Primary dystonia is dystonia without a structural brain lesion, in which dystonia (sometimes with tremor) is the only sign; its cause is genetic or unknown. Secondary dystonia is caused by something else: brain injury at birth, stroke, trauma, infection, a metabolic or degenerative disease, or medication. The newer international terms are isolated versus combined dystonia, and inherited, idiopathic or acquired cause.[1]
The difference matters most for deep brain stimulation. Primary dystonia responds best: in a prospective NEJM study of primary generalized dystonia, movement scores improved by 51% at one year.[2] Secondary dystonia caused by brain damage responds less, for example about 24% in dyskinetic cerebral palsy.[3] The important exception is tardive dystonia, which is acquired but responds as well as primary dystonia.[4]
Primary (isolated) dystonia
- Dystonia is the only movement problem, apart from tremor
- Brain MRI is normal
- Cause is genetic (for example TOR1A/DYT1, THAP1/DYT6) or unknown
- Includes most adult cervical dystonia, Meige syndrome, writer’s cramp and early-onset generalized dystonia
Secondary (acquired) dystonia
- Structural brain injury: cerebral palsy from birth injury, stroke, head trauma, encephalitis
- Medication: tardive dystonia after dopamine-blocking medications
- Metabolic and degenerative diseases: for example Wilson’s disease, or neurodegeneration with brain iron accumulation (PKAN)
- Dystonia as part of another disease, such as Parkinson’s disease, where it is often treated as part of the Parkinson’s DBS plan
DBS results: primary vs secondary dystonia
| Group | Study | Average improvement |
|---|---|---|
| Primary generalized dystonia | Prospective multicenter study, 22 patients, NEJM 2005[2] | 51% |
| Primary generalized or segmental dystonia | Sham-controlled RCT, 40 patients, NEJM 2006[5] | 15.8 vs 1.4 points |
| Cervical dystonia (mostly idiopathic) | Pooled analysis, 208 patients[6] | 58.8% |
| DYT-TOR1A (DYT1) | Meta-analysis of monogenic dystonias[7] | 68% |
| Tardive dystonia (acquired) | Meta-analysis, 117 patients[4] | 76% (BFMDRS) |
| Dyskinetic cerebral palsy (acquired) | Prospective study, Lancet Neurology 2009[3] | ≈24% |
| NBIA / PKAN (degenerative) | Meta-analysis of monogenic dystonias[7] | 27% |
Percentages refer to the movement (motor) part of the Burke-Fahn-Marsden Dystonia Rating Scale, except cervical dystonia (TWSTRS total score). Studies differ in design and follow-up, so figures are not directly comparable. Literature data, not our own case series.
Why does secondary dystonia respond less?
DBS works by modulating a brain network. When the basal ganglia or their connections are physically damaged, as after birth injury or stroke, there is less healthy circuitry for stimulation to work through. Fixed contractures and bone deformities that often accompany long-standing secondary dystonia also do not change with stimulation. A meta-regression of individual outcomes confirmed that primary dystonia does better than secondary dystonia after DBS.[8]
This does not mean DBS has no place in secondary dystonia. Even a moderate improvement can ease pain, care, sitting and feeding. The decision needs a careful, honest discussion of realistic goals.
The tardive dystonia exception
Tardive dystonia is acquired, but the brain structure is intact. It responds very well to pallidal DBS: a meta-analysis of 117 patients reported a 76% improvement on the dystonia scale and 62% on the abnormal involuntary movement scale.[4] See tardive dystonia and tardive dyskinesia.
Frequently asked questions
Which type of dystonia responds best to DBS?
Isolated (primary) dystonia, especially TOR1A (DYT1) generalized dystonia, cervical dystonia, Meige syndrome and tardive dystonia respond best.
Is DBS worth it for secondary dystonia?
It can be, but the expected benefit is smaller and less predictable. It is decided case by case, with clear goals such as less pain or easier care.
Are primary and idiopathic dystonia the same?
Not exactly. Primary dystonia includes both idiopathic dystonia (no cause found) and genetic isolated dystonia.
Sources
- Albanese A, Bhatia K, Bressman SB, et al. Phenomenology and classification of dystonia: a consensus update. Mov Disord. 2013;28(7):863–873. Source
- Vidailhet M, Vercueil L, Houeto JL, et al. Bilateral deep-brain stimulation of the globus pallidus in primary generalized dystonia. N Engl J Med. 2005;352(5):459–467. Source
- Vidailhet M, Yelnik J, Lagrange C, et al. Bilateral pallidal deep brain stimulation for the treatment of patients with dystonia-choreoathetosis cerebral palsy: a prospective pilot study. Lancet Neurol. 2009;8(8):709–717. Source
- Macerollo A, Deuschl G. Deep brain stimulation for tardive syndromes: systematic review and meta-analysis. J Neurol Sci. 2018;389:55–60. doi:10.1016/j.jns.2018.02.013 Source
- Kupsch A, Benecke R, Müller J, et al. Pallidal deep-brain stimulation in primary generalized or segmental dystonia. N Engl J Med. 2006;355(19):1978–1990. doi:10.1056/NEJMoa063618 Source
- Tsuboi T, Wong JK, Almeida L, et al. A pooled meta-analysis of GPi and STN deep brain stimulation outcomes for cervical dystonia. J Neurol. 2020;267(5):1278–1290. doi:10.1007/s00415-020-09703-9 Source
- Artusi CA, Dwivedi A, Romagnolo A, et al. Differential response to pallidal deep brain stimulation among monogenic dystonias: systematic review and meta-analysis. J Neurol Neurosurg Psychiatry. 2020;91(4):426–433. Source
- Andrews C, Aviles-Olmos I, Hariz M, Foltynie T. Which patients with dystonia benefit from deep brain stimulation? A metaregression of individual patient outcomes. J Neurol Neurosurg Psychiatry. 2010;81(12):1383–1389. Source