FMD Part 2

EPIDEMIOLOGY

The precise incidence and prevalence of FMDs are unknown, as population-based studies are unavailable. Estimates of the prevalence of FMD among adults and children with movement disorders vary between 2 to 4 percent. Women are affected more often than men.

A retrospective chart review of our centre in Toronto Canada yielded 206 patients with a diagnosis of FMD out of 7624 records, for a prevalence of 3 percent. Of note, our center receives referral from both primary care physicians and from other academic movement disorders centers. The prevalence of FMD among patients who present with dystonia and fixed, contracted joints may be even higher. As an example, one study of 41 such patients with prospective data reported that criteria for functional dystonia were fulfilled in 15 (37 percent). A review of patients assessed by a movement disorders program found that of 321 new patients, 10 percent were diagnosed with a functional movement disorder.

In most reports of adults and children with FMD, functional tremor is the most frequent type of involuntary movement, followed by functional dystonia. Among our cohort of 206 patients with FMD, the most common functional involuntary movements were tremor (33 percent), dystonia (25 percent), myoclonus (25 percent), gait disorders (11 percent), and parkinsonism (6 percent). Women comprised 77 percent of the total cohort. Although our population is culturally diverse, a formal study of transcultural differences that compared patients with FMD from the United States and Spain revealed similar frequencies of movement types, gender, anatomic distribution, and disability across ethnic groups.