Occurrence of the "applause sign" in patients with amyotrophic lateral sclerosis

The applause sign was originally described as a quick bedside test to discriminate progressive supranuclear palsy (PSP) (positive applause sign, PAS) from Parkinson's disease (PD) and frontotemporal dementia (FTD) (negative applause sign). However, recent research demonstrated that the test is positive not only in a subset of patients with PD and FTD, but also in other neurodegenerative diseases. We tested 22 patients with amyotrophic lateral sclerosis (ALS) together with 22 healthy sex- and age-matched controls for the occurrence of PAS. Furthermore, we performed neuropsychological testing with the EXIT-25 battery to correlate PAS with neuropsychological deficits, especially frontal lobe dysfunction. Five ALS patients (23%) and none of the controls displayed PAS (p≤0.05). The occurrence of PAS in ALS patients was not correlated with pathologic EXIT-25 scores or subtests for aberrant motor behaviour. We describe for the first time the occurrence of the applause sign in ALS and provide additional evidence that PAS is not specific for Parkinsonian disorders. Although its occurrence has been related to aberrant motor behaviour due to frontal involvement, in our study PAS did not correlate with executive dysfunction as tested by the EXIT-25 test battery, or with subtests of aberrant motor behaviour.