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Overview of Dystonia
- Dystonia is a disruption in the regulation of muscle tone, usually resulting in progressive rigidity throughout the body.
- Increased tone in opposing muscles limits voluntary movement. When increased tone in opposing muscles is not symmetrical, the condition may distort posture.
- The most common form of dystonia is dystonia musculorum deformans, an inherited disorder. The specific genetic abnormality is unknown.
- The first symptoms of dystonia musculorum deformans typically begin just prior to puberty but may occur as early as age 3 or as late as young adulthood.
- When the disease begins early it usually involves the legs. Disruption of gait, or walking, may be the only symptom for some time.
- Symptom progression varies but occurs more rapidly in patients with symptoms at an early age.
- When the disease begins later in life the trunk of the body and the neck are more likely to be involved.
- Dystonia may progress to the point of almost complete immobility and death from secondary complications, usually pneumonia.
- Medical therapy is available but not uniformly effective. Nonetheless, it should be tried before considering surgical intervention.
- Deep Brain Stimulation is a surgical option.
DBS selection criteria
- Primary dystonia > Secondary dystonia
- Patients with primary dystonia due to a mutation of the DYT-1 gene respond best to DBS therapy. Those with secondary dystonias (usually due to an identifiable trauma) generally do not benefit as much but may still be considered (especially those with perinatal diffuse anoxic injury). Other brain-injury related symptoms, such as spasticity and seizures, are also relative contraindications, as these may be a greater source of disability than dystonia.
- Generalized dystonia > Focal or Segmental Dystonia
- Dystonia can be generalized (occurring throughout the body), focal (occurring in specific areas, such as cervical dystonia), or segmental (affecting two adjoining body parts). Patients with generalized dystonia respond best to DBS, although some focal dystonias (e.g., cervical dystonias) may also be considered.
- Medication refractory dystonia
- Although medical therapy is limited, to be considered for DBS therapy, patients should have failed medical therapy such as benzodiazepines, anticholinergics, Sinemet, and Botox (in the case of focal dystonia).
- Intact cognitive function
- In secondary dystonia, the greatest source of disability is often cognitive dysfunction. Because, DBS can exacerbate cognitive dysfunction, significant cognitive decline is therefore a contraindication.
- Brain MRI that is amenable to DBS surgery
- Because dystonia can be due to brain trauma, it is important to have a screening MRI to ensure that the brain is amenable to DBS surgery and that the proposed target for DBS can be identified.
- Medically suitable for surgery
- Patients should be medically suitable for surgery and have controlled blood pressure to be considered for surgery. It is preferable that patients be able to tolerate 3-6 hours of awake surgery, although the surgery can be performed asleep under certain circumstances.
- Realistic expectations and interest
- Patients must realize that DBS therapy is not a "cure" but symptomatic therapy. In most cases, patients achieve their best response between 3 and 12 months after implantation.
- Results of surgery can be dramatic in carefully selected patients. Some improvement occurs in 50 percent to 70 percent of patients. Improvements may not be apparent for several weeks or months.