Parkinson's Disease

When the response to medication wears thin

Parkinson's disease is a progressive condition causing tremor, rigidity (stiffness), slowness of movement, and later problems with balance, due to the loss of dopamine-producing brain cells. Levodopa and related medications work well at first. Over time, however, the response often becomes uneven: the benefit wears off between doses (motor fluctuations, or "on-off"), and higher doses can trigger extra involuntary movements (dyskinesia). It is at this stage that surgery is considered.

For motor fluctuations and dyskinesia, in the right candidate

Surgery is for people whose Parkinson's still responds to levodopa but whose response has become unpredictable, with disabling motor fluctuations, dyskinesia, or tremor that medication no longer controls smoothly. A key predictor of success is how well the symptoms respond to levodopa: a strong response predicts a strong surgical result. Evaluation also screens out atypical forms of parkinsonism, which respond poorly, and significant cognitive impairment.

Surgical options

• Deep brain stimulation (DBS)
  Adjustable electrodes placed in the subthalamic nucleus (STN) or globus pallidus (GPi) deliver stimulation that smooths out the motor fluctuations, reduces dyskinesia, and improves tremor, rigidity, and slowness. STN stimulation often allows a meaningful reduction in medication. The benefit is durable, and because nothing is destroyed, settings can be tuned, reduced, or switched off. Published series show marked reduction in dyskinesia and improvement across the motor symptoms.
• VIM target for tremor-predominant disease
  When tremor is the dominant and most disabling symptom, the VIM nucleus of the thalamus is targeted, by stimulation or by a lesion, which is particularly effective for tremor.
• MR-guided focused ultrasound (MRgFUS)
  Hundreds of ultrasound beams converge to make a precise lesion in the thalamus or globus pallidus with no incision and no implant, under real-time MRI thermometry. An option for tremor and for dyskinesia on one side, especially when an implant is not desired.
• Lesioning (pallidotomy, thalamotomy)
  A precise lesion in the globus pallidus or thalamus, made by radiofrequency or, for those who cannot undergo open surgery, by stereotactic radiosurgery. The historical foundation of Parkinson's surgery, still useful in selected cases.

Symptom control, not a cure

Surgery controls symptoms; it does not stop the disease from progressing. Most people continue medication afterward, often at a reduced dose. With stimulation, the device is programmed over the weeks and months after surgery to find the best settings. The realistic goal is more reliable, smoother function and fewer hours lost to fluctuations and dyskinesia.

See also