Changing nosology, unknown epidemiology: What do we know about functional neurological disorders in the community?

To estimate the epidemiology of functional neurological disorders (FND) in the general population through a systematic literature review and to assess the quality of the included studies.

FND are characterized by motor and/or sensory symptoms that relate to functional rather than structural abnormalities. Although these disorders are common in neurology, their epidemiology is not well documented.

Following the Preferred Reporting Items for Systematic Reviews and Meta-analyses guidelines, we searched PubMed and Embase for articles reporting on the incidence or prevalence of FND in adults, published in French or English between 1972 and 2022. We used The Joanna Briggs Institute Prevalence Critical Appraisal Tool to assess the quality of the studies. This study was registered under the ID CRD42023434331 in the PROSPERO database.

Out of 4260 screened articles, 27 were included, primarily from India, the US, and Europe. The prevalence estimates for hysteria, conversion disorders or FND ranged from 37.2 to 6900 per 100,000, with an incidence ranging from 10.7 to 186. Functional dissociative seizures had a prevalence of 23.8 to 890 and an incidence of 0.91 to 4.9. Functional motor disorders had an incidence of 3.9 to 5.0. Most cases involved young women. Only eight studies were rated as high quality. Overall, the rapidly changing nosology and diagnostic criteria complicate the interpretations of existing data.

Our findings highlight the urgent need for large-scale, rigorous studies targeting the multiple forms of FND to obtain reliable epidemiological data necessary to develop an adequate health policy for FND.