A Critical Appraisal of the Whack-a-Mole and Swivel Chair Signs in the Diagnosis of Functional Movement Disorders

Background: The demonstration of positive signs during neurological examination is a cornerstone of the diagnosis of functional movement disorders, however, the available data supporting the diagnostic value of some of these signs is limited. Objectives: To determine the diagnostic value (sensitivity and specificity) of the “whack-a-mole” (WAM) and “swivel chair” (SC) tests in patients with functional movement disorders (FMD). Methods: We enrolled patients with functional and organic movements in the WAM test if they exhibited tremor, dystonia, myoclonus, chorea, or tics. For the SC test, patients with a gait disorder as their primary impairment were recruited. Two blinded movement disorder specialists rated the presence of these signs in edited videos. Results: Inclusion criteria were met by 42 patients with FMD and 65 patients with organic movement disorders. Both tests demonstrated high specificity (means, 78% and 96%), but their sensitivity was low (means, 52% and 37%). Interobserver agreement for the WAM sign was 0.77 in the FMD group, against 0.28 in patients with organic movement disorders, whereas Movement Disorders Clinical Practice for Review Only for the SC sign was 0.69 in both groups. Conclusions: The present study indicates that physicians must be cautious in the application and interpretation of these clinical signs in the diagnosis of functional movement disorders, and they should be carefully considered and used as necessary.