Diagnosing functional neurological disorder: seeing the whole picture.

Functional neurological disorder (FND) is a complex neuropsychiatric syndrome with many phenotypes that are commonly encountered in clinical practice. Despite the heterogeneity of FND, the rate of misidentification is consistently low. For the more common motor subtypes, there are clear positive clinical, electrophysiological, and rarely imaging criteria that can establish the diagnosis in the traditional sense. For nonmotor subtypes, the characterization may be less clear. Here, we argue that the current diagnostic criteria are not reflective of the current shared neuropsychiatric understanding of FND, and, as a result, provide an incomplete picture of the diagnosis. We propose a three-step diagnostic triad for FND, in which the traditional neurological diagnosis is only the first element. Other steps include psychiatric/psychological formulation, integration, and follow-up. We advocate that this diagnostic approach should be the shared responsibility of neurology and mental health professionals. Finally, a research agenda is proposed to address the missing factors in the field.