Functional movement disorders are best understood as a disorder of the sense of agency. The movement itself is generated by normal voluntary motor circuitry, which is why a Bereitschaftspotential precedes the jerks and why distraction abolishes them, but the internal comparison between the predicted sensory consequences of the movement and the actual feedback fails, so the movement is not experienced as self-generated. In a Bayesian framework, an abnormally strong prior belief about how the limb behaves, given very high precision by self-directed attention, overrides incoming sensory evidence and shapes the observed movement.
The imaging correlates fit this account. Hypoactivation of contralateral primary motor cortex and prefrontal regions during attempted movement is described in functional motor symptoms, and abnormal activity at the right temporoparietal junction, a region central to agency attribution and to the feeling that an action belongs to oneself, has been linked to the loss of voluntary ownership. This model explains why the symptoms are genuine and not feigned, why they are modulated by attention, and why treatments that retrain automatic movement and redirect attention away from the limb are effective.
On the ABPN blueprint this maps to the Neuroscience and mechanism of disease axis, because the item tests the pathophysiologic model rather than a bedside sign. Communicating this mechanism to patients, that the problem is a software rather than hardware fault and that it is potentially reversible, is itself therapeutic.
Incorrect Answers
- A. A structural disconnection would produce fixed deficits that do not fluctuate with attention and would not be abolished by a distracting bimanual task.
- B. Nigrostriatal degeneration produces bradykinesia, rigidity and rest tremor with abnormal dopamine transporter imaging, none of which is described here.
- C. Deliberate simulation would require evidence of consistent deception for external reward; functional disorder is defined by symptoms experienced as involuntary and is not a diagnosis of feigning.
- E. Glycine receptor antibody disease produces progressive encephalomyelitis with rigidity and myoclonus, brainstem signs and exaggerated startle, and does not remit with distraction.
Testing Pearls
- Functional movement disorders reflect impaired sense of agency with normal movement generation.
- Excessive self-directed attention gives abnormal priors high precision and shapes the symptom.
- Hypoactivation of contralateral motor and prefrontal cortex is reported in functional motor symptoms.
- Right temporoparietal junction abnormalities are linked to loss of agency attribution.
- The mechanism explains why distraction and automatic movement retraining are therapeutic.
References
- Jankovic J, Mazziotta JC, Newman NJ, Pomeroy SL, editors. Bradley and Daroff's Neurology in Clinical Practice. 8th ed. Philadelphia, PA: Elsevier; 2022. p. 2082.
- Espay AJ, Aybek S, Carson A, Edwards MJ, Goldstein LH, Hallett M, et al. Current concepts in diagnosis and treatment of functional neurological disorders. JAMA Neurol. 2018;75(9):1132-1141.
- van der Salm SM, Erro R, Cordivari C, Edwards MJ, Koelman JH, van den Ende T, et al. Propriospinal myoclonus: clinical reappraisal and review of literature. Neurology. 2014;83(20):1862-1870.
