Brain surgery is an option for advanced PD patients whose symptoms can no longer be managed with medications.
The best surgical candidate
is someone who:
Responds well to dopaminergic therapy
Has motor complications (‘off’ periods and dyskinesias) that are limiting factors
Is otherwise healthy and who is likely to withstand the surgery.
Advanced age is not necessarily a barrier to surgery, but some risk factors
for the surgery that decreases the likelihood of an optimal outcome are:
Impaired cognition, including forgetfulness, diminished decision-making ability, and language difficulties
Gradual loss of brain matter (brain atrophy or shrinkage)
Depending on the patient, procedure, and skill of the operating team, cognition may be mildly impaired or largely unaffected by the surgery. The most commonly reported adverse cognitive effects are reduced decision-making abilities and language impairments.
It is impossible to predict the benefit
a patient can expect from the surgery. The general thumb rule is that the maximum benefit is equal to the best response from a dose of levodopa (minus the effect on dyskinesias). Therefore, if a patient's symptoms are 50% better at the peak of a levodopa dose, the surgery is not likely to improve the patient's symptoms more than that dose. Importantly though, improvements from surgery are most dramatic during the times the patient is not experiencing the effects of medications ("off" time). Therefore, surgery may greatly increase the time when symptoms are reduced.