Experimental evidence for a robust, transdiagnostic marker in functional disorders: Erroneous sensorimotor processing in functional dizziness and functional movement disorder

Objective: Recent neuroscientific models suggest that functional bodily symptoms can be attributed to perceptual dysregulation in the central nervous system. Evidence for this hypothesis comes from patients with functional dizziness, who exhibit marked sensorimotor processing deficits during eye-head movement planning and execution. Similar findings in eye-head movement planning in patients with irritable bowel syndrome confirmed that these sensorimotor processing deficits represent a shared, transdiagnostic mechanism. We now examine whether erroneous sensorimotor processing is also at play in functional movement disorder. Methods: We measured head movements of 10 patients with functional movement disorder (F44.4, ICD-10), 10 patients with functional dizziness (F45.8, ICD-10), and (respectively) 10 healthy controls during an eye-head experiment, where participants performed large gaze shifts under normal, increased, and again normal head moment of inertia. Head oscillations at the end of the gaze shift served as a well-established marker for sensorimotor processing problems. We calculated Bayesian statistics for comparison. Results: Patients with functional movement disorder (Bayes Factor (BF)₁₀ = 5.36, BF_incl = 11.16; substantial to strong evidence) as well as patients with functional dizziness (BF₁₀ = 2.27, BF_incl = 3.56; anecdotal to substantial evidence) showed increased head oscillations compared to healthy controls, indicating marked deficits in planning and executing movement. Conclusion: We replicate earlier experimental findings on erroneous sensorimotor processing in patients with functional dizziness, and show that patients with functional movement disorder show a similar impairment of sensorimotor processing during large gaze shifts. This provides an objectively measurable, transdiagnostic marker for functional disorders, highlighting important implications for diagnosis, treatment, and de-stigmatization.