Functional and Stereotactic Neurosurgery
Core concepts
Understand the basal ganglia-thalamocortical circuitry relevant to Parkinson disease and the rationale for deep brain stimulation (DBS) targets: subthalamic nucleus (STN) and globus pallidus interna (GPi). Know patient selection (levodopa-responsive, cognitively intact) and DBS programming basics (monopolar vs bipolar, amplitude, frequency, pulse width). Understand stereotactic principles, frame-based vs frameless techniques, and targeting accuracy. Know indications for other functional procedures: thalamotomy/pallidotomy, radiosurgery for tremor, and intrathecal baclofen for spasticity. Understand the pathophysiology of essential tremor and dystonia. Recognize the role of lesioning vs stimulation and the risks (hemorrhage, infection, cognitive/behavioral effects).
Traps
A common trap is selecting a DBS candidate who is not levodopa-responsive or has significant cognitive impairment. Another is misattributing stimulation-induced dysarthria or paresthesias to disease progression rather than programming. Questions may test that GPi is preferred when dyskinesia or dystonia is prominent, while STN allows medication reduction. Watch for confusion between essential tremor (postural/action) and Parkinson tremor (resting).
Worked rule of thumb
DBS candidacy: levodopa-responsive symptoms, no significant cognitive impairment, and realistic goals. For a patient with prominent dyskinesias, GPi is often favored; for medication reduction, STN is often favored. Stimulation side effects usually improve with reprogramming, not necessarily reoperation.