A quantitative review of Botox treatment outcomes for adductor spasmodic dysphonia
By M.P Cannito, M.L. Taylor, B. Bender, and F. Boutsen
Studies of Botox treatment for adductor spasmodic dysphonia (ADSD) are numerous and varied in the methods. While generally supporting the treatment efficacy, findings are often conflicting or equivocal. This study conducted a quantitative or meta-analytic review of 30 studies providing empirical data before and after an initial Botox injection, for a total of over 900 speakers with ADSD. Effect sizes (d) and variance estimates (r2) were calculated for 249 measurements and t-tests were computed for data broken out by time post injection, injection laterality, measurement type, and sampling context. Results indicate a significant overall effect of treatment with improvement of 1.12 standard deviation units. Significant treatment effects were observed for all subcategory comparisons. Multivariate analysis of variance indicated that there were significant main effects of measurement type and sampling contexts. Physiological measures and patient self-ratings, which did not differ from each other, had significantly greater effect sizes than acoustical measurements and listeners’ perceptual judgments, which did not differ from each other. Connect speech contexts exhibited significantly greater effect sizes than sustained vowel and unspecified (e.g., self-rating) contexts. Overall, 20 per cent of the variance in the data space was explained by the effect of Botox treatment.