A surgical procedure that creates a lesion (scar) in the thalamus to disrupt the nerve signals between the brain and the muscles. The thalamus regulates neuron communication between the cerebral cortex, which initiates voluntary movement, and the structures of the brain that participate in controlling and coordinating voluntary movement (primarily the basal ganglia, brainstem, and cerebellum). Thalamotomy is effective for reducing tremors in some people with Parkinson’s disease but does not usually have a significant effect on other symptoms such as bradyki-nesia and akinesia; pallidotomy, a similar lesioning procedure that targets the pallidus rather than the thalamus, is more effective for reducing these symptoms.
Neurosurgeons first used thalamotomy in the 1950s, before the computer and imaging technology used today to assure precision in placement of the lesion was available. In its early years, thalamotomy had a high rate of complications that often included other neuromuscular disturbances such as dyskinesias (involuntary, abnormal movements) and even paralysis. When levodopa debuted in 1967 as a viable dopamine replacement therapy for Parkinson’s disease, it supplanted the riskier surgical treatments as the treatment of first choice.
As computer technology has made great precision in placing lesions now possible, however, thalamotomy has again become a treatment option for a select few people with Parkinson’s; the greatest success in long-term symptom relief occurs in those who have tremor-dominant Parkinson’s affecting only one side of the body. Thalamotomy also is an effective treatment alternative for essential tremor, another neuromuscular disorder that produces tremors. The thalamus is a paired structure, with one on either side of the brain. Bilateral procedures are avoided since they have a high risk of causing problems with swallowing (dysphagia), speaking (dysarthria), or thinking. Unilateral procedures are safer, but they carry some risk of causing numbness, gait problems, dysarthria, balance problems, or thinking changes. Neurosurgeons typically target a small area of the thalamus called the ventral intermediate nucleus (VIM), the cells of which become overly active in Parkinson’s disease targeting the thalamus that is opposite the side of the body experiencing the more severe tremors. This is done because nerve structures cross when they leave the brainstem, controlling activity on the opposite side of the body.
Thalamotomy is generally a treatment that becomes a reasonable option only when medications do not control symptoms. As in all neuro-surgery, thalamotomy carries risks of infection, bleeding, and damage to other parts of the brain. It is not an effective alternative for people who have Parkinson’s plus syndromes or for those who are doing well with anti-parkinson’s medications. People who have bilateral tremors (tremors equally affecting both sides of the body) may not receive adequate relief as tremors continue on the nonle-sioned side.
Thalamotomy generally is performed as inpa-tient surgery; the person spends the nights before and after the procedure in the hospital. The day before the surgery, the neurosurgeon affixes the stereotaxic halo, a device attached to the skull that allows the precision of computer-assisted placement of the microelectrodes that deliver the ablative lesion. magnetic resonance imaging (MRI) determines the location for placing the lesion, and the halo allows the computer to guide electrode induction and placement. Although the ablation can be performed by radiosurgery, which requires no sedation, most procedures are open procedures that use thermocoagulation to destroy the tissue. During surgery the person receives mild sedation to relieve anxiety but remains awake to respond to directions from the neurosurgeon, to allow for normal neuronal activity so that microelectrode recording patterns may be used to confirm the location of tremor synchronous firing thalamic neurons, and to assess the effect of the lesion, which is immediate. The person’s participation helps to ensure that the lesion is in the correct place and to minimize inadvertent damage to adjacent brain structures.
The healing process takes about eight weeks, during which the lesion first swells and then recedes into a permanent scar. During the swelling phase the person sometimes experiences dyskine-sias and even dystonia (extreme rigidity that often causes unnatural and uncomfortable positions). As healing progresses, these problems usually abate. Tremors often, but not always, completely disappear when healing of the lesion is complete. Rigidity usually improves as well, as both symptoms result from excessive stimulation of muscle tissues. The person still needs anti-Parkinson’s medications to relieve other neuromuscular symptoms such as bradykinesia, although often dosages can be reduced significantly. Although the effects of thala-motomy are permanent, tremors generally return within 18 months to three years as the surgery cannot stop the progression of the Parkinson’s.