Fixed dystonia is a characteristic functional presentation: a young, usually female patient develops a sustained posture, most often a clenched fist or an inverted plantar-flexed foot, shortly after a peripheral injury that is often trivial. The posture is fixed from the start rather than emerging as a mobile action-induced dystonia, it is frequently painful, and it is very commonly accompanied by the vasomotor, sudomotor and allodynic features of complex regional pain syndrome type 1. The largest published series of 103 patients established this phenotype and its association with pain and with young female sex.
The distinction from idiopathic dystonia is clinical. Organic focal dystonia begins as a mobile, task-specific or action-induced posture, often improves with a sensory trick, and usually spares the limb at rest early on; fixed dystonia does the opposite. Neurophysiologic studies show overlapping abnormalities in cortical excitability and sensorimotor integration in both fixed dystonia and organic dystonia, which is why physiology cannot settle the question at the bedside. Contemporary reviews argue that complex regional pain syndrome and functional neurological disorder share mechanisms of abnormal predictions, attention and disuse, and should be managed together rather than as rival explanations.
Fixed dystonia is a fellowship-level movement disorders topic, so this item sits at the Subspecialty level of RITE content. Examination under sedation or general anaesthesia can demonstrate that the posture resolves, which supports the diagnosis and may guide rehabilitation, although it has no lasting therapeutic effect on its own.
Incorrect Answers
- B. Writer cramp is task-specific, is absent at rest, typically improves with a sensory trick, and is not painful or associated with vasomotor change.
- C. Dopa-responsive dystonia begins in childhood with diurnal worsening and lower limb onset, and resolves dramatically on low-dose levodopa.
- D. Tardive dystonia requires exposure to a dopamine receptor blocking drug and usually affects the neck, trunk or face with retrocollis and opisthotonic posturing.
- E. Wilson disease presents with additional features such as Kayser-Fleischer rings, dysarthria, tremor, psychiatric change and abnormal copper studies.
Testing Pearls
- Fixed dystonia typically begins after a minor peripheral injury in a young woman.
- The clenched fist and the inverted plantar-flexed foot are the classic postures.
- Complex regional pain syndrome type 1 features accompany fixed dystonia in most patients.
- Organic focal dystonia is mobile, action-induced and often eased by a sensory trick.
- Resolution of the posture under sedation supports the diagnosis but is not curative.
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. 2083.
- Schrag A, Trimble M, Quinn N, Bhatia K. The syndrome of fixed dystonia: an evaluation of 103 patients. Brain. 2004;127(Pt 10):2360-2372.
- Popkirov S, Hoeritzauer I, Colvin L, Carson AJ, Stone J. Complex regional pain syndrome and functional neurological disorders - time for reconciliation. J Neurol Neurosurg Psychiatry. 2019;90(5):608-614.
