The selfie sign in the diagnosis of functional tremor.

Functional tremor (FT) is the most common phenotype of functional movement disorders (FMD). Its diagnosis can often be challenging. While positive signs such as tremor variability, distractibility, and entrainment support a diagnosis of FT, these diagnostic clues may not always be present and can be challenging to assess. In this case series, we identify another examination technique which could be of value when assessing FT. In our Movement Disorders clinic, charts were retrospectively reviewed for relevant clinical information. Video examinations were conducted. Obtained videos were either synchronous, via the use of screen recording software during telehealth visits or asynchronous, from self-recorded home videos. In both settings, patients were instructed to self-record their tremor using their phone cameras. Three patients with FT or comorbid FT were identified as demonstrating a unique examination sign. Videos showed an improvement or suppression of the tremor when the phone was held by the affected hand. When compared to a patient with tremor-dominant Parkinson's disease serving as a control, this "selfie sign" was not observed. These observations are preliminary and larger studies are needed to confirm the usefulness of the selfie sign in diagnosing FT. Patient-recorded videos of their tremor can be a convenient and practical way of evaluating suspected FT, especially when paroxysmal or variable symptoms limit the usefulness of classic signs often assessed in the clinic.