Editors' Note: Shoulder-Tap Test for Functional Gait Disorders: A Sign of Abnormal Anticipatory Behavior

Dr. Coebergh and colleagues described exaggerated postural responses in 25 patients with functional gait disorders, following a sudden shoulder tap applied by an examiner from behind the patient. In response, Dr. Geroin et al. comment that in their own population of patients with functional neurologic disorders, a light touch on the shoulders seemed to provide fewer false-positive results, given that a sudden tap could evoke exaggerated responses in patients with disorders such as hyperekplexia or stiff-person syndrome. They also note that it is not necessary to see an intact response to a retropulsion test in patients with functional gait disorders to flag their shoulder-test response as incongruent. Responding to these comments, Dr. Coebergh agrees that a light touch would likely suffice, noting that the actual contact with the shoulders in the described shoulder-tap test is light, while also highlighting work being performed by their group in identifying sensory thresholds of force at which incongruent postural responses occur in such patients. To illustrate the potential value of observing incongruity in responses to shoulder-tap vs retropulsive stimuli in patients with functional gait disorder, Dr. Coebergh highlights a case of a patient with stiff-person syndrome misdiagnosed as a functional neurologic disorder, in whom such incongruity was not observed. This exchange demonstrates the enduring value of systematic clinical examinations and observations in improving the diagnosis of functional neurologic disorders.