To conduct an individual patient data (IPD) meta-analysis of a large dataset to characterize the distribution of age of onset and determine if a gender difference exists, and determine if this differs for functional movement disorder (FMD) phenotypes. 

Functional neurological disorders are among the most prevalent conditions in outpatient neurological practice, representing 30% of referrals. FMD is a common subtype of functional neurological disorder, yet an understanding of the basic epidemiology such as age of onset and gender is not known. Also, it is not known whether different FMD phenotypes (e.g. tremor, dystonia, or weakness) are associated with different ages of onset or exhibit gender differences. A recent, large multicentre study in the UK with 698 subjects with functional seizures (psychogenic non-epileptic seizures) found a modal age of onset of 21 years and a significant difference between male and female patients, with the proportion of males affected increasing with increasing age, suggesting different risk or precipitating factors in the development of symptoms.

IPD were drawn from published literature  as well as shared by individual investigators from the MDS FMD Study Group, then amalgamated (goal > 2000 cases). Histograms were generated for the entire cohort and for each gender (primary outcomes), then the analysis was repeated for the most common sub-phenotypes (secondary outcomes).  

At the time of abstract submission, a preliminary cohort of 831 patients (240 males) demonstrated a quasi-normal distribution of age of FMD onset with a peak at 34-39 years. Data collection is ongoing and the study is anticipated to end by December 31, 2019. 

These preliminary findings suggest a 2 decade-later age of onset of FMD compared to functional seizures, indicating potentially different underlying risk, precipitating or perpetuating factors. Characterizing simple demographic data in a large cohort can uncover possible underlying neurobiological mechanisms.