To determine the relevancy of the whistle-smile reflex (WSR) during the evaluation of patients with Parkinson’s disease (PD).

Described in 1943 by Frederic Hanes, the WSR, also known as Hanes’ sign, states that a healthy person, when asked to whistle, does so and smiles afterwards, while the parkinsonian patient does not smile after whistling.

We selected patients with PD and their relatives from a movement disorders outpatient clinic. They were filmed while asked to whistle, and the images were analyzed by a blinded physician who assessed if the individuals smiled or not. The absence of smiling after the whistle was considered a positive test. We stratified the smiling intensity into 4 groups. We calculated the odds ratio (OR) of the positive WSR in PD and asymptomatic patients reported with confidence intervals (CI), sensitivity (SE), specificity (SP), positive predictive value (PPV), negative predictive value (NPV), and we plot a ROC curve.

We identified 43 patients with PD (mean age=63 ±10 years, 30% female) and 44 asymptomatic relatives (average age=64 ±10 years, 51% female). The whistle-smile reflex was positive in 35/43 PD cases vs. 7/44 in the asymptomatic group (OR=23.1, 95% CI=7.6-70.5, p<0.001 SE=81.4% SP=84.1% PPV=83.3% NPV=82.2%). When stratified considering the group with the least intense smile as a positive test, the test was positive in 42/43 PD cases vs. 23/44 in the asymptomatic group (OR=38.3, 95% CI 4.8-303.7, p=0.001 SE=97.7%, SP=47.7% PPV=64.6% NPV=95.4%). ROC curve area was 0.859 (p<0.001).

The WSR can be a useful tool, adding significant data during the assessment of a patient with suspected PD.