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The nature of the applause sign, that is, the tendency to perform an automatic series of claps in response to the instructions to clap three times, has not been fully understood.1 The behavioural variant of frontotemporal dementia (bvFTD) is a good model to assess the influence of the frontal lobe dysfunction in generating the applause sign. Applause sign in FTD is a debated issue: its frequency ranges from 0% to 60% in different case series.1 ,2 BvFTD entails two distinct phenotypical patterns depending on the behavioural changes the patients show and on the distribution of atrophy3: the apathetic bvFTD, characterised by loss of initiative and volition, inertia and apathy, and the disinhibited bvFTD characterised by hyperactivity, verbal and motor disinhibition.
A third rare variant has been reported as the ‘stereotypical variant’ which is mainly characterised by aberrant motor behaviour with perseverations, mannerisms and rituals.3 Rarely repetitive behaviour can be found in the apathetic variant. By contrast, complex repetitive behavioural routines are often present in the disinhibited variant suggesting that the disinhibited and stereotypical variants tend to overlap.3 Although the atrophy spreads across the frontotemporal lobes, the distribution of atrophy tends to be more pronounced in the dorsolateral prefrontal cortex in apathetic bvFTD, in the orbitofrontal frontal cortex in the disinhibited bvFTD,4 and in the frontostriatal cortex in the stereotypical bvFTD, respectively.3
The present study aimed to verify the hypothesis that the applause sign arises from an aberrant motor behaviour. Accordingly, it is expected to be a frequent sign of the disinhibited and stereotypical variants. The apathetic variant, characterised …