Spasmodic dysphonia
Deep brain stimulation (DBS) is a promising new therapy for patients with spasmodic dysphonia (SD). The preliminary results from a randomized controlled trial showed good clinical effects with the unilateral left thalamic stimulation in 6 right-handed patients. This suggests that the pathological process underpinning SD may have a “hemisphere dominant” pathway 1).
They described 2 patients with concurrent essential tremor and SD who had previously undergone bilateral thalamic deep brain stimulation for their limb tremor. Both patients experienced an unanticipated improvement of their SD symptoms. One patient was right-handed, and the other was mixed left-handed. To investigate the amount of SD improvement following DBS therapy in each hemisphere, 4 different settings were tested: both sides on, left side on, right side on, and both sides off. Both patients most improved following bilateral stimulation. There was, however, a powerful unilateral benefit in both patients with only a small additional benefit from bilateral stimulation. The right-handed patient improved most with left-hemisphere stimulation whereas the mixed left-handed patient improved most with right hemisphere stimulation. There was some discrepancy between the two tests applied in the second patient reflecting the known difficulties to evaluate vocal symptom improvement in SD. We discuss the possible correlation of handedness and speech hemisphere dominance as well as the need for more reliable tests to measure SD severity. Ultimately, we recommend a bilateral approach for future studies, using a patient perception test as the primary outcome and functional imaging to further investigate the correlation of handedness and the amount of hemisphere dominance in SD 2).
Poologaindran A, Ivanishvili Z, Morrison MD, Rammage LA, Sandhu MK, Polyhronopoulos NE, Honey CR. The effect of unilateral thalamic deep brain stimulation on the vocal dysfunction in a patient with spasmodic dysphonia: interrogating cerebellar and pallidal neural circuits. J Neurosurg. 2018 Feb;128(2):575-582. doi: 10.3171/2016.10.JNS161025. Epub 2017 Mar 17. PubMed PMID: 28304188.