Assessing the effects of botulinum toxin therapy for spasmodic dysphonia: An Austria-Germany registry

Injection of Botulinum neurotoxin (BoNT) is regarded as standard treatment for spasmodic dysphonia (SD), reducing the overactivity of the affected muscles. Due to the lack of standardized outcome parameters for diagnosing SD or assessing its treatment over time, the evaluation of systematic clinical evidence on the effects of BoNT therapy on SD symptom control is difficult. The registry presented in this article aimed to evaluate outcomes after BoNT treatment in SD patients in Austria and Germany, based on selected subjective and objective voice parameters.

41 patients with SD were included in this multicentric registry, after drop-out of 2 patients the results of 39/41 (95.1%) patients could be analyzed per protocol. Demographic and treatment characteristics as well as the occurrence of therapy-related side effects were recorded. Perceptual voice sound evaluation (RBH scale), voice range profile measurements (VRP), number of spasms, and severity of voice strain were assessed. Patients were asked to complete the Voice Handicap Index (VHI-9i), the Communicative Participation Item Bank (CPIB), and indicate their perceived phonation effort on a VAS scale. The parameters were compared between baseline and 1-month post-BoNT treatment.

The patients received all BoNT type A (Xeomin^®/Merz, Allergan^®/Allergan or Dysport^®/Ipsen). SD symptoms did not affect the frequency or dynamic range of the singing voice nor did they affect MPT; in contrast all the other parameters assessed were aberrant at baseline. BoNT treatment improved Jitter-%, Dysphonia Severity Index (DSI), degrees of roughness and hoarseness, but failed to restore them to normal. BoNT significantly reduced the voice spasm and strain. Phonation effort improved by approximately 50%. VHI-9i classification was reduced from moderate to mild after treatment, and CPIB from moderate to mild. The VHI-9i results were significantly positively correlated with the CPIB results.

The results of this registry showed that BoNT injection, the current off-label treatment of SD symptoms, failed to restore normal voice quality. This registry's outcomes also indicate that the choice of the applied BoNT brand is site-specific and does not appear to be associated with differences in efficacy. We also showed that the effects of the BoNT on the SD symptoms are best described by semi-quantitative outcome measures such as spasm counts and voice strain, and by patients-reported outcome measures (PROMs), such as CPIB and VHI-9i than by more objective parameters such as frequency and dynamic range of the singing voice.