AbstractThe applause sign has been previously reported to be indicative of neurodegenerative disorders, such as progressive supranuclear palsy (PSP). In order to determine the sensitivity, specificity, and positive predictive value, we tested it in patients with PSP, Parkinson's disease (PD), multiple system atrophy (MSA), corticobasal degeneration (CBD), and Huntington's disease (HD). Subjects were asked to clap three times after demonstration by the examiner. The performance was scored as follows: 3 = claps only three times; 2 = claps four times; 1 = claps 5 to 10 times; 0 = claps >10 times. The clap test was videotaped and rated. Patients with CBD, MSA, and PSP showed significant differences in clap scores compared with normal controls. The test differentiated patients with CBD from those with PD (P < 0.005) and HD (P < 0.005), but failed to discriminate patients with PSP from other parkinsonian groups. The specificity of the applause sign is 100% in distinguishing parkinsonian patients from normal subjects with the highest sensitivity in CBD patients. We concluded that the applause sign is highly specific for parkinsonian disorders but it is not a specific sign for PSP; it appears to be most sensitive for CBD. © 2008 Movement Disorder Society