Postoperative Programming: GPi
The general approach to programming DBS systems is similar for DBS of
the STN and of the GPi, that is, the goal is to provide the best
possible relief of cardinal symptoms of PD. In general, programming
should be initiated in the off-medication state. This may require
that antiparkinsonian medications be withheld for at least 12 hours
(usually overnight) prior to a programming session. After programming
to achieve the best relief of symptoms is completed, the patient
should take his or her PD medications and return for reassessment,
with special attention being paid to dyskinesias. These symptoms may
vary on a diurnal basis and be better in the morning and worse in the
afternoon. Monitoring for development of dyskinesias is sometimes
best accomplished in the afternoon, particularly after the patient
has taken several doses of antiparkinsonian medications.[19] If
programming in the off-medication state provides good relief of PD
symptoms and is not associated with the development of dyskinesias in
the on-medication state, no further adjustment of stimulation is
necessary. Alternatively, if the patient returns for reassessment in
the on-medication state and dyskinesias are noted, reprogramming will
be needed.

An added element of programming flexibility is present in patients
whose primary complaint is levodopa-induced dyskinesias. Symptoms in
these individuals can sometimes be managed easily by performing all
programming in the on-medication state when dyskinesias are present,
with DBS programming efforts being directed specifically at reducing
the dyskinesias. Care must be taken to en sure that beneficial
medication effects are not antagonized and that off-medication
symptoms are not exacerbated when using this approach.

As noted earlier, different regions in which stimulation has opposite
effects on dyskinesias appear to exist within the GPi. Dyskinesias
may be induced by stimulation of the dorsal GPi[1,16] and relieved by
stimulation of the ventral pallidum, although some variability in
this response exists among patients. In general, the best relief of
dyskinesias is achieved using deeper contacts, but this may
antagonize some of the beneficial effects of levodopa (especially in
treating bradykinesia). Fortunately, the antidyskinetic effects of
DBS of the GPi occur at lower amplitudes than those required to
inhibit levodopa effects, so relief of dyskinesias can usually be
accomplished without antagonizing the beneficial effects of
medications for other PD symptoms. Use of deep contacts for treatment
of dyskinesias may be appropriate for individuals in whom this is the
primary symptom, and may widen the therapeutic window for levodopa so
that any inhibition of medication effects by DBS can be balanced by
an increase in medication. If ventral pallidal stimulation provides
adequate relief of dyskinesias but results in loss of beneficial
medication effects, a compromise can generally be found by using
contacts near the central portion of the GPi, which usually provides
good relief of dyskinesias as well as tremor, rigidity, and
bradykinesia.[1,16,19] Alternatively, bilateral pallidal DBS systems
can be programmed asymmetrically by using a more proximal contact on
one side and a more distal contact on the other.[1]