A surgical method that uses thermoco-agulation (heat generated by electricity) or other means to destroy tissue. As a treatment for Parkinson’s disease, ablation typically targets cells in the globus pallidus that become overly active when dopaminE production declines. Destroying these cells results in a corresponding decrease in the abnormal movements that characterize Parkinson’s disease. Modern technology allows surgeons to place the lesions with great precision and few complications. Because the depletion of dopamine-producing cells in the substantia nigra continues as Parkinson’s disease progresses, ablation provides only temporary relief from symptoms.
In the usual open procedure, the patient remains awake, although sedated, during ablation to treat Parkinson’s disease. The surgeon uses a local anesthetic to numb pain-sensing nerves in the skin of the scalp and the dura (the tissue that surrounds the brain); the brain itself contains no pain-sensing nerves, so it is not necessary to anesthetize brain tissue. The surgeon then guides a fine probe, or electrode, into the region believed to be the source of tremors and other movement abnormalities. The probe delivers electronic signals that the surgeon can listen to and display on a screen (oscilloscope) to help guide the probe’s proper placement. Cells within the brain emit different and identifiable sound waves. When the probe is in the correct location, the surgeon releases small bursts of electricity or heat (or in some cases a destructive chemical like ethanol) that burn the area. The surgeon determines how much destruction is necessary by observing the changes in tremor activity. When the resulting scar heals, it permanently blocks the cells in the area and prevents them from sending signals to the muscles.
The primary risks associated with ablation are those that are possible risks with any surgery, such as reaction to the local anesthetic, bleeding, and infection. As well, there is the risk of damage to other brain tissue as the probe is inserted, which can cause problems with speech as well as localized paralysis. Often these complications lessen or go away when the damaged areas heal, although sometimes they are permanent. Because the size of the scar after healing determines the procedure’s ultimate effectiveness, the precise outcome cannot be known for seven to 10 days or more after the surgery. Swelling at the site of the ablation often causes a more pronounced response during the healing phase. As Parkinson’s disease progresses and dopamine depletion increases, tremors and other motor symptoms ultimately worsen.
An alternative to the “open” procedure is use of focused radiation (such as a gamma knife) in a “closed” procedure to cause a lesion. Though these procedures avoid any cutting of the scalp, skull, or dura, their targeting is completely based on imaging and lacks the precision of confirming the location by listening to the pattern of brain activity with a probe as is done in traditional “open” procedures. It also takes months before the exact extent of focused radiation induced lesions can be determined because irradiated neurons can take weeks to months to die.
Surgeons began using ablation to treat Parkinson’s disease and other movement disorders in the 1940s, targeting the thalamus and other structures within the brain believed to be involved in the processes of movement, as well as the globus pallidus. However, technological limitations of the time made any surgery involving the brain risky and unpredictable. Some patients recovered from ablation to enjoy relatively symptom-free lives for a decade or longer, while others developed complications such as infection and unintended movement disturbances. When the medication lEvodopa was introduced to the market in 1960, it replaced ablation as the treatment of choice for Parkinson’s disease.
Recent refinements in medical technology allow surgeons to use deep brain stimulation, which produces reversible and modifiable changes, instead of ablation. Ablation and other surgical procedures are usually options reserved for use to prolong best motor function in people who are not demented and can still walk, at least in their best medicated state, but in whom best attempts at medical therapy with anti-parkinson’s medications either lead to intolerable side effects or fail to resolve function-limiting motor fluctuations fluctuating between “off” periods when medication is no longer effective and dyskinesias. Today, ablative techniques are typically reserved for people who are poor candidates for open procedures due to underlying health conditions (for whom radiosurgical ablation is the only option), people who live in areas where they do not have access to specialists trained in the programming and management of deep brain stimulators, or possibly, people who are unlikely to comply with programming follow-up.