The applause sign in cortical and cortical-subcortical dementia.

The "applause sign" is a motor perseveration described in focal and neurodegenerative disorders and characterized by fronto-subcortical dysfunction. Most previous formal investigations focused on Parkinson's disease or progressive supranuclear palsy. We assessed the prevalence of the applause sign in patients affected by Alzheimer's disease (AD), Lewy body dementia (LBD), corticobasal syndrome (CBS), and posterior cortical atrophy (PCA), with the aim to verify its contribution to the differential diagnosis. We enrolled 20 patients with AD, 20 with LBD, 16 with CBS, and ten with PCA, and 30 healthy controls. The three clap test (TCT) was used to elicit the applause sign, and was scored by raters blinded to the diagnosis. Correlation with motor (extrapyramidal) and cognitive measures was also performed. A maximum 40 % prevalence of a positive applause sign was found in the two parkinsonian syndromes, which could be discriminated from the two cortical groups with a positive predictive value of 82 % and a negative predictive value of 55 %. According to our findings, a diagnosis of LBD or CBS, rather than of AD or PCA, is highly probable in the presence of an abnormal TCP, but cannot be ruled out based on a negative result. No relevant correlates emerged that could clarify the origin and nature of the applause sign.