Applause sign

Applause sign can be demonstrated by asking patients to rapidly clap three times after  demonstration by the examiner. 

A positive applause sign occurs when patients clap more  than three times. The applause sign is very sensitive to parkinsonian syndromes,  including multiple system atrophy, progressive supranuclear palsy, and corticobasal  degeneration, but it is not specific. Occasionally, the applause sign can also occur in  Parkinson disease and Huntington disease patients. The mechanism might be due to  frontal and basal ganglia dysfunction. 

Fonts. AAN 2009; Neurology 2005