Optimising speech outcomes in Deep Brain Stimulation for essential tremor

Abstract

Deep Brain Stimulation (DBS) is rapidly emerging as a safe and effective treatment option for mitigating the effects of tremor. Despite the relative success of DBS for treating tremor, a common and typically unquantified adverse effect of treatment is dysarthria (slurred speech). Current assessment protocols are driven by the qualitative judgements of treating clinicians and lack the sensitivity and objectivity required to make reliable decisions about treatment optimisation. Therefore we aimed to pilot a speech evaluation procedure that would form the basis of an objective clinical DBS optimisation tool for use in patients with tremor. Six patients diagnosed with essential tremor receiving treatment via deep brain stimulation of the posterior sub-thalamic nucleus were recruited. Electrical stimulation parameters (i.e., pulse rate, pulse duration, and current amplitude) were systematically adjusted and speech samples recorded to identify the patient-specific settings required for optimal therapeutic benefit (reduced tremor) with minimal adverse effects (dysarthria). Altered speech production between stimulation parameters was quantified via acoustic analysis. Measures of timing (e.g., speech rate), intonation (e.g., pitch variation) and quality (e.g., noise-to-harmonics ratio) reflected increasing/decreasing levels of dysarthria (see associated figure). Via this protocol we aim to understand the inter-relationship between the effects of the parameters as well as to develop a real-time objective system for surgeons to optimise these parameters for each patient. A secondary outcome is to increase our understanding of how electrical parameter settings are related to movement and speech, and how the optimal parameters are related to the nature of the individual’s pathology.