticobasal degeneration: a review of the literature on 404 pathologically proven cases.

Dystonia is considered one of the classical features of corticobasal degeneration and is reported in up to 83% in clinical, not pathologically confirmed, series. Here, we aimed to establish the frequency and the clinical characteristics of dystonia in CBD by reviewing the literature on 404 pathologically proven cases. Further, we aimed to identify the frequency and characteristics of dystonia in all described phenotypes with CBD pathology. Dystonia was present in only 37.5% of the 296 cases with adequate information. The majority of the cases with dystonia presented with a corticobasal syndrome, and dystonia occurred in the first 2 years from disease onset, affecting the upper limb. In cases with dystonia that presented with a "dementia" phenotype, dystonia tended to appear later in the disease course and to more affect the cervical region and the face. With regard to the distribution of the phenotypes, fifty-four percent of 374 cases presented as corticobasal syndrome, 15% as frontotemporal dementia, and 10.7% as progressive supranuclear palsy. Dystonia and myoclonus were present in about half of all cases with corticobasal syndrome, implying that these features may not be as frequent in corticobasal syndrome as are akinetic-rigid syndrome and apraxia (100% and 86.3%, respectively). Dystonia and myoclonus almost co-occurred in our analysis, suggesting a possible association. In conclusion, despite dystonia being an inclusion criterion in all sets of clinical criteria for corticobasal degeneration, this was present in only one third of the pathologically proven cases presented here. More accurate characterization of dystonia in corticobasal degeneration would be of importance for clinical diagnosis and development of treatment strategies.