The goals of brain surgery for persons with dystonia are to decrease muscle spasms, increase mobility and function, and improve pain.
There are currently two categories of brain surgery for dystonia: lesioning procedures, which involve selective destruction of targeted, abnormal brain tissue, and deep brain stimulation(DBS), which mimics the effects of lesioning by manipulating selective brain areas with non-destructive electrical pulses.
Although risks exist, case studies have shown that both lesioning procedures and DBS can result in marked improvement of dystonia with minimal complications. Some patients are able to decrease or altogether stop drug therapy following surgery.
Dystonia most often originates in a part of the brain called the basal ganglia which are involved in the coordination and control of muscle movements. The basal ganglia are a group of structures that include the globus pallidus (also called the pallidum), the thalamus, and the subthalamic nucleus. Lesioning procedures for dystonia usually target the globus pallidus or the thalamus; deep brain stimulation usually targets the globus pallidus or subthalamic nucleus. The globus pallidus is responsible for the output of messages from the basal ganglia. The recipient of this output is the thalamus. The subthalamic nucleus is a tiny structure located directly beneath the thalamus and is connected to the globus pallidus.
Different parts of the brain work together to help the body accomplish a specific task, such as tapping the foot. The parts of the brain communicate via circuits or pathways of individual brain cells that transmit chemical messages from one to the other. In an individual with dystonia, the circuits that facilitate the movement of the foot are disrupted by abnormal activity. The goal of brain surgery is to free up the circuits so that the brain and body may accomplish the intended function—in this case, moving the foot.
Brain surgery may be performed unilaterally (on one side of the brain) or bilaterally (on both sides). The effects of surgery occur on the side of the body opposite to the surgical site.
To date, most persons who have undergone brain surgery for dystonia were treated for generalized dystonia. However, individuals who may be eligible for brain surgery include persons with focal, segmental, or generalized dystonia with significant, disabling symptoms that do not respond satisfractorily to other therapies. Adults as well as children with primary and secondary dystonia may be eligible.
Based on the limited available data, different categories of patients may respond differently to brain surgery. Although cases of both secondary dystonias (including tardive dystonia) and focal dystonias may be eligible, it appears as though persons with DYT-1 generalized dystonia are the best candidates for brain surgery—either lesioning or DBS. Studies have shown as much as 60-90% improvement in DYT-1 patients treated with lesioning or DBS. Patients with secondary hemidystonia may be eligible for brain surgery, though they may not benefit as much as those with DYT-1 dystonia. Researchers are examining the possibility that persons with secondary dystonia may get greater benefit from lesioning or DBS to the thalamus rather than the globus pallidus.
There is limited data about the long-term effects of each approach. Brain surgery for dystonia is an evolving science, and investigators are continually collecting information.