Efficacy of Deep Brain Stimulation for the Treatment of Monogenic Dystonia Symptoms: A Systematic Review

BACKGROUND: Deep brain stimulation (DBS) is an essential treatment option for disabling segmental or generalized dystonia. An underlying monogenic etiology is increasingly recognized as an important predictor of DBS outcomes. Moreover, the genetic background of dystonia is continuously expanding, posing new challenges in the tailored counseling of patients regarding advanced therapies. METHODS: To improve the quality of available evidence on the efficacy of DBS for treating monogenic dystonia, we conducted a systematic review in accordance with PRISMA guidelines. We applied a rigorous methodology and maximized the amount of information provided by including all patients, regardless of age or applied rating scale. RESULTS: Our findings confirm the high probability of a good DBS outcome in patients harboring TOR1A, SGCE, PANK2, and TAF1 variants. An intermediate response was associated with KMT2B and THAP1 variants. A particularly favorable outcome with > 80% improvement in dystonia symptoms was associated with a subset of DYT-TOR1A patients and few cases with SGCE-, KMT2B-, THAP1-, GNAO1-, and TAF1-related disease. Poor study quality, non-systematic assessment of DBS response, and pooling of patients with different genetic etiologies were among the encountered limitations. CONCLUSIONS: Based on the collected evidence, we formulated recommendations for applying DBS in monogenic dystonia. Our findings, together with the cumulative literature, advocate the introduction of genetic testing in the pre-DBS work-up. They furthermore highlight the need to implement and report on systematic assessments of DBS outcomes, including mandatory patient-reported outcomes. These steps will ensure optimal counseling and continuous improvement in the care of patients with monogenic dystonia.