STN-SNr co-stimulation in Parkinson's disease: a systematic review and meta-analysis of motor and freezing-of-gait outcomes.

In 30 seconds

This systematic review and meta-analysis assessed whether adding substantia nigra pars reticulata stimulation to subthalamic nucleus deep brain stimulation improves motor function or freezing of gait in people with Parkinson’s disease. Ten studies—nine randomized trials and one observational study—included 109 unique evaluable participants. Compared with STN-only stimulation, co-stimulation showed no between-group difference in UPDRS-III scores across seven studies (73 participants; MD - 0.10, 95% CI - 1.01 to 0.81; I² = 0%; low certainty). Pooled results also did not demonstrate a consistent additional benefit for freezing of gait.

Key findings

• UPDRS-III showed no between-group difference across seven studies (73 participants; MD - 0.10, 95% CI - 1.01 to 0.81; I² = 0%; low certainty).
• Freezing of gait showed no additional benefit across six studies (86 participants; Hedges' g - 0.23, 95% CI - 1.04 to 0.59; I²_total = 85.6%; very low certainty).
• Secondary comparisons with baseline or stimulation-off favored co-stimulation for UPDRS-III (MD - 13.55) and freezing of gait (Hedges' g - 0.60), but could not isolate an incremental SNr effect.

Why it matters

Axial symptoms and freezing of gait may persist despite medication and STN stimulation, making additional stimulation targets clinically relevant to evaluate. This synthesis does not establish that adding SNr stimulation improves outcomes beyond STN-only stimulation. The low or very low certainty and substantial variability in FoG findings underscore the need to interpret apparent improvements against baseline cautiously.

What to keep in mind

The evidence included only 109 unique evaluable participants, and certainty was low for motor outcomes and very low for FoG. FoG results were heterogeneous (I²_total = 85.6%).