DBS for Parkinson’s disease can directly improve movement including slowness, stiffness, tremor, walking difficulties and involuntary movement (dyskinesias). For most patients with Parkinson’s disease, tremor is not the major reason for having DBS. DBS can allow a substantial reduction of Parkinson’s medication. DBS does not directly improve non-movement issues such as intellect, sleep disturbance or bladder function although these aspects can sometimes improve through enhanced movement and less medication. DBS for Parkinson’s disease almost always remains beneficial over the long term (for the rest of a patient’s life) but DBS does not cure Parkinson’s disease or slow progression of the disease. The aim of DBS is to improve function and quality of life. The main reasons to have DBS in Parkinson’s disease are for motor fluctuations and tremor.

Motor fluctuations:

Motor fluctuations are the variations in movement that occur over the course of a day when medication kicks in and wears off. Patients can experience ‘off’ periods (slowness and stiffness) and/or dyskinesias (involuntary movement). DBS can smooth the peaks and troughs – aiming to continuously achieve the best ‘on’ state that a patient is capable of experiencing, and with far less medication. Typically, movement problems that respond to medication (even if briefly), also respond to DBS (continuously). Movement issues that do not respond to medication do not usually respond to DBS (with the exception of tremor).

A rule of thumb is to consider DBS once motor fluctuations affect quality of life. For some patients, this can even be within a few years of being diagnosed with Parkinson’s disease. The brain target that we implant for motor fluctuations is usually the subthalamic nucleus (STN) but in older patients we may elect to implant the globus pallidus interna (GPi).

Side effects can affect almost any aspect of brain function including speech, mood, intellect and movement. Almost all side effects (if they occur) have potential to be reversed by adjusting stimulation and medication.

Overall, taking the benefits and side effects into account, studies show that DBS for motor fluctuations is capable of substantially improving function and quality of life.

Tremor:

When tremor is the sole major symptom of Parkinson’s disease, we can target the thalamus/posterior subthalamic area (PSA) (the same area we target for essential tremor). However, when tremor co-exists with significant slowness and stiffness (or for patients who are young enough that those issues are likely to emerge in future), we usually implant the subthalamic nucleus (STN) (see above).