The criteria for patient selection for DBS of the GPi and STN for PD are similar. The ideal candidate is a patient with idiopathic levodopa responsive PD who has medication resistant motor fluctuations and / or dyskinesia. It is recommended that patients undergo a levodopa challenge. Generally, patients arrive at the clinic 12 hours after not taking any antiparkinsonian medications at which time they are evaluated with a complete UPDRS and other site-specific measures. After these evaluations either the regular dose of antiparkinsonian medication or at some sites a dose of levodopa 150% of the usual dose (without any other antiparkinsonian medication) is usually given and evaluations are repeated after the patient has reached the best medication on state. Usually, a 30% or greater improvement in UPDRS motor scores between the medication off and on conditions is required to recommend surgery.
Patients older than 75 years are generally not considered candidates as they may have difficulty in tolerating the procedure and the programming. Patients should have been tried on combinations of different antiparkinsonian medications and evaluated by a movement disorder specialist, if possible, before being recommended for surgery. Patients with disabling medication resistant tremor or an inability to tolerate antiparkinsonian medications may also be candidates for STN or GPi DBS. There should be no evidence of dementia or significant cognitive, psychiatric or behavioral abnormalities as these can worsen after surgery. To rule these out, patients should undergo detailed neuropsychological testing. There should be no significant abnormalities on neuroimaging and no other medical conditions that might increase surgical risk. Finally, the patient should have an adequate support network and be able to attend multiple visits to the surgical site for programming.
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