Epidemiology

The epidemiology of functional neurologic disorders (FND) is complex and has been hampered over the years by a lack of clear definition, with previous definitions struggling with an uneasy mix of both physical and psychologic components. The recent changes in DSM-5 to a definition based on positive identification of physical symptoms which are incongruent and inconsistent with neurologic disease and the lack of need for any associated psychopathology represent a significant step forward in clarifying the disorder. On this basis, FND account for approximately 6% of neurology outpatient contacts and putative community incidence rates of 4-12 per 100 000 per annum. Comorbid neurologic disease occurs in around 10% of cases. The diagnosis is reliable, with revision rates less than 5%. Of note, this revision rate was consistent prior to the widespread utilization of computed tomography and magnetic resonance imaging. FND symptoms are disabling and associated with significant distress. They are more common in women and have a peak incidence between the ages of 35 and 50; however the presentation is common in men and throughout the lifespan. The issues surrounding case definition, ascertainment, misdiagnosis, and risk factors are discussed in detail.