Oral applause sign in progressive supranuclear palsy.

The applause sign (AS) is a recognized phenomenon observed in progressive supranuclear palsy (PSP) and other neurological conditions where individuals produce over three claps following a request to clap only thrice after a demonstration. In this study, we introduced a novel linguistic phenomenon termed the oral applause sign (OAS) associated with the AS. The OAS is characterized by increased repetition counts of Japanese repetitive onomatopoeic words, such as uttering "pata-pata-pata" instead of the expected "pata-pata." We identified this phenomenon in a patient with PSP exhibiting the AS and mild apraxia of speech. In addition, we developed the three-"pata" test, instructing the patient to say "pata" only thrice after demonstration without any semantic context, and reproduced the phenomenon of the additional increase of "pata" verbalization. The core feature of OAS is an inability to limit the count when repeating a small number of syllables continuously, similar to the inability to stop clapping. The shared features between the OAS and AS suggest potential overlapping mechanisms involving the dysfunction of the frontal lobe and subcortical structures and possibly, apraxia of speech. Considering that the OAS is triggered purely by repetition and unlikely to be affected by semantic content, it might be observable in Japanese and other languages. Longitudinal studies with larger cohorts across various neurodegenerative diseases and languages may elucidate the underlying mechanisms of the OAS and confirm its specificity to PSP, thus improving the generalizability and clinical relevance of the findings.