How strong is the link between trauma and FND—any better estimates?

The short version: the evidence for a trauma-FND link is strong in association but weak in causation, and the numbers are not as precise as the question hopes for.

The best estimate comes from the 25-center Italian study cited in the previous answer: about 79% of 410 patients with functional motor disorder reported a major life event or trauma, and 59% reported abuse [1]. A Turkish pediatric study of 35 children with FND found significantly higher childhood trauma scores (CTQ mean 40.1 vs 31.6 in controls) and more recent stressors (66% vs 19%) [4]. But these are case-control designs, not prospective cohorts. They cannot tell you what fraction of traumatized people develop FND, only that FND patients report more trauma than controls.

The dissociation studies add a layer. A 1997 longitudinal study of 77 sexually abused girls found elevated dissociation scores that persisted across multiple timepoints [3]. A 2019 Omani study of 84 people with dissociative possession states found that the more severe subtype had worse executive function and higher trauma rates [2]. These suggest trauma shapes the nervous system in ways that could predispose to FND, but they do not measure the transition from trauma to FND directly.

What is missing is the prospective design. No study tracked a large cohort of traumatized children into adulthood to see what fraction developed FND. No study compared FND patients to trauma-exposed controls who did not develop FND, which would isolate what makes the difference. The association is real but the effect size is not pinned down. The 79% figure from the Italian study is the closest to an estimate, but it comes from a single-center sample with no replication.

My call: trauma is a strong risk factor for FND, but the evidence cannot give a precise risk estimate because the right studies have never been done. Confidence: moderate for the association, low for any specific number.