Importance of Differentiating Speech Fluency Disorders from Stimulation-induced Language Network Disruptions During Pre- and Intraoperative Language Mappings

Introduction: During awake intraoperative language mapping, speech disorders such as dysarthria need to be differentiated from stimulation-induced disruptions of language function. Still, the impact of speech fluency disorders such as stuttering manifesting in spontaneous repetitions, prolongations or (in-)audible pauses, on pre- and intraoperative stimulation-based language mapping has not yet been evaluated.

Methods: Patients who stutter and stuttering events were identified by a speech and language therapist (SLT) within a glioma cohort undergoing preoperative language mapping with navigated transcranial magnetic stimulation (nTMS) between 05/2018 and 01/2021. Subsequently, we compared the differentiation ability between stuttering events and stimulation-induced language network disruptions of two nTMS operators with varying degree of experience.

Results: Out of 110 glioma patients, 4.5% presented with a stutter. Both nTMS operators had a significant moderate analysis agreement for rating stuttering events as no or as a stimulation-induced language disruption (K=0.412, p=0.001). Whilst the operator with extensive experience misclassified a smaller percentage of repetitions (50.0%) and pauses in speech flow (33.3%), he misclassified a higher percentage of prolongations (30.8%) than the less experienced operator (repetitions: 90.0%; pauses: 60.0%; prolongations: 15.4%).

Conclusion : Individual expertise levels did affect the number and type of misclassified stuttering events, but these random and unpredictable disruptions of the speech flow were frequently mistaken as stimulation-induced language disruptions by both operators. This underlines the negative impact on the specificity of language mappings and the importance of differentiating speech fluency disorders during pre- and intraoperative stimulation-based language mapping.